SlideShare una empresa de Scribd logo
1 de 133
Revision-Molecular Biology
PART-2
Professor (Dr.) NAMRATA CHHABRA
MHPE, MD, MBBS, FAIMER FELLOW
PRINCIPAL-IN-CHARGE, PROFESSOR & HEAD,
DEPARTMENT OF BIOCHEMISTRY
SSR MEDICAL COLLEGE, MAURITIUS
Transcription, Translation, Genetic code and Mutations
Case studies and Multiple-choice questions
Transcription
212-Jan-21 Our Biochemistry- Namrata Chhabra
DNA Transcription
•The synthesis of an RNA molecule from DNA is called Transcription.
• All eukaryotic cells have five major classes of RNA: ribosomal RNA
(rRNA), messenger RNA (mRNA), transfer RNA (tRNA), small nuclear RNA
and microRNA (snRNA and miRNA).
•The first three are involved in protein synthesis, while the small RNAs are
involved in mRNA splicing and regulation of gene expression.
Similarities between Replication and Transcription
The processes of DNA and RNA synthesis
are similar in that they involve-
(1) the general steps of initiation,
elongation, and termination with 5' to
3' polarity;
(2) large, multicomponent initiation
complexes; and
(3) adherence to Watson-Crick base-
pairing rules.
412-Jan-21 Our Biochemistry- Namrata Chhabra
Differences between Replication and Transcription
(1) Ribonucleotides are used in RNA synthesis rather than deoxy
ribonucleotides;
(2) U replaces T as the complementary base pair for A in RNA;
(3) A primer is not involved in RNA synthesis;
(4) Only a portion of the genome is transcribed or copied into RNA,
whereas the entire genome must be copied during DNA replication;
and
(5) There is no proofreading function during RNA transcription.
512-Jan-21 Our Biochemistry- Namrata Chhabra
Template strand
Except for T for U changes, coding strand corresponds exactly to the
sequence of the RNA primary transcript, which encodes the (protein)
product of the gene.
612-Jan-21 Our Biochemistry- Namrata Chhabra
Transcription unit and Primary transcript
712-Jan-21 Our Biochemistry- Namrata Chhabra
Bacterial DNA-Dependent RNA Polymerase
The DNA-dependent RNA polymerase (RNAP) of
the bacterium Escherichia coli exists as an
approximately 400 kDa core complex consisting
of-
•two identical α subunits,
•similar but not identical β and β ' subunits, and
•an ω subunit and a
•A sigma subunit (σ)
•Beta is thought to be the catalytic subunit.
812-Jan-21 Our Biochemistry- Namrata Chhabra
Bacterial DNA-Dependent RNA Polymerase
• RNAP, a metalloenzyme, also contains two zinc molecules.
• The core RNA polymerase associates with a specific protein factor
(the sigma σ factor) that helps the core enzyme recognize and bind to
the specific deoxynucleotide sequence of the promoter region to
form the preinitiation complex (PIC)
• Bacteria contain multiple factors, each of which acts as a regulatory
protein.
912-Jan-21 Our Biochemistry- Namrata Chhabra
Mammalian DNA-Dependent RNA Polymerases
Mammalian cells possess three distinct nuclear DNA-Dependent RNA
Polymerases
• RNA polymerase I is for the synthesis of r RNA
• RNA polymerase II is for the synthesis of m RNA and miRNA
• RNA polymerase III is for the synthesis of tRNA/5S rRNA, snRNA
1012-Jan-21 Our Biochemistry- Namrata Chhabra
Overview of
Prokaryotic
DNA
Transcription
1112-Jan-21 Our Biochemistry- Namrata Chhabra
Termination of transcription (contd.)
•Beyond the hair pin, the RNA
transcript contains a strings of
Us, the bonding of Us to the
corresponding As is weak.
•This facilitates the dissociation
of the primary transcript from
DNA.
1212-Jan-21 Our Biochemistry- Namrata Chhabra
Modifications of primary transcript of mRNA in
prokaryotes
Transcription and translation are coupled in prokaryotic cells
1312-Jan-21 Our Biochemistry- Namrata Chhabra
Post Transcriptional modifications of
Ribosomal RNA (r- RNA)
• The 23S,16S, and 5S ribosomal RNAs of prokaryotes are produced form a single
RNA precursor molecule
• Cleavage and trimming are the mechanisms involved,
• Similar modifications are observed in the processing of eukaryotic r-RNA.
1412-Jan-21 Our Biochemistry- Namrata Chhabra
Post Transcriptional modifications of
Transfer RNA(t- RNA)
The extra nucleotides at both 5'
and 3' ends of t- RNA are
removed, an intron from the
anticodon arm is removed,
bases are modified and CCA
arm is attached to form the
mature functional t RNA.
1512-Jan-21 Our Biochemistry- Namrata Chhabra
Post Transcriptional modifications of
pre m- RNA
•The addition of the Guanosine
triphosphate (part of the cap is catalyzed
by the nuclear enzyme guanylyl
transferase.
•Methylation of the terminal guanine
occurs in the cytoplasm. and is catalyzed
by guanine-7-methyl transferase.
1612-Jan-21 Our Biochemistry- Namrata Chhabra
Post Transcriptional modifications of
pre m- RNA
1712-Jan-21 Our Biochemistry- Namrata Chhabra
Post Transcriptional modifications of
Pre m RNA
Introns are removed from the primary transcript in the nucleus, exons
(coding sequences) are ligated to form the mRNA molecule
1812-Jan-21 Our Biochemistry- Namrata Chhabra
Splicing of m-RNA
1912-Jan-21 Our Biochemistry- Namrata Chhabra
Clinical significance of Splicing
1) Antibodies against snRNPs
In systemic Lupus Erythematosus (SLE), an auto
immune disease, the antibodies are produced
against host proteins, including sn RNPs.
• 2) Mutations at the splice site
• Mutations at the splice site can lead to improper
splicing and the production of aberrant proteins .
• For example, some cases of Beta thalassemia are as
a result of incorrect splicing of beta globin m- RNA
due to mutation at the splice site.
2012-Jan-21 Our Biochemistry- Namrata Chhabra
Biological significance of Splicing
Tissue specific proteins are produced from the same primary transcript by
alternative splicing 2112-Jan-21 Our Biochemistry- Namrata Chhabra
Inhibitors of Transcription
• Rifampicin- binds with Beta subunit of prokaryotic
RNA polymerase,
• It is an inhibitor of prokaryotic transcription initiation.
• It binds only to bacterial RNA polymerase but not to
eukaryotic RNA polymerases.
• Therefore, Rifampicin is a powerful drug for treatment
of bacterial infections.
• Used for the treatment of tuberculosis and leprosy
2212-Jan-21 Our Biochemistry- Namrata Chhabra
Mechanism of action of Actinomycin D
• Actinomycin D- Intercalates with DNA strands
• Actinomycins inhibit both DNA synthesis and RNA
synthesis by blocking chain elongation.
• They interact with G·C base pairs as they require
the 2-amino group of guanine for binding.
• Actinomycins are used as anticancer drugs
2312-Jan-21 Our Biochemistry- Namrata Chhabra
Mitomycin and Alpha amanitin
• Mitomycin- Intercalates with DNA strands
• blocks transcription,
• used as anticancer drug
• Alpha amanitin is a molecule made from the “death
cap” mushroom and is a known potent inhibitor RNA
polymerase.
• One single mushroom could very easily lead to a fast
death in 10 days.
• The mechanism of action is that alpha amanitin inhibits
RNA polymerase –II at both the initiation and
elongation states of transcription.
2412-Jan-21 Our Biochemistry- Namrata Chhabra
Question-1
A promoter site on DNA :
a) Transcribes repressor
b) Initiates transcription
c) Codes for RNA Polymerase
d) Regulates termination
e) Translates specific proteins
2512-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
b) Initiates transcription
2612-Jan-21 Our Biochemistry- Namrata Chhabra
Question 2
The removal of introns and subsequent self-splicing of adjacent exons
occurs in some portions of primary ribosomal RNA transcripts. The
splicing of messenger RNA precursor is :
a) RNA catalyzed in the absence of proteins
b) Self-splicing
c) Carried out by spliceosomes
d) Controlled by RNA polymerase
e) Regulated by RNA helicase
2712-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
c) Carried out by spliceosomes
2812-Jan-21 Our Biochemistry- Namrata Chhabra
Question 3
In bacterial RNA synthesis, the function of factor Rho is to :
a) Increase the rate of RNA synthesis
b) Allow accurate initiation of transcription
c) Participate in termination of transcription
d) Allow the binding of RNA polymerase to the promoter
2912-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
c) Participate in termination of transcription
3012-Jan-21 Our Biochemistry- Namrata Chhabra
Question 4
Two couples present to the emergency room with severe nausea,
vomiting, and diarrhea. One of the patients admits that she served a
salad at a dinner party to which she had added a few mushrooms. With
this information, it is likely that their symptoms are as a result of
inhibition of:
a) RNA Polymerase II
b) RNA Polymerase I
c) RNA splicing
d) RNA Polyadenylation
e) RNA Polymerase III
3112-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
a) RNA Polymerase II
3212-Jan-21 Our Biochemistry- Namrata Chhabra
Question 5
A second-year student isolates nucleic acids from the cell, and finds
that some of the nucleic acids are pseudouridine and ribothymidine.
Which type of nucleic acid might have been isolated?
a) t RNA
b) rRNA
c) m RNA
d) Sn RNA
e) Mi RNA
3312-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
a) t RNA
3412-Jan-21 Our Biochemistry- Namrata Chhabra
Question 6
A 35-year-old female develops fever, night sweats, weight loss, and a
blood-tinged cough. An infectious disease doctor prescribed
Rifampicin. Which of the following enzymes is inhibited by Rifampicin?
a) DNA-dependent DNA polymerase
b) DNA-dependent RNA polymerase
c) RNA-dependent DNA polymerase
d) RNA-dependent RNA polymerase
e) Reverse transcriptase
3512-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
b) DNA-dependent RNA polymerase
3612-Jan-21 Our Biochemistry- Namrata Chhabra
Question 6
Actinomycin D, is an inhibitor of transcription, which acts as by
inhibiting-
a) β- subunit of prokaryotic RNA polymerase
b) Movement of RNA polymerase along the DNA template
c) Sigma subunit of RNA polymerase
d) Prokaryotic Topoisomerase II
e) Prokaryotic helicase
3712-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
b) Movement of RNA polymerase along the DNA template
3812-Jan-21 Our Biochemistry- Namrata Chhabra
Question 7
The initial RNA produced during the translation of DNA to RNA, which
contains both the coding exons and the non-coding introns, is known as
which of the following?
a) Amino acyl transfer RNA
b) m RNA
c) Ribosomal RNA
d) Heterogeneous nuclear RNA
e) Small nuclear RNA
3912-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
d) Heterogeneous nuclear RNA
4012-Jan-21 Our Biochemistry- Namrata Chhabra
Question 8
Which of the following processes is not involved in the post
transcriptional processing of t-RNA?
A) Attachment of poly A tail
B) Trimming
C) Splicing
D) Attachment of CCA arm
E) Base modification
4112-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
A) Attachment of poly A tail
4212-Jan-21 Our Biochemistry- Namrata Chhabra
Genetic code
4312-Jan-21 Our Biochemistry- Namrata Chhabra
Genetic Code
 Genetic code is a dictionary that corresponds with sequence of
nucleotides and sequence of Amino Acids.
 Words in dictionary are in the form of codons
 Each codon is a triplet of nucleotides
 64 codons in total and three out of these are Non Sense
codons.
 61 codons for 20 amino acids
4412-Jan-21 Our Biochemistry- Namrata Chhabra
4512-Jan-21 Our Biochemistry- Namrata Chhabra
Genetic Code-Characteristics
 Specificity- Genetic code is specific (Unambiguous)
 A specific codon always codes for the same amino acid.
e.g., UUU codes for Phenyl Alanine, it can not code for any other
amino acid.
4612-Jan-21 Our Biochemistry- Namrata Chhabra
Genetic Code-Universal
Universal- In all living organism Genetic code is the same.
 The exception to universality is found in mitochondrial codons
where AUA codes for methionine and UGA for tryptophan,
instead of isoleucine and termination codon respectively of
cytoplasmic protein synthesizing machinery.
 AGA and AGG code for Arginine in cytoplasm but in
mitochondria they are termination codons.
4712-Jan-21 Our Biochemistry- Namrata Chhabra
Genetic Code-Redundant
Redundant- Genetic code is
Redundant, also called
Degenerate.
Although each codon
corresponds to a single amino
acid, but a single amino acid
can have multiple codons.
Except Tryptophan and
Methionine each amino acid
has multiple codons.
4812-Jan-21 Our Biochemistry- Namrata Chhabra
Genetic Code- Non-Overlapping and Non-
Punctuated
 All codons are independent sets of 3 bases.
 There is no overlapping ,
 Codon is read from a fixed starting point as a continuous
sequence of bases, taken three at a time.
 The starting point is extremely important, and this is called
Reading frame.
4912-Jan-21 Our Biochemistry- Namrata Chhabra
Non-Sense Codons
 There are 3 codons out of 64 in
genetic code which do not encode
for any Amino Acid.
 These are called termination
codons or stop codons or
nonsense codons. The stop
codons are UAA, UAG, and
UGA. They encode no amino
acid. The ribosome pauses and
falls off the mRNA.
5012-Jan-21 Our Biochemistry- Namrata Chhabra
Initiator codon
 AUG is the initiator codon in majority of proteins-
 In a few cases GUG may be the initiator codon
 Methionine is the only amino acid specified by just one codon,
AUG.
5112-Jan-21 Our Biochemistry- Namrata Chhabra
Wobbling phenomenon
 The rules of base pairing are relaxed
at the third position, so that a base can
pair with more than one
complementary base.
 Some tRNA anticodons
have Inosine at the third position.
 Inosine can pair with U, C, or A. This
means that we don't need 61 different
tRNA molecules, only half as many
are required.
52
t RNA (first
base)
m RNA
(Third base)
Base pairing
C G Traditional
A U Traditional
U A Traditional
U G Nontraditio
nal
G C Traditional
G U Nontraditio
nal
I U Nontraditio
nal
I C Nontraditio
nal
I A Nontraditio
nal
12-Jan-21 Our Biochemistry- Namrata Chhabra
Question 9
The following are all characteristics of genetic code except:
a. Universal
b. Degenerate
c. Non-overlapping
d. Ambiguous
5312-Jan-21 Our Biochemistry- Namrata Chhabra
ANSWER
d. Ambiguous
5412-Jan-21 Our Biochemistry- Namrata Chhabra
Question 10
Which of the following is the initiator codon ?
a) AGG
b) AUG
c) AUC
d) AUA
e) AUU
5512-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
b) AUG
5612-Jan-21 Our Biochemistry- Namrata Chhabra
Question 10
Which statement about genetic code is most accurate?
a) Information is stored as sets of dinucleotide repeats called codons
b) The code is degenerate (more than one codon may exist for a single
amino acid)
c) Information is stored as sets of trinucleotide repeats called codons.
d) There are 64 codons, all of which code for amino acids.
e) The sequence of the codons that make up a gene exhibits an exact
linear correspondence to the sequence of amino acids in the
translated protein.
5712-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
e) The sequence of the codons that make up a gene exhibits an exact
linear correspondence to the sequence of amino acids in the translated
protein.
5812-Jan-21 Our Biochemistry- Namrata Chhabra
59
TRANSLATION
12-Jan-21 Our Biochemistry- Namrata Chhabra
Translation
• The pathway of protein synthesis is called Translation
because the ‘language’ of the nucleotide sequence on the
mRNA is translated into the language of the amino acid
sequence.
• The mRNA is translated from its 5’end to its 3’end , producing
a protein synthesized from its amino terminal end to its
carboxyl terminal end.
6012-Jan-21 Our Biochemistry- Namrata Chhabra
Components required for Translation
• Amino acids
• Transfer RNA
• Messenger RNA
• Aminoacyl t RNA synthetase
• Functionally competent ribosomes
• Protein factors
• ATP and GTP as a source of energy
6112-Jan-21 Our Biochemistry- Namrata Chhabra
Steps of Protein Synthesis
The process of protein
synthesis is divided into 3
stages-
- Initiation
- Elongation
- Termination
6212-Jan-21 Our Biochemistry- Namrata Chhabra
Initiation-
The small ribosomal subunit binds to Initiation Factor 3 (IF3).
The small subunit/IF3 complex binds to the mRNA.
Specifically, it binds to the sequence AGGAGG, known as the
Shine-Delgarno sequence, which is found in all prokaryotic
mRNAs.
6412-Jan-21 Our Biochemistry- Namrata Chhabra
Meanwhile, the fmet tRNA binds to Initiation Factor 2 (IF2), which
promotes binding of the tRNA to the start codon.
6512-Jan-21 Our Biochemistry- Namrata Chhabra
The small subunit/IF3 complex scans along the mRNA until it
encounters the start codon. The tRNA/IF2 complex also binds
to the start codon. This complex of the small ribosomal
subunit, IF3, initiator tRNA, and IF2 is called the initiation
complex.
6612-Jan-21 Our Biochemistry- Namrata Chhabra
At this point, the large ribosomal subunit joins in. A molecule of
GTP is hydrolyzed, and the initiation factors are released. The
ribosomal complex is now ready for protein synthesis.
6712-Jan-21 Our Biochemistry- Namrata Chhabra
When the ribosome is assembled, two tRNA binding sites are created;
these are designated 'P' and 'A' (P stands for peptidyl, A stands for
amino acyl). The initiator tRNA is in the P site, and the A site will be
filled by the tRNA with the anticodon that is complementary to the
codon next to the start. (In this case, it is the tRNA that binds proline.)
6812-Jan-21 Our Biochemistry- Namrata Chhabra
When the second tRNA base pairs with the appropriate codon in the mRNA,
an enzyme called peptidyl transferase catalyzes the formation of a peptide
bond between the two amino acids present (while breaking the bond
between fmet and its tRNA).This activity is intrinsic to the 23S r RNA found in
the large subunit. Since the r RNA catalyzes this process , it is referred to as
the Ribozyme
6912-Jan-21 Our Biochemistry- Namrata Chhabra
Elongation
At this point, the whole ribosome shifts over one codon. This shift
requires several elongation factors (not shown) and energy from the
hydrolysis of GTP. The result of the shift is that the uncharged tRNA that
was in the P site is ejected, and the tRNA that was in the A site is now in
the P site. The A site is free to accept the tRNA molecule with the
appropriate anticodon for the next codon in the mRNA.
7012-Jan-21 Our Biochemistry- Namrata Chhabra
The next tRNA base pairs with the next codon, and peptidyl transferase
catalyzes the formation of a peptide bond between the new amino acid
and the growing peptide chain.
7112-Jan-21 Our Biochemistry- Namrata Chhabra
Termination
When a termination codon enters the A site, translation halts. This is because there
is no tRNA with an anti codon that is complementary to any of the stop codons.
7212-Jan-21 Our Biochemistry- Namrata Chhabra
Inhibitors of protein synthesis
• The tetracyclines (tetracycline, doxycycline, demeclocycline,
minocycline, etc.) block bacterial translation by binding reversibly to
the 30S subunit and distorting it in such a way that the anticodons of
the charged tRNAs cannot align properly with the codons of the
mRNA.
• Puromycin structurally binds to the amino acyl t RNA and becomes
incorporated into the growing peptide chain thus causing inhibition of
the further elongation.
7312-Jan-21 Our Biochemistry- Namrata Chhabra
Inhibitors of protein synthesis
• Chloramphenicol inhibits prokaryotic peptidyl transferase
• Clindamycin and Erythromycin bind irreversibly to a site on
the 50 s subunit of the bacterial ribosome thus inhibit
translocation.
• Diphtheria toxin inactivates the eukaryotic elongation
factors thus prevent translocation.
7412-Jan-21 Our Biochemistry- Namrata Chhabra
Post Translational Modifications
The newly synthesized protein is modified to become functionally
active. The various post translational modifications are as follows-
-Trimming
-Covalent Alterations
a)Phosphorylation
b) Glycosylation
c) Hydroxylation
d) Gamma carboxylation
e) Isoprenylation
-Protein degradation 7512-Jan-21 Our Biochemistry- Namrata Chhabra
Post Translational Modifications
Trimming removes excess amino acids.
Phosphorylation may activate or inactivate the protein
Glycosylation targets a protein to become a part of the plasma
membrane or lysosomes or be secreted out of the cell
Hydroxylation such as seen in collagen is required for acquiring the
three-dimensional structure and for imparting strength
Defective proteins or destined for turn over are marked for destruction
by attachment of a Ubiquitin protein. Proteins marked in this way are
degraded by a cellular component known as the Proteasome.
7612-Jan-21 Our Biochemistry- Namrata Chhabra
Question 11
The initiation of translation in eukaryotes requires which of the
following:
a. Initiation factor (IF-2)
b. Elongation factor (EF)-2
c. A 40-S ribosomal subunit
d. Methionyl-tRNA (f Met).
7712-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
c) A 40-S ribosomal subunit
7812-Jan-21 Our Biochemistry- Namrata Chhabra
Question 12
Which of the following statements about prokaryotic translation is
incorrect?
a. Transcription and translation are simultaneous
b. Initiation takes place with the help of Methionyl-tRNA (f Met)
c. 20 S and 60 S subunits together form a ribosome of 80 S
d. Chloramphenicol inhibits prokaryotic translation.
7912-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
c. 20 S and 60 S subunits together form a ribosome of 80 S
8012-Jan-21 Our Biochemistry- Namrata Chhabra
Question 13
Which of the following components is required in prokaryotic protein
synthesis?
a. Aminoacyl t RNA synthetase
b. Helicase
c. Topoisomerase
d. Primase.
8112-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
a) Aminoacyl t RNA synthetase
8212-Jan-21 Our Biochemistry- Namrata Chhabra
Question 14
A 34-year-old female develops a nonproductive cough and a low-grade
fever. The attending physician suspects Mycoplasma pneumonia and
starts empirically with Erythromycin.
Which of the following describes the mechanism of action of
Erythromycin?
a) Inhibits the 50S ribosomal subunit.
b) Inhibits the initiation factor- 1(IF-1).
c) Binds to shine Dalgarno sequence.
d) Inhibits the incoming aminoacyl tRNA.
8312-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
a) Inhibits the 50S ribosomal subunit
8412-Jan-21 Our Biochemistry- Namrata Chhabra
Question 15
A -4-year-old girl has been brought to the Pediatric OPD with fever and
cough that sounds like a “whoop”. The pediatrician learns that the child
has not been properly immunized and has yet to receive Pertussis
vaccination.
The mechanism by which the pertussis toxin causes cell death is
through the inhibition of:
a. Translocase
b. Peptidyl transferase
c. Elongation factor (EF)-2
d. Aminoacyl t-RNA synthetase.
8512-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
a. Translocase
8612-Jan-21 Our Biochemistry- Namrata Chhabra
Question 16
An 18-year-old girl has been advised to start with Tetracycline for the
treatment for her acne. Which of the following statements best
describes the mechanism of action of Tetracycline?
Tetracycline:
a. binds reversibly to the 30S subunit and distorts it.
b. inhibits prokaryotic Peptidyl Transferase
c. inactivates the prokaryotic elongation factors
d. structurally binds to the aminoacyl t RNA.
8712-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
a. binds reversibly to the 30S subunit and distorts it.
8812-Jan-21 Our Biochemistry- Namrata Chhabra
Question 17
A 34-year-old has reported to the Medical OPD with a high -grade fever,
dry cough, headache, loss of appetite, and pain abdomen lasting from
the past seven days. She has been diagnosed with typhoid fever, for
which she has been started with Chloramphenicol.
The drug acts by inhibiting prokaryotic :
a. Translocase
b. Peptidyl transferase
c. Initiation factor (IF)-2
d. Aminoacyl t-RNA synthetase.
8912-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
b. Peptidyl transferase
9012-Jan-21 Our Biochemistry- Namrata Chhabra
Question 18
Immunoglobulins, hemoglobin, and collagen are modified post-
translationally by the process of:
a) Hydroxylation
b) Subunit aggregation
c) Methylation
d) Trimming.
e) Carboxylation
9112-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
b) Subunit aggregation
9212-Jan-21 Our Biochemistry- Namrata Chhabra
Mutations
9312-Jan-21 Our Biochemistry- Namrata Chhabra
INTRODUCTION
● A mutation is a permanent change in the
nucleotide sequence of a gene.
● Mutations may be either gross, so that
large areas of chromosome are changed,
● or may be subtle with a change in one or a
few nucleotides.
Mutations
Large scale
Point
mutations
94
Causes of Mutations
SPONTANEOS
INDUCED BY
MUTAGENS
95
Spontaneous Mutations
SPONTANEOUSMUTATIONS
Tautomerism
Deamination
Depurination
Transition
Transversion
96
Tautomerism
97
Deamination of bases
98
Depurination
and
deamination
99
Transition and transversion
100
Mutagens
● Chemicals
o Nitroso compounds
o Hydroxylamine NH2OH
o Base analogs
o Simple chemicals (e.g. acids)
○ Alkylating & methylating agents (e.g. N-
ethyl-N-nitrosourea (ENU)
101
Mutagens
● Chemicals
o Polycyclic aromatic hydrocarbons e.g. benzopyrenes
o DNA intercalating agents (e.g. ethidium bromide)
o DNA cross linker (e.g. platinum)
o Oxidative damage caused by oxygen(O)radicals
102
Mutagens
❖ Radiations
● Ultraviolet radiation (non-ionizing radiation) - excites electrons to a higher
energy level. DNA absorbs ultraviolet light. Two nucleotide bases in DNA -
cytosine and thymine-are most vulnerable to excitation that can change base-
pairing properties. UV light can induce adjacent thymine bases in a DNA strand
to pair with each other, as a bulky dimer.
● Ionizing radiation
103
Mutagens
❖ Biological-
○ Viruses (DNA or RNA viruses)
○ Transposons
104
Classification of point mutations
Point
mutations
Substitution
Insertion
Deletion
105
Point
mutations
106
Insertional
mutagenesis
● Insertions in the coding
region of a gene may
alter splicing of the
mRNA (splice site
mutation), or
● cause a shift in the
reading frame (frame
shift), both of which can
significantly alter the
gene product.
107
A) Point mutations
iii) Deletions remove one
nucleotide from the DNA.
Like insertions, these
mutations can alter the
reading frame of the gene.
108
B) Large-scale mutations
B) Large-scale mutations in chromosomal structure, including:
Amplifications (or gene duplications) leading to multiple copies of all
chromosomal regions, increasing the dosage of the genes located within
them.
109
Gene amplification
110
B) Large-scale mutations
c) Chromosomal Mutations:
○ Chromosomal translocations: interchange of genetic parts from
nonhomologous chromosomes.
○ Interstitial deletions: an intra-chromosomal deletion that removes a
segment of DNA from a single chromosome, thereby apposing
previously distant genes.
○ Chromosomal inversions: reversing the orientation of a
chromosomal segment.
111
Effects of point mutations
Single-base changes in the mRNA molecules may have one of several effects
when translated into protein:
1. Silent mutations-There may be no detectable effect because of the
degeneracy of the code.
2. This would be more likely if the changed base in the mRNA molecule
were to be at the third nucleotide of a codon.
112
Effects of point mutations
(2) A missense effect will occur when a different amino acid is incorporated
at the corresponding site in the protein molecule. This mistaken amino
acid—or missense, depending upon its location in the specific protein—
might be acceptable, partially acceptable, or unacceptable to the function
of that protein molecule.
Most single-base changes would result in the replacement of one amino acid
by another with rather similar functional groups. This is an effective
mechanism to avoid drastic change in the physical properties of a protein
molecule.
113
a) Acceptable Missense mutations
● The sequencing of a large number of hemoglobin mRNAs and genes from many
individuals has shown that the codon for valine at position 67 of the chain of
hemoglobin is not identical in all persons who possess a normally functional chain of
hemoglobin.
● The codon changes by point mutation from GUU (of valine) to GAU of Aspartic acid
in Hb Bristol.
● Similarly in Hb Sydney the codon changes from GUU to GCU for Alanine.
● Both Hb Bristol and Hb Sydney are normal Hb variants with normal oxygen carrying
capacity.
● Thus these are acceptable mutations.
114
Partially acceptable Missense mutations
● Clearly, this missense mutation hinders normal function and
results in sickle cell anemia when the mutant gene is present in
the homozygous state.
● The glutamate-to-valine change may be considered to be
partially acceptable because hemoglobin S does bind and
release oxygen, although abnormally.
115
c) Unacceptable Missense Mutations
● The hemoglobin M mutations generate molecules that allow the Fe2+ of the heme
moiety to be oxidized to Fe3+, producing methemoglobin.
● Here the single nucleotide change alters the properties of a protein to such an extent
that it becomes non- functional.
● Hb M results from histidine to tyrosine substitution.
● Distal Histidine of alpha chain of Globin is replaced by Tyrosine.
● The codon CAU is changed to UAU with the resultant incorporation of Tyrosine and
formation of MetHb.
● Met hemoglobin cannot transport oxygen.
116
(3) A nonsense mutation
A nonsense codon may appear that would then result in the premature
termination of a peptide chain and the production of only a fragment of the
intended protein molecule.
The probability is high that a prematurely terminated protein molecule or
peptide fragment will not function in its assigned role.
117
(3) A nonsense mutation
● The codon UAC for Tyrosine may be mutated to UAA or UAG, both are stop
codons. Beta Thalassemia is an example of nonsense mutation.
● In certain conditions as a result of mutational event the stop codon may be
changed to normal codon (UAA to CAA) .
● This results in the elongation of protein to produce “Run on polypeptides”.
The resultant protein is a functionally abnormal protein.
118
Frameshift Mutations
● A frame shift mutation is a mutation caused by inserts or deletes of a number of
nucleotides from a DNA sequence.
● Due to the triplet nature of gene expression by codons, the insertion or deletion
can disrupt the reading frame, or the grouping of the codons, resulting in a
completely different translation from the original.
● The earlier in the sequence the deletion or insertion occurs, the more altered
the protein produced is.
119
Triplet deletion
A triplet deletion removes exactly
one amino acid from the
polypeptide ,the most common
mutation in cystic fibrosis is Delta
F508 (i.e. deletion of amino acid
number 508 (a phenylalanine, F).
120
Trinucleotide expansion
● The commonest inherited cause of mental retardation is a
syndrome originally known as Martin-Bell syndrome.
● Patients are most usually male, have a characteristic
elongated face and numerous other abnormalities
including greatly enlarged testes.
● In 1969 the name of the syndrome was changed to the
fragile X syndrome.
121
Trinucleotide expansion
● The mutation was tracked down to a trinucleotide expansion in
the gene now named FMR1 (Fragile site with Mental
Retardation).
● A number of diseases have now been ascribed to trinucleotide
expansions.
● These include Huntington's disease and Myotonic dystrophy.
122
Gene deletions
● Alpha Thalassemia is an
example of Gene
deletion.
● The clinical
manifestations are as per
the number of genes
deleted.
123
Consequences of Mutations
Harmful mutations
● Changes in DNA caused by mutation can cause errors in protein
sequence, creating partially or completely non-functional proteins.
● To function correctly, each cell depends on thousands of proteins to
function in the right places at the right times.
● When a mutation alters a protein that plays a critical role in the body, a
medical condition can result.
● A condition caused by mutations in one or more genes is called a genetic
disorder.
124
Consequences of Mutations
● If a mutation is present in a germ cell, it can give rise to
offspring that carries the mutation in all of its cells.
● This is the case in hereditary diseases.
● On the other hand, a mutation can occur in a somatic cell of an
organism.
● Such mutations will be present in all descendants of this cell,
and certain mutations can cause the cell to become malignant,
and thus cause cancer.
125
Consequences of Mutations
Beneficial mutations
● A very small percentage of all mutations actually have a positive effect.
● These mutations lead to new versions of proteins that help an organism
and its future generations better adapt to changes in their environment.
● For example, a specific 32 base pair deletion in human CCR5 (CCR5-Δ32)
confers HIV resistance to homozygotes and delays AIDS onset in
heterozygotes.
● The CCR5 mutation is more common in those of European descent.
126
Question 19
Triple repeat sequence disease occurs in:
a) Alzheimer’s disease
b) Cystic fibrosis
c) Ataxia telangiectasia
d) Huntington’s chorea
12712-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
d) Huntington’s chorea
12812-Jan-21 Our Biochemistry- Namrata Chhabra
Question 20
Which of the following changes in mRNA (resulting form point
mutation) would result in the synthesis of a protein identical to the
normal protein?
a. UCA – UAA
b. UCA- CCA
c. UCA- UCU
d. UCA- ACA
12912-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
c. UCA- UCU
13012-Jan-21 Our Biochemistry- Namrata Chhabra
Question 21
A-58-year-old male has recently been diagnosed with
hemochromatosis. He presents with bronze discoloration of the skin
and is found to have elevated plasma glucose and ferritin levels. The
physician finds that he is carrying a mutation where tyrosine is
substituted for Cysteine of the HFE gene. This disease results from
which of the following mutations?
a. Silent
b. Nonsense
c. Missense
d. Frameshift.
13112-Jan-21 Our Biochemistry- Namrata Chhabra
Answer
c. Missense
13212-Jan-21 Our Biochemistry- Namrata Chhabra
Thank you
13312-Jan-21 Our Biochemistry- Namrata Chhabra

Más contenido relacionado

La actualidad más candente

Divakaran Molecular level of Eukaryotic translation
Divakaran Molecular level of Eukaryotic translationDivakaran Molecular level of Eukaryotic translation
Divakaran Molecular level of Eukaryotic translationaishudiva
 
5’ capping
5’ capping5’ capping
5’ cappingEmaSushan
 
Structure and function of Messenger RNA (mRNA )
Structure and function of Messenger RNA (mRNA )Structure and function of Messenger RNA (mRNA )
Structure and function of Messenger RNA (mRNA )ICHHA PURAK
 
Eukaryotes replication
Eukaryotes replicationEukaryotes replication
Eukaryotes replicationkrekar mardan
 
Phage stratagies
Phage stratagiesPhage stratagies
Phage stratagiesAmith Reddy
 
Telomerase replication
Telomerase replicationTelomerase replication
Telomerase replicationArchana Shaw
 
Expression of Immunoglobin gene
Expression of Immunoglobin geneExpression of Immunoglobin gene
Expression of Immunoglobin geneHadia Azhar
 
Regulation of gene expression saranya
Regulation of gene expression saranyaRegulation of gene expression saranya
Regulation of gene expression saranyaSaranya Sankar
 
Prokaryotic DNA replication
Prokaryotic DNA replicationProkaryotic DNA replication
Prokaryotic DNA replicationMoumita Paul
 
RNA-Protein interactions-brief.pptx
RNA-Protein interactions-brief.pptxRNA-Protein interactions-brief.pptx
RNA-Protein interactions-brief.pptxZEPHYRCKOTTAYIL
 
Gene Expression in Eukaryotes
Gene Expression in EukaryotesGene Expression in Eukaryotes
Gene Expression in EukaryotesDr.M.Prasad Naidu
 
Endoplasmic reticulum[1]
Endoplasmic reticulum[1]Endoplasmic reticulum[1]
Endoplasmic reticulum[1]Dilip Pandya
 
Regulation of gene expression in eukaryotes
Regulation of gene expression in eukaryotesRegulation of gene expression in eukaryotes
Regulation of gene expression in eukaryotesNamrata Chhabra
 
Transcription
Transcription Transcription
Transcription ranjani n
 
Molecular Biology Revision-Part1
Molecular Biology Revision-Part1Molecular Biology Revision-Part1
Molecular Biology Revision-Part1Namrata Chhabra
 

La actualidad más candente (20)

Divakaran Molecular level of Eukaryotic translation
Divakaran Molecular level of Eukaryotic translationDivakaran Molecular level of Eukaryotic translation
Divakaran Molecular level of Eukaryotic translation
 
5’ capping
5’ capping5’ capping
5’ capping
 
Structure and function of Messenger RNA (mRNA )
Structure and function of Messenger RNA (mRNA )Structure and function of Messenger RNA (mRNA )
Structure and function of Messenger RNA (mRNA )
 
Eukaryotes replication
Eukaryotes replicationEukaryotes replication
Eukaryotes replication
 
Phage stratagies
Phage stratagiesPhage stratagies
Phage stratagies
 
Telomerase replication
Telomerase replicationTelomerase replication
Telomerase replication
 
Expression of Immunoglobin gene
Expression of Immunoglobin geneExpression of Immunoglobin gene
Expression of Immunoglobin gene
 
Regulation of gene expression saranya
Regulation of gene expression saranyaRegulation of gene expression saranya
Regulation of gene expression saranya
 
Sos repair
Sos repairSos repair
Sos repair
 
Prokaryotic DNA replication
Prokaryotic DNA replicationProkaryotic DNA replication
Prokaryotic DNA replication
 
Transcription
TranscriptionTranscription
Transcription
 
RNA-Protein interactions-brief.pptx
RNA-Protein interactions-brief.pptxRNA-Protein interactions-brief.pptx
RNA-Protein interactions-brief.pptx
 
Gene Expression in Eukaryotes
Gene Expression in EukaryotesGene Expression in Eukaryotes
Gene Expression in Eukaryotes
 
Gene expression regulation emphasizing hormone action
Gene expression regulation emphasizing hormone actionGene expression regulation emphasizing hormone action
Gene expression regulation emphasizing hormone action
 
Endoplasmic reticulum[1]
Endoplasmic reticulum[1]Endoplasmic reticulum[1]
Endoplasmic reticulum[1]
 
Regulation of gene expression in eukaryotes
Regulation of gene expression in eukaryotesRegulation of gene expression in eukaryotes
Regulation of gene expression in eukaryotes
 
Transcription
Transcription Transcription
Transcription
 
Molecular Biology Revision-Part1
Molecular Biology Revision-Part1Molecular Biology Revision-Part1
Molecular Biology Revision-Part1
 
Cell Cycle Regulation
Cell Cycle RegulationCell Cycle Regulation
Cell Cycle Regulation
 
Transcription in eukaryotes
Transcription in eukaryotesTranscription in eukaryotes
Transcription in eukaryotes
 

Similar a Revision Molecular biology- Part 2

Gene expresion transcription.pdf
 Gene expresion transcription.pdf Gene expresion transcription.pdf
Gene expresion transcription.pdfMohamed Alashram
 
DNA Transcription and RNA Processing
DNA Transcription and RNA Processing DNA Transcription and RNA Processing
DNA Transcription and RNA Processing Ashok Katta
 
Lecture 2. Chemistry of NA Purines & Pyrimidines.ppt
Lecture 2. Chemistry of NA Purines & Pyrimidines.pptLecture 2. Chemistry of NA Purines & Pyrimidines.ppt
Lecture 2. Chemistry of NA Purines & Pyrimidines.pptDr Vishnu Kumar
 
DNA Transcription- Part-1
DNA Transcription- Part-1DNA Transcription- Part-1
DNA Transcription- Part-1Namrata Chhabra
 
Transcription in Pro- & eukaryotes
Transcription in Pro- & eukaryotesTranscription in Pro- & eukaryotes
Transcription in Pro- & eukaryotesNurulhasanKhatri
 
cell biology and biochemistry
cell biology and biochemistrycell biology and biochemistry
cell biology and biochemistryNiweditaKumari2
 
CENTRAL DOGMA OF MOLECULAR.pptx
CENTRAL DOGMA OF MOLECULAR.pptxCENTRAL DOGMA OF MOLECULAR.pptx
CENTRAL DOGMA OF MOLECULAR.pptxjohndarwinbarcena1
 
Transcription of DNA to RNA by Dr. Anurag Yadav
Transcription of DNA to RNA by Dr. Anurag YadavTranscription of DNA to RNA by Dr. Anurag Yadav
Transcription of DNA to RNA by Dr. Anurag YadavDr Anurag Yadav
 
Transcription process
Transcription processTranscription process
Transcription processTouheed Ovi
 
Biosynthesis of protein in eukariotes
Biosynthesis of protein in eukariotesBiosynthesis of protein in eukariotes
Biosynthesis of protein in eukariotesKAUSHAL SAHU
 
Transcription II- Post transcriptional modifications and inhibitors of Transc...
Transcription II- Post transcriptional modifications and inhibitors of Transc...Transcription II- Post transcriptional modifications and inhibitors of Transc...
Transcription II- Post transcriptional modifications and inhibitors of Transc...Namrata Chhabra
 

Similar a Revision Molecular biology- Part 2 (20)

Gene expresion transcription.pdf
 Gene expresion transcription.pdf Gene expresion transcription.pdf
Gene expresion transcription.pdf
 
DNA Transcription and RNA Processing
DNA Transcription and RNA Processing DNA Transcription and RNA Processing
DNA Transcription and RNA Processing
 
Lecture 2. Chemistry of NA Purines & Pyrimidines.ppt
Lecture 2. Chemistry of NA Purines & Pyrimidines.pptLecture 2. Chemistry of NA Purines & Pyrimidines.ppt
Lecture 2. Chemistry of NA Purines & Pyrimidines.ppt
 
DNA Transcription- Part-1
DNA Transcription- Part-1DNA Transcription- Part-1
DNA Transcription- Part-1
 
Transcription in Pro- & eukaryotes
Transcription in Pro- & eukaryotesTranscription in Pro- & eukaryotes
Transcription in Pro- & eukaryotes
 
Post transcriptional modification ( splicing mechanisms)
Post transcriptional modification ( splicing mechanisms)Post transcriptional modification ( splicing mechanisms)
Post transcriptional modification ( splicing mechanisms)
 
Gene expression
Gene expressionGene expression
Gene expression
 
Geneexpression
GeneexpressionGeneexpression
Geneexpression
 
CELL PHYSIO 202.ppt
CELL PHYSIO 202.pptCELL PHYSIO 202.ppt
CELL PHYSIO 202.ppt
 
cell biology and biochemistry
cell biology and biochemistrycell biology and biochemistry
cell biology and biochemistry
 
Rna structure
Rna structureRna structure
Rna structure
 
CENTRAL DOGMA OF MOLECULAR.pptx
CENTRAL DOGMA OF MOLECULAR.pptxCENTRAL DOGMA OF MOLECULAR.pptx
CENTRAL DOGMA OF MOLECULAR.pptx
 
Transcription of DNA to RNA by Dr. Anurag Yadav
Transcription of DNA to RNA by Dr. Anurag YadavTranscription of DNA to RNA by Dr. Anurag Yadav
Transcription of DNA to RNA by Dr. Anurag Yadav
 
Transcription process
Transcription processTranscription process
Transcription process
 
Biosynthesis of protein in eukariotes
Biosynthesis of protein in eukariotesBiosynthesis of protein in eukariotes
Biosynthesis of protein in eukariotes
 
Lecture 8
Lecture 8Lecture 8
Lecture 8
 
Cell physio 202
Cell physio 202Cell physio 202
Cell physio 202
 
physiology...protein
physiology...proteinphysiology...protein
physiology...protein
 
5.RNA Processing.pptx
5.RNA Processing.pptx5.RNA Processing.pptx
5.RNA Processing.pptx
 
Transcription II- Post transcriptional modifications and inhibitors of Transc...
Transcription II- Post transcriptional modifications and inhibitors of Transc...Transcription II- Post transcriptional modifications and inhibitors of Transc...
Transcription II- Post transcriptional modifications and inhibitors of Transc...
 

Más de Namrata Chhabra

Applications of Recombinant DNA Technology
Applications of Recombinant DNA Technology Applications of Recombinant DNA Technology
Applications of Recombinant DNA Technology Namrata Chhabra
 
Recombinant DNA Technology- Part 1.pdf
Recombinant DNA Technology- Part 1.pdfRecombinant DNA Technology- Part 1.pdf
Recombinant DNA Technology- Part 1.pdfNamrata Chhabra
 
Polymerase Chain Reaction- Principle, procedure, and applications of PCR
Polymerase Chain Reaction- Principle, procedure, and applications of PCRPolymerase Chain Reaction- Principle, procedure, and applications of PCR
Polymerase Chain Reaction- Principle, procedure, and applications of PCRNamrata Chhabra
 
Clinical case discussions
Clinical case discussions Clinical case discussions
Clinical case discussions Namrata Chhabra
 
Basal metabolic rate (BMR)- Factors affecting BMR, measurement and clinical s...
Basal metabolic rate (BMR)- Factors affecting BMR, measurement and clinical s...Basal metabolic rate (BMR)- Factors affecting BMR, measurement and clinical s...
Basal metabolic rate (BMR)- Factors affecting BMR, measurement and clinical s...Namrata Chhabra
 
Selenium- chemistry, functions and clinical significance
Selenium- chemistry, functions and clinical significanceSelenium- chemistry, functions and clinical significance
Selenium- chemistry, functions and clinical significanceNamrata Chhabra
 
Folic acid- Chemistry, One carbon metabolism and megaloblastic anemia
Folic acid- Chemistry, One carbon metabolism and megaloblastic anemiaFolic acid- Chemistry, One carbon metabolism and megaloblastic anemia
Folic acid- Chemistry, One carbon metabolism and megaloblastic anemiaNamrata Chhabra
 
Vitamin B12-Chemistry, functions and clinical significance
Vitamin B12-Chemistry, functions and clinical significanceVitamin B12-Chemistry, functions and clinical significance
Vitamin B12-Chemistry, functions and clinical significanceNamrata Chhabra
 
Sugar derivatives and reactions of monosaccharides
Sugar derivatives and reactions of monosaccharidesSugar derivatives and reactions of monosaccharides
Sugar derivatives and reactions of monosaccharidesNamrata Chhabra
 
Chemistry of carbohydrates part 2
Chemistry of carbohydrates part 2 Chemistry of carbohydrates part 2
Chemistry of carbohydrates part 2 Namrata Chhabra
 
Chemistry of carbohydrates - General introduction and classification
Chemistry of carbohydrates - General introduction and classificationChemistry of carbohydrates - General introduction and classification
Chemistry of carbohydrates - General introduction and classificationNamrata Chhabra
 
Protein misfolding diseases
Protein misfolding diseasesProtein misfolding diseases
Protein misfolding diseasesNamrata Chhabra
 
Protein structure, Protein unfolding and misfolding
Protein structure, Protein unfolding and misfoldingProtein structure, Protein unfolding and misfolding
Protein structure, Protein unfolding and misfoldingNamrata Chhabra
 
Molecular biology revision-Part 3 (Regulation of genes expression and Recombi...
Molecular biology revision-Part 3 (Regulation of genes expression and Recombi...Molecular biology revision-Part 3 (Regulation of genes expression and Recombi...
Molecular biology revision-Part 3 (Regulation of genes expression and Recombi...Namrata Chhabra
 
A quick revision of Carbohydrate metabolism with case- based discussions and ...
A quick revision of Carbohydrate metabolism with case- based discussions and ...A quick revision of Carbohydrate metabolism with case- based discussions and ...
A quick revision of Carbohydrate metabolism with case- based discussions and ...Namrata Chhabra
 

Más de Namrata Chhabra (20)

Applications of Recombinant DNA Technology
Applications of Recombinant DNA Technology Applications of Recombinant DNA Technology
Applications of Recombinant DNA Technology
 
Recombinant DNA Technology- Part 1.pdf
Recombinant DNA Technology- Part 1.pdfRecombinant DNA Technology- Part 1.pdf
Recombinant DNA Technology- Part 1.pdf
 
Polymerase Chain Reaction- Principle, procedure, and applications of PCR
Polymerase Chain Reaction- Principle, procedure, and applications of PCRPolymerase Chain Reaction- Principle, procedure, and applications of PCR
Polymerase Chain Reaction- Principle, procedure, and applications of PCR
 
Clinical case discussions
Clinical case discussions Clinical case discussions
Clinical case discussions
 
Basal metabolic rate (BMR)- Factors affecting BMR, measurement and clinical s...
Basal metabolic rate (BMR)- Factors affecting BMR, measurement and clinical s...Basal metabolic rate (BMR)- Factors affecting BMR, measurement and clinical s...
Basal metabolic rate (BMR)- Factors affecting BMR, measurement and clinical s...
 
Selenium- chemistry, functions and clinical significance
Selenium- chemistry, functions and clinical significanceSelenium- chemistry, functions and clinical significance
Selenium- chemistry, functions and clinical significance
 
Copper metabolism
Copper metabolismCopper metabolism
Copper metabolism
 
Folic acid- Chemistry, One carbon metabolism and megaloblastic anemia
Folic acid- Chemistry, One carbon metabolism and megaloblastic anemiaFolic acid- Chemistry, One carbon metabolism and megaloblastic anemia
Folic acid- Chemistry, One carbon metabolism and megaloblastic anemia
 
Biotin
BiotinBiotin
Biotin
 
Vitamin B12-Chemistry, functions and clinical significance
Vitamin B12-Chemistry, functions and clinical significanceVitamin B12-Chemistry, functions and clinical significance
Vitamin B12-Chemistry, functions and clinical significance
 
Sugar derivatives and reactions of monosaccharides
Sugar derivatives and reactions of monosaccharidesSugar derivatives and reactions of monosaccharides
Sugar derivatives and reactions of monosaccharides
 
Chemistry of carbohydrates part 2
Chemistry of carbohydrates part 2 Chemistry of carbohydrates part 2
Chemistry of carbohydrates part 2
 
Chemistry of carbohydrates - General introduction and classification
Chemistry of carbohydrates - General introduction and classificationChemistry of carbohydrates - General introduction and classification
Chemistry of carbohydrates - General introduction and classification
 
ELISA- a quick revision
ELISA- a quick revisionELISA- a quick revision
ELISA- a quick revision
 
Protein misfolding diseases
Protein misfolding diseasesProtein misfolding diseases
Protein misfolding diseases
 
Protein structure, Protein unfolding and misfolding
Protein structure, Protein unfolding and misfoldingProtein structure, Protein unfolding and misfolding
Protein structure, Protein unfolding and misfolding
 
Molecular biology revision-Part 3 (Regulation of genes expression and Recombi...
Molecular biology revision-Part 3 (Regulation of genes expression and Recombi...Molecular biology revision-Part 3 (Regulation of genes expression and Recombi...
Molecular biology revision-Part 3 (Regulation of genes expression and Recombi...
 
Enzymology quiz
Enzymology quizEnzymology quiz
Enzymology quiz
 
A quick revision of Carbohydrate metabolism with case- based discussions and ...
A quick revision of Carbohydrate metabolism with case- based discussions and ...A quick revision of Carbohydrate metabolism with case- based discussions and ...
A quick revision of Carbohydrate metabolism with case- based discussions and ...
 
Cancer
CancerCancer
Cancer
 

Último

M-2- General Reactions of amino acids.pptx
M-2- General Reactions of amino acids.pptxM-2- General Reactions of amino acids.pptx
M-2- General Reactions of amino acids.pptxDr. Santhosh Kumar. N
 
What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?TechSoup
 
Human-AI Co-Creation of Worked Examples for Programming Classes
Human-AI Co-Creation of Worked Examples for Programming ClassesHuman-AI Co-Creation of Worked Examples for Programming Classes
Human-AI Co-Creation of Worked Examples for Programming ClassesMohammad Hassany
 
Patterns of Written Texts Across Disciplines.pptx
Patterns of Written Texts Across Disciplines.pptxPatterns of Written Texts Across Disciplines.pptx
Patterns of Written Texts Across Disciplines.pptxMYDA ANGELICA SUAN
 
In - Vivo and In - Vitro Correlation.pptx
In - Vivo and In - Vitro Correlation.pptxIn - Vivo and In - Vitro Correlation.pptx
In - Vivo and In - Vitro Correlation.pptxAditiChauhan701637
 
Quality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICEQuality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICESayali Powar
 
Practical Research 1 Lesson 9 Scope and delimitation.pptx
Practical Research 1 Lesson 9 Scope and delimitation.pptxPractical Research 1 Lesson 9 Scope and delimitation.pptx
Practical Research 1 Lesson 9 Scope and delimitation.pptxKatherine Villaluna
 
How to Show Error_Warning Messages in Odoo 17
How to Show Error_Warning Messages in Odoo 17How to Show Error_Warning Messages in Odoo 17
How to Show Error_Warning Messages in Odoo 17Celine George
 
Presentation on the Basics of Writing. Writing a Paragraph
Presentation on the Basics of Writing. Writing a ParagraphPresentation on the Basics of Writing. Writing a Paragraph
Presentation on the Basics of Writing. Writing a ParagraphNetziValdelomar1
 
How to Add a many2many Relational Field in Odoo 17
How to Add a many2many Relational Field in Odoo 17How to Add a many2many Relational Field in Odoo 17
How to Add a many2many Relational Field in Odoo 17Celine George
 
How to Use api.constrains ( ) in Odoo 17
How to Use api.constrains ( ) in Odoo 17How to Use api.constrains ( ) in Odoo 17
How to Use api.constrains ( ) in Odoo 17Celine George
 
Education and training program in the hospital APR.pptx
Education and training program in the hospital APR.pptxEducation and training program in the hospital APR.pptx
Education and training program in the hospital APR.pptxraviapr7
 
Easter in the USA presentation by Chloe.
Easter in the USA presentation by Chloe.Easter in the USA presentation by Chloe.
Easter in the USA presentation by Chloe.EnglishCEIPdeSigeiro
 
The basics of sentences session 10pptx.pptx
The basics of sentences session 10pptx.pptxThe basics of sentences session 10pptx.pptx
The basics of sentences session 10pptx.pptxheathfieldcps1
 
Patient Counselling. Definition of patient counseling; steps involved in pati...
Patient Counselling. Definition of patient counseling; steps involved in pati...Patient Counselling. Definition of patient counseling; steps involved in pati...
Patient Counselling. Definition of patient counseling; steps involved in pati...raviapr7
 
How to Manage Cross-Selling in Odoo 17 Sales
How to Manage Cross-Selling in Odoo 17 SalesHow to Manage Cross-Selling in Odoo 17 Sales
How to Manage Cross-Selling in Odoo 17 SalesCeline George
 
How to Add Existing Field in One2Many Tree View in Odoo 17
How to Add Existing Field in One2Many Tree View in Odoo 17How to Add Existing Field in One2Many Tree View in Odoo 17
How to Add Existing Field in One2Many Tree View in Odoo 17Celine George
 
How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17Celine George
 
HED Office Sohayok Exam Question Solution 2023.pdf
HED Office Sohayok Exam Question Solution 2023.pdfHED Office Sohayok Exam Question Solution 2023.pdf
HED Office Sohayok Exam Question Solution 2023.pdfMohonDas
 

Último (20)

M-2- General Reactions of amino acids.pptx
M-2- General Reactions of amino acids.pptxM-2- General Reactions of amino acids.pptx
M-2- General Reactions of amino acids.pptx
 
What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?What is the Future of QuickBooks DeskTop?
What is the Future of QuickBooks DeskTop?
 
Human-AI Co-Creation of Worked Examples for Programming Classes
Human-AI Co-Creation of Worked Examples for Programming ClassesHuman-AI Co-Creation of Worked Examples for Programming Classes
Human-AI Co-Creation of Worked Examples for Programming Classes
 
Patterns of Written Texts Across Disciplines.pptx
Patterns of Written Texts Across Disciplines.pptxPatterns of Written Texts Across Disciplines.pptx
Patterns of Written Texts Across Disciplines.pptx
 
In - Vivo and In - Vitro Correlation.pptx
In - Vivo and In - Vitro Correlation.pptxIn - Vivo and In - Vitro Correlation.pptx
In - Vivo and In - Vitro Correlation.pptx
 
Quality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICEQuality Assurance_GOOD LABORATORY PRACTICE
Quality Assurance_GOOD LABORATORY PRACTICE
 
Practical Research 1 Lesson 9 Scope and delimitation.pptx
Practical Research 1 Lesson 9 Scope and delimitation.pptxPractical Research 1 Lesson 9 Scope and delimitation.pptx
Practical Research 1 Lesson 9 Scope and delimitation.pptx
 
How to Show Error_Warning Messages in Odoo 17
How to Show Error_Warning Messages in Odoo 17How to Show Error_Warning Messages in Odoo 17
How to Show Error_Warning Messages in Odoo 17
 
Presentation on the Basics of Writing. Writing a Paragraph
Presentation on the Basics of Writing. Writing a ParagraphPresentation on the Basics of Writing. Writing a Paragraph
Presentation on the Basics of Writing. Writing a Paragraph
 
How to Add a many2many Relational Field in Odoo 17
How to Add a many2many Relational Field in Odoo 17How to Add a many2many Relational Field in Odoo 17
How to Add a many2many Relational Field in Odoo 17
 
Finals of Kant get Marx 2.0 : a general politics quiz
Finals of Kant get Marx 2.0 : a general politics quizFinals of Kant get Marx 2.0 : a general politics quiz
Finals of Kant get Marx 2.0 : a general politics quiz
 
How to Use api.constrains ( ) in Odoo 17
How to Use api.constrains ( ) in Odoo 17How to Use api.constrains ( ) in Odoo 17
How to Use api.constrains ( ) in Odoo 17
 
Education and training program in the hospital APR.pptx
Education and training program in the hospital APR.pptxEducation and training program in the hospital APR.pptx
Education and training program in the hospital APR.pptx
 
Easter in the USA presentation by Chloe.
Easter in the USA presentation by Chloe.Easter in the USA presentation by Chloe.
Easter in the USA presentation by Chloe.
 
The basics of sentences session 10pptx.pptx
The basics of sentences session 10pptx.pptxThe basics of sentences session 10pptx.pptx
The basics of sentences session 10pptx.pptx
 
Patient Counselling. Definition of patient counseling; steps involved in pati...
Patient Counselling. Definition of patient counseling; steps involved in pati...Patient Counselling. Definition of patient counseling; steps involved in pati...
Patient Counselling. Definition of patient counseling; steps involved in pati...
 
How to Manage Cross-Selling in Odoo 17 Sales
How to Manage Cross-Selling in Odoo 17 SalesHow to Manage Cross-Selling in Odoo 17 Sales
How to Manage Cross-Selling in Odoo 17 Sales
 
How to Add Existing Field in One2Many Tree View in Odoo 17
How to Add Existing Field in One2Many Tree View in Odoo 17How to Add Existing Field in One2Many Tree View in Odoo 17
How to Add Existing Field in One2Many Tree View in Odoo 17
 
How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17How to Make a Field read-only in Odoo 17
How to Make a Field read-only in Odoo 17
 
HED Office Sohayok Exam Question Solution 2023.pdf
HED Office Sohayok Exam Question Solution 2023.pdfHED Office Sohayok Exam Question Solution 2023.pdf
HED Office Sohayok Exam Question Solution 2023.pdf
 

Revision Molecular biology- Part 2

  • 1. Revision-Molecular Biology PART-2 Professor (Dr.) NAMRATA CHHABRA MHPE, MD, MBBS, FAIMER FELLOW PRINCIPAL-IN-CHARGE, PROFESSOR & HEAD, DEPARTMENT OF BIOCHEMISTRY SSR MEDICAL COLLEGE, MAURITIUS Transcription, Translation, Genetic code and Mutations Case studies and Multiple-choice questions
  • 3. DNA Transcription •The synthesis of an RNA molecule from DNA is called Transcription. • All eukaryotic cells have five major classes of RNA: ribosomal RNA (rRNA), messenger RNA (mRNA), transfer RNA (tRNA), small nuclear RNA and microRNA (snRNA and miRNA). •The first three are involved in protein synthesis, while the small RNAs are involved in mRNA splicing and regulation of gene expression.
  • 4. Similarities between Replication and Transcription The processes of DNA and RNA synthesis are similar in that they involve- (1) the general steps of initiation, elongation, and termination with 5' to 3' polarity; (2) large, multicomponent initiation complexes; and (3) adherence to Watson-Crick base- pairing rules. 412-Jan-21 Our Biochemistry- Namrata Chhabra
  • 5. Differences between Replication and Transcription (1) Ribonucleotides are used in RNA synthesis rather than deoxy ribonucleotides; (2) U replaces T as the complementary base pair for A in RNA; (3) A primer is not involved in RNA synthesis; (4) Only a portion of the genome is transcribed or copied into RNA, whereas the entire genome must be copied during DNA replication; and (5) There is no proofreading function during RNA transcription. 512-Jan-21 Our Biochemistry- Namrata Chhabra
  • 6. Template strand Except for T for U changes, coding strand corresponds exactly to the sequence of the RNA primary transcript, which encodes the (protein) product of the gene. 612-Jan-21 Our Biochemistry- Namrata Chhabra
  • 7. Transcription unit and Primary transcript 712-Jan-21 Our Biochemistry- Namrata Chhabra
  • 8. Bacterial DNA-Dependent RNA Polymerase The DNA-dependent RNA polymerase (RNAP) of the bacterium Escherichia coli exists as an approximately 400 kDa core complex consisting of- •two identical α subunits, •similar but not identical β and β ' subunits, and •an ω subunit and a •A sigma subunit (σ) •Beta is thought to be the catalytic subunit. 812-Jan-21 Our Biochemistry- Namrata Chhabra
  • 9. Bacterial DNA-Dependent RNA Polymerase • RNAP, a metalloenzyme, also contains two zinc molecules. • The core RNA polymerase associates with a specific protein factor (the sigma σ factor) that helps the core enzyme recognize and bind to the specific deoxynucleotide sequence of the promoter region to form the preinitiation complex (PIC) • Bacteria contain multiple factors, each of which acts as a regulatory protein. 912-Jan-21 Our Biochemistry- Namrata Chhabra
  • 10. Mammalian DNA-Dependent RNA Polymerases Mammalian cells possess three distinct nuclear DNA-Dependent RNA Polymerases • RNA polymerase I is for the synthesis of r RNA • RNA polymerase II is for the synthesis of m RNA and miRNA • RNA polymerase III is for the synthesis of tRNA/5S rRNA, snRNA 1012-Jan-21 Our Biochemistry- Namrata Chhabra
  • 12. Termination of transcription (contd.) •Beyond the hair pin, the RNA transcript contains a strings of Us, the bonding of Us to the corresponding As is weak. •This facilitates the dissociation of the primary transcript from DNA. 1212-Jan-21 Our Biochemistry- Namrata Chhabra
  • 13. Modifications of primary transcript of mRNA in prokaryotes Transcription and translation are coupled in prokaryotic cells 1312-Jan-21 Our Biochemistry- Namrata Chhabra
  • 14. Post Transcriptional modifications of Ribosomal RNA (r- RNA) • The 23S,16S, and 5S ribosomal RNAs of prokaryotes are produced form a single RNA precursor molecule • Cleavage and trimming are the mechanisms involved, • Similar modifications are observed in the processing of eukaryotic r-RNA. 1412-Jan-21 Our Biochemistry- Namrata Chhabra
  • 15. Post Transcriptional modifications of Transfer RNA(t- RNA) The extra nucleotides at both 5' and 3' ends of t- RNA are removed, an intron from the anticodon arm is removed, bases are modified and CCA arm is attached to form the mature functional t RNA. 1512-Jan-21 Our Biochemistry- Namrata Chhabra
  • 16. Post Transcriptional modifications of pre m- RNA •The addition of the Guanosine triphosphate (part of the cap is catalyzed by the nuclear enzyme guanylyl transferase. •Methylation of the terminal guanine occurs in the cytoplasm. and is catalyzed by guanine-7-methyl transferase. 1612-Jan-21 Our Biochemistry- Namrata Chhabra
  • 17. Post Transcriptional modifications of pre m- RNA 1712-Jan-21 Our Biochemistry- Namrata Chhabra
  • 18. Post Transcriptional modifications of Pre m RNA Introns are removed from the primary transcript in the nucleus, exons (coding sequences) are ligated to form the mRNA molecule 1812-Jan-21 Our Biochemistry- Namrata Chhabra
  • 19. Splicing of m-RNA 1912-Jan-21 Our Biochemistry- Namrata Chhabra
  • 20. Clinical significance of Splicing 1) Antibodies against snRNPs In systemic Lupus Erythematosus (SLE), an auto immune disease, the antibodies are produced against host proteins, including sn RNPs. • 2) Mutations at the splice site • Mutations at the splice site can lead to improper splicing and the production of aberrant proteins . • For example, some cases of Beta thalassemia are as a result of incorrect splicing of beta globin m- RNA due to mutation at the splice site. 2012-Jan-21 Our Biochemistry- Namrata Chhabra
  • 21. Biological significance of Splicing Tissue specific proteins are produced from the same primary transcript by alternative splicing 2112-Jan-21 Our Biochemistry- Namrata Chhabra
  • 22. Inhibitors of Transcription • Rifampicin- binds with Beta subunit of prokaryotic RNA polymerase, • It is an inhibitor of prokaryotic transcription initiation. • It binds only to bacterial RNA polymerase but not to eukaryotic RNA polymerases. • Therefore, Rifampicin is a powerful drug for treatment of bacterial infections. • Used for the treatment of tuberculosis and leprosy 2212-Jan-21 Our Biochemistry- Namrata Chhabra
  • 23. Mechanism of action of Actinomycin D • Actinomycin D- Intercalates with DNA strands • Actinomycins inhibit both DNA synthesis and RNA synthesis by blocking chain elongation. • They interact with G·C base pairs as they require the 2-amino group of guanine for binding. • Actinomycins are used as anticancer drugs 2312-Jan-21 Our Biochemistry- Namrata Chhabra
  • 24. Mitomycin and Alpha amanitin • Mitomycin- Intercalates with DNA strands • blocks transcription, • used as anticancer drug • Alpha amanitin is a molecule made from the “death cap” mushroom and is a known potent inhibitor RNA polymerase. • One single mushroom could very easily lead to a fast death in 10 days. • The mechanism of action is that alpha amanitin inhibits RNA polymerase –II at both the initiation and elongation states of transcription. 2412-Jan-21 Our Biochemistry- Namrata Chhabra
  • 25. Question-1 A promoter site on DNA : a) Transcribes repressor b) Initiates transcription c) Codes for RNA Polymerase d) Regulates termination e) Translates specific proteins 2512-Jan-21 Our Biochemistry- Namrata Chhabra
  • 26. Answer b) Initiates transcription 2612-Jan-21 Our Biochemistry- Namrata Chhabra
  • 27. Question 2 The removal of introns and subsequent self-splicing of adjacent exons occurs in some portions of primary ribosomal RNA transcripts. The splicing of messenger RNA precursor is : a) RNA catalyzed in the absence of proteins b) Self-splicing c) Carried out by spliceosomes d) Controlled by RNA polymerase e) Regulated by RNA helicase 2712-Jan-21 Our Biochemistry- Namrata Chhabra
  • 28. Answer c) Carried out by spliceosomes 2812-Jan-21 Our Biochemistry- Namrata Chhabra
  • 29. Question 3 In bacterial RNA synthesis, the function of factor Rho is to : a) Increase the rate of RNA synthesis b) Allow accurate initiation of transcription c) Participate in termination of transcription d) Allow the binding of RNA polymerase to the promoter 2912-Jan-21 Our Biochemistry- Namrata Chhabra
  • 30. Answer c) Participate in termination of transcription 3012-Jan-21 Our Biochemistry- Namrata Chhabra
  • 31. Question 4 Two couples present to the emergency room with severe nausea, vomiting, and diarrhea. One of the patients admits that she served a salad at a dinner party to which she had added a few mushrooms. With this information, it is likely that their symptoms are as a result of inhibition of: a) RNA Polymerase II b) RNA Polymerase I c) RNA splicing d) RNA Polyadenylation e) RNA Polymerase III 3112-Jan-21 Our Biochemistry- Namrata Chhabra
  • 32. Answer a) RNA Polymerase II 3212-Jan-21 Our Biochemistry- Namrata Chhabra
  • 33. Question 5 A second-year student isolates nucleic acids from the cell, and finds that some of the nucleic acids are pseudouridine and ribothymidine. Which type of nucleic acid might have been isolated? a) t RNA b) rRNA c) m RNA d) Sn RNA e) Mi RNA 3312-Jan-21 Our Biochemistry- Namrata Chhabra
  • 34. Answer a) t RNA 3412-Jan-21 Our Biochemistry- Namrata Chhabra
  • 35. Question 6 A 35-year-old female develops fever, night sweats, weight loss, and a blood-tinged cough. An infectious disease doctor prescribed Rifampicin. Which of the following enzymes is inhibited by Rifampicin? a) DNA-dependent DNA polymerase b) DNA-dependent RNA polymerase c) RNA-dependent DNA polymerase d) RNA-dependent RNA polymerase e) Reverse transcriptase 3512-Jan-21 Our Biochemistry- Namrata Chhabra
  • 36. Answer b) DNA-dependent RNA polymerase 3612-Jan-21 Our Biochemistry- Namrata Chhabra
  • 37. Question 6 Actinomycin D, is an inhibitor of transcription, which acts as by inhibiting- a) β- subunit of prokaryotic RNA polymerase b) Movement of RNA polymerase along the DNA template c) Sigma subunit of RNA polymerase d) Prokaryotic Topoisomerase II e) Prokaryotic helicase 3712-Jan-21 Our Biochemistry- Namrata Chhabra
  • 38. Answer b) Movement of RNA polymerase along the DNA template 3812-Jan-21 Our Biochemistry- Namrata Chhabra
  • 39. Question 7 The initial RNA produced during the translation of DNA to RNA, which contains both the coding exons and the non-coding introns, is known as which of the following? a) Amino acyl transfer RNA b) m RNA c) Ribosomal RNA d) Heterogeneous nuclear RNA e) Small nuclear RNA 3912-Jan-21 Our Biochemistry- Namrata Chhabra
  • 40. Answer d) Heterogeneous nuclear RNA 4012-Jan-21 Our Biochemistry- Namrata Chhabra
  • 41. Question 8 Which of the following processes is not involved in the post transcriptional processing of t-RNA? A) Attachment of poly A tail B) Trimming C) Splicing D) Attachment of CCA arm E) Base modification 4112-Jan-21 Our Biochemistry- Namrata Chhabra
  • 42. Answer A) Attachment of poly A tail 4212-Jan-21 Our Biochemistry- Namrata Chhabra
  • 43. Genetic code 4312-Jan-21 Our Biochemistry- Namrata Chhabra
  • 44. Genetic Code  Genetic code is a dictionary that corresponds with sequence of nucleotides and sequence of Amino Acids.  Words in dictionary are in the form of codons  Each codon is a triplet of nucleotides  64 codons in total and three out of these are Non Sense codons.  61 codons for 20 amino acids 4412-Jan-21 Our Biochemistry- Namrata Chhabra
  • 45. 4512-Jan-21 Our Biochemistry- Namrata Chhabra
  • 46. Genetic Code-Characteristics  Specificity- Genetic code is specific (Unambiguous)  A specific codon always codes for the same amino acid. e.g., UUU codes for Phenyl Alanine, it can not code for any other amino acid. 4612-Jan-21 Our Biochemistry- Namrata Chhabra
  • 47. Genetic Code-Universal Universal- In all living organism Genetic code is the same.  The exception to universality is found in mitochondrial codons where AUA codes for methionine and UGA for tryptophan, instead of isoleucine and termination codon respectively of cytoplasmic protein synthesizing machinery.  AGA and AGG code for Arginine in cytoplasm but in mitochondria they are termination codons. 4712-Jan-21 Our Biochemistry- Namrata Chhabra
  • 48. Genetic Code-Redundant Redundant- Genetic code is Redundant, also called Degenerate. Although each codon corresponds to a single amino acid, but a single amino acid can have multiple codons. Except Tryptophan and Methionine each amino acid has multiple codons. 4812-Jan-21 Our Biochemistry- Namrata Chhabra
  • 49. Genetic Code- Non-Overlapping and Non- Punctuated  All codons are independent sets of 3 bases.  There is no overlapping ,  Codon is read from a fixed starting point as a continuous sequence of bases, taken three at a time.  The starting point is extremely important, and this is called Reading frame. 4912-Jan-21 Our Biochemistry- Namrata Chhabra
  • 50. Non-Sense Codons  There are 3 codons out of 64 in genetic code which do not encode for any Amino Acid.  These are called termination codons or stop codons or nonsense codons. The stop codons are UAA, UAG, and UGA. They encode no amino acid. The ribosome pauses and falls off the mRNA. 5012-Jan-21 Our Biochemistry- Namrata Chhabra
  • 51. Initiator codon  AUG is the initiator codon in majority of proteins-  In a few cases GUG may be the initiator codon  Methionine is the only amino acid specified by just one codon, AUG. 5112-Jan-21 Our Biochemistry- Namrata Chhabra
  • 52. Wobbling phenomenon  The rules of base pairing are relaxed at the third position, so that a base can pair with more than one complementary base.  Some tRNA anticodons have Inosine at the third position.  Inosine can pair with U, C, or A. This means that we don't need 61 different tRNA molecules, only half as many are required. 52 t RNA (first base) m RNA (Third base) Base pairing C G Traditional A U Traditional U A Traditional U G Nontraditio nal G C Traditional G U Nontraditio nal I U Nontraditio nal I C Nontraditio nal I A Nontraditio nal 12-Jan-21 Our Biochemistry- Namrata Chhabra
  • 53. Question 9 The following are all characteristics of genetic code except: a. Universal b. Degenerate c. Non-overlapping d. Ambiguous 5312-Jan-21 Our Biochemistry- Namrata Chhabra
  • 54. ANSWER d. Ambiguous 5412-Jan-21 Our Biochemistry- Namrata Chhabra
  • 55. Question 10 Which of the following is the initiator codon ? a) AGG b) AUG c) AUC d) AUA e) AUU 5512-Jan-21 Our Biochemistry- Namrata Chhabra
  • 56. Answer b) AUG 5612-Jan-21 Our Biochemistry- Namrata Chhabra
  • 57. Question 10 Which statement about genetic code is most accurate? a) Information is stored as sets of dinucleotide repeats called codons b) The code is degenerate (more than one codon may exist for a single amino acid) c) Information is stored as sets of trinucleotide repeats called codons. d) There are 64 codons, all of which code for amino acids. e) The sequence of the codons that make up a gene exhibits an exact linear correspondence to the sequence of amino acids in the translated protein. 5712-Jan-21 Our Biochemistry- Namrata Chhabra
  • 58. Answer e) The sequence of the codons that make up a gene exhibits an exact linear correspondence to the sequence of amino acids in the translated protein. 5812-Jan-21 Our Biochemistry- Namrata Chhabra
  • 60. Translation • The pathway of protein synthesis is called Translation because the ‘language’ of the nucleotide sequence on the mRNA is translated into the language of the amino acid sequence. • The mRNA is translated from its 5’end to its 3’end , producing a protein synthesized from its amino terminal end to its carboxyl terminal end. 6012-Jan-21 Our Biochemistry- Namrata Chhabra
  • 61. Components required for Translation • Amino acids • Transfer RNA • Messenger RNA • Aminoacyl t RNA synthetase • Functionally competent ribosomes • Protein factors • ATP and GTP as a source of energy 6112-Jan-21 Our Biochemistry- Namrata Chhabra
  • 62. Steps of Protein Synthesis The process of protein synthesis is divided into 3 stages- - Initiation - Elongation - Termination 6212-Jan-21 Our Biochemistry- Namrata Chhabra
  • 63. Initiation- The small ribosomal subunit binds to Initiation Factor 3 (IF3).
  • 64. The small subunit/IF3 complex binds to the mRNA. Specifically, it binds to the sequence AGGAGG, known as the Shine-Delgarno sequence, which is found in all prokaryotic mRNAs. 6412-Jan-21 Our Biochemistry- Namrata Chhabra
  • 65. Meanwhile, the fmet tRNA binds to Initiation Factor 2 (IF2), which promotes binding of the tRNA to the start codon. 6512-Jan-21 Our Biochemistry- Namrata Chhabra
  • 66. The small subunit/IF3 complex scans along the mRNA until it encounters the start codon. The tRNA/IF2 complex also binds to the start codon. This complex of the small ribosomal subunit, IF3, initiator tRNA, and IF2 is called the initiation complex. 6612-Jan-21 Our Biochemistry- Namrata Chhabra
  • 67. At this point, the large ribosomal subunit joins in. A molecule of GTP is hydrolyzed, and the initiation factors are released. The ribosomal complex is now ready for protein synthesis. 6712-Jan-21 Our Biochemistry- Namrata Chhabra
  • 68. When the ribosome is assembled, two tRNA binding sites are created; these are designated 'P' and 'A' (P stands for peptidyl, A stands for amino acyl). The initiator tRNA is in the P site, and the A site will be filled by the tRNA with the anticodon that is complementary to the codon next to the start. (In this case, it is the tRNA that binds proline.) 6812-Jan-21 Our Biochemistry- Namrata Chhabra
  • 69. When the second tRNA base pairs with the appropriate codon in the mRNA, an enzyme called peptidyl transferase catalyzes the formation of a peptide bond between the two amino acids present (while breaking the bond between fmet and its tRNA).This activity is intrinsic to the 23S r RNA found in the large subunit. Since the r RNA catalyzes this process , it is referred to as the Ribozyme 6912-Jan-21 Our Biochemistry- Namrata Chhabra
  • 70. Elongation At this point, the whole ribosome shifts over one codon. This shift requires several elongation factors (not shown) and energy from the hydrolysis of GTP. The result of the shift is that the uncharged tRNA that was in the P site is ejected, and the tRNA that was in the A site is now in the P site. The A site is free to accept the tRNA molecule with the appropriate anticodon for the next codon in the mRNA. 7012-Jan-21 Our Biochemistry- Namrata Chhabra
  • 71. The next tRNA base pairs with the next codon, and peptidyl transferase catalyzes the formation of a peptide bond between the new amino acid and the growing peptide chain. 7112-Jan-21 Our Biochemistry- Namrata Chhabra
  • 72. Termination When a termination codon enters the A site, translation halts. This is because there is no tRNA with an anti codon that is complementary to any of the stop codons. 7212-Jan-21 Our Biochemistry- Namrata Chhabra
  • 73. Inhibitors of protein synthesis • The tetracyclines (tetracycline, doxycycline, demeclocycline, minocycline, etc.) block bacterial translation by binding reversibly to the 30S subunit and distorting it in such a way that the anticodons of the charged tRNAs cannot align properly with the codons of the mRNA. • Puromycin structurally binds to the amino acyl t RNA and becomes incorporated into the growing peptide chain thus causing inhibition of the further elongation. 7312-Jan-21 Our Biochemistry- Namrata Chhabra
  • 74. Inhibitors of protein synthesis • Chloramphenicol inhibits prokaryotic peptidyl transferase • Clindamycin and Erythromycin bind irreversibly to a site on the 50 s subunit of the bacterial ribosome thus inhibit translocation. • Diphtheria toxin inactivates the eukaryotic elongation factors thus prevent translocation. 7412-Jan-21 Our Biochemistry- Namrata Chhabra
  • 75. Post Translational Modifications The newly synthesized protein is modified to become functionally active. The various post translational modifications are as follows- -Trimming -Covalent Alterations a)Phosphorylation b) Glycosylation c) Hydroxylation d) Gamma carboxylation e) Isoprenylation -Protein degradation 7512-Jan-21 Our Biochemistry- Namrata Chhabra
  • 76. Post Translational Modifications Trimming removes excess amino acids. Phosphorylation may activate or inactivate the protein Glycosylation targets a protein to become a part of the plasma membrane or lysosomes or be secreted out of the cell Hydroxylation such as seen in collagen is required for acquiring the three-dimensional structure and for imparting strength Defective proteins or destined for turn over are marked for destruction by attachment of a Ubiquitin protein. Proteins marked in this way are degraded by a cellular component known as the Proteasome. 7612-Jan-21 Our Biochemistry- Namrata Chhabra
  • 77. Question 11 The initiation of translation in eukaryotes requires which of the following: a. Initiation factor (IF-2) b. Elongation factor (EF)-2 c. A 40-S ribosomal subunit d. Methionyl-tRNA (f Met). 7712-Jan-21 Our Biochemistry- Namrata Chhabra
  • 78. Answer c) A 40-S ribosomal subunit 7812-Jan-21 Our Biochemistry- Namrata Chhabra
  • 79. Question 12 Which of the following statements about prokaryotic translation is incorrect? a. Transcription and translation are simultaneous b. Initiation takes place with the help of Methionyl-tRNA (f Met) c. 20 S and 60 S subunits together form a ribosome of 80 S d. Chloramphenicol inhibits prokaryotic translation. 7912-Jan-21 Our Biochemistry- Namrata Chhabra
  • 80. Answer c. 20 S and 60 S subunits together form a ribosome of 80 S 8012-Jan-21 Our Biochemistry- Namrata Chhabra
  • 81. Question 13 Which of the following components is required in prokaryotic protein synthesis? a. Aminoacyl t RNA synthetase b. Helicase c. Topoisomerase d. Primase. 8112-Jan-21 Our Biochemistry- Namrata Chhabra
  • 82. Answer a) Aminoacyl t RNA synthetase 8212-Jan-21 Our Biochemistry- Namrata Chhabra
  • 83. Question 14 A 34-year-old female develops a nonproductive cough and a low-grade fever. The attending physician suspects Mycoplasma pneumonia and starts empirically with Erythromycin. Which of the following describes the mechanism of action of Erythromycin? a) Inhibits the 50S ribosomal subunit. b) Inhibits the initiation factor- 1(IF-1). c) Binds to shine Dalgarno sequence. d) Inhibits the incoming aminoacyl tRNA. 8312-Jan-21 Our Biochemistry- Namrata Chhabra
  • 84. Answer a) Inhibits the 50S ribosomal subunit 8412-Jan-21 Our Biochemistry- Namrata Chhabra
  • 85. Question 15 A -4-year-old girl has been brought to the Pediatric OPD with fever and cough that sounds like a “whoop”. The pediatrician learns that the child has not been properly immunized and has yet to receive Pertussis vaccination. The mechanism by which the pertussis toxin causes cell death is through the inhibition of: a. Translocase b. Peptidyl transferase c. Elongation factor (EF)-2 d. Aminoacyl t-RNA synthetase. 8512-Jan-21 Our Biochemistry- Namrata Chhabra
  • 86. Answer a. Translocase 8612-Jan-21 Our Biochemistry- Namrata Chhabra
  • 87. Question 16 An 18-year-old girl has been advised to start with Tetracycline for the treatment for her acne. Which of the following statements best describes the mechanism of action of Tetracycline? Tetracycline: a. binds reversibly to the 30S subunit and distorts it. b. inhibits prokaryotic Peptidyl Transferase c. inactivates the prokaryotic elongation factors d. structurally binds to the aminoacyl t RNA. 8712-Jan-21 Our Biochemistry- Namrata Chhabra
  • 88. Answer a. binds reversibly to the 30S subunit and distorts it. 8812-Jan-21 Our Biochemistry- Namrata Chhabra
  • 89. Question 17 A 34-year-old has reported to the Medical OPD with a high -grade fever, dry cough, headache, loss of appetite, and pain abdomen lasting from the past seven days. She has been diagnosed with typhoid fever, for which she has been started with Chloramphenicol. The drug acts by inhibiting prokaryotic : a. Translocase b. Peptidyl transferase c. Initiation factor (IF)-2 d. Aminoacyl t-RNA synthetase. 8912-Jan-21 Our Biochemistry- Namrata Chhabra
  • 90. Answer b. Peptidyl transferase 9012-Jan-21 Our Biochemistry- Namrata Chhabra
  • 91. Question 18 Immunoglobulins, hemoglobin, and collagen are modified post- translationally by the process of: a) Hydroxylation b) Subunit aggregation c) Methylation d) Trimming. e) Carboxylation 9112-Jan-21 Our Biochemistry- Namrata Chhabra
  • 92. Answer b) Subunit aggregation 9212-Jan-21 Our Biochemistry- Namrata Chhabra
  • 94. INTRODUCTION ● A mutation is a permanent change in the nucleotide sequence of a gene. ● Mutations may be either gross, so that large areas of chromosome are changed, ● or may be subtle with a change in one or a few nucleotides. Mutations Large scale Point mutations 94
  • 101. Mutagens ● Chemicals o Nitroso compounds o Hydroxylamine NH2OH o Base analogs o Simple chemicals (e.g. acids) ○ Alkylating & methylating agents (e.g. N- ethyl-N-nitrosourea (ENU) 101
  • 102. Mutagens ● Chemicals o Polycyclic aromatic hydrocarbons e.g. benzopyrenes o DNA intercalating agents (e.g. ethidium bromide) o DNA cross linker (e.g. platinum) o Oxidative damage caused by oxygen(O)radicals 102
  • 103. Mutagens ❖ Radiations ● Ultraviolet radiation (non-ionizing radiation) - excites electrons to a higher energy level. DNA absorbs ultraviolet light. Two nucleotide bases in DNA - cytosine and thymine-are most vulnerable to excitation that can change base- pairing properties. UV light can induce adjacent thymine bases in a DNA strand to pair with each other, as a bulky dimer. ● Ionizing radiation 103
  • 104. Mutagens ❖ Biological- ○ Viruses (DNA or RNA viruses) ○ Transposons 104
  • 105. Classification of point mutations Point mutations Substitution Insertion Deletion 105
  • 107. Insertional mutagenesis ● Insertions in the coding region of a gene may alter splicing of the mRNA (splice site mutation), or ● cause a shift in the reading frame (frame shift), both of which can significantly alter the gene product. 107
  • 108. A) Point mutations iii) Deletions remove one nucleotide from the DNA. Like insertions, these mutations can alter the reading frame of the gene. 108
  • 109. B) Large-scale mutations B) Large-scale mutations in chromosomal structure, including: Amplifications (or gene duplications) leading to multiple copies of all chromosomal regions, increasing the dosage of the genes located within them. 109
  • 111. B) Large-scale mutations c) Chromosomal Mutations: ○ Chromosomal translocations: interchange of genetic parts from nonhomologous chromosomes. ○ Interstitial deletions: an intra-chromosomal deletion that removes a segment of DNA from a single chromosome, thereby apposing previously distant genes. ○ Chromosomal inversions: reversing the orientation of a chromosomal segment. 111
  • 112. Effects of point mutations Single-base changes in the mRNA molecules may have one of several effects when translated into protein: 1. Silent mutations-There may be no detectable effect because of the degeneracy of the code. 2. This would be more likely if the changed base in the mRNA molecule were to be at the third nucleotide of a codon. 112
  • 113. Effects of point mutations (2) A missense effect will occur when a different amino acid is incorporated at the corresponding site in the protein molecule. This mistaken amino acid—or missense, depending upon its location in the specific protein— might be acceptable, partially acceptable, or unacceptable to the function of that protein molecule. Most single-base changes would result in the replacement of one amino acid by another with rather similar functional groups. This is an effective mechanism to avoid drastic change in the physical properties of a protein molecule. 113
  • 114. a) Acceptable Missense mutations ● The sequencing of a large number of hemoglobin mRNAs and genes from many individuals has shown that the codon for valine at position 67 of the chain of hemoglobin is not identical in all persons who possess a normally functional chain of hemoglobin. ● The codon changes by point mutation from GUU (of valine) to GAU of Aspartic acid in Hb Bristol. ● Similarly in Hb Sydney the codon changes from GUU to GCU for Alanine. ● Both Hb Bristol and Hb Sydney are normal Hb variants with normal oxygen carrying capacity. ● Thus these are acceptable mutations. 114
  • 115. Partially acceptable Missense mutations ● Clearly, this missense mutation hinders normal function and results in sickle cell anemia when the mutant gene is present in the homozygous state. ● The glutamate-to-valine change may be considered to be partially acceptable because hemoglobin S does bind and release oxygen, although abnormally. 115
  • 116. c) Unacceptable Missense Mutations ● The hemoglobin M mutations generate molecules that allow the Fe2+ of the heme moiety to be oxidized to Fe3+, producing methemoglobin. ● Here the single nucleotide change alters the properties of a protein to such an extent that it becomes non- functional. ● Hb M results from histidine to tyrosine substitution. ● Distal Histidine of alpha chain of Globin is replaced by Tyrosine. ● The codon CAU is changed to UAU with the resultant incorporation of Tyrosine and formation of MetHb. ● Met hemoglobin cannot transport oxygen. 116
  • 117. (3) A nonsense mutation A nonsense codon may appear that would then result in the premature termination of a peptide chain and the production of only a fragment of the intended protein molecule. The probability is high that a prematurely terminated protein molecule or peptide fragment will not function in its assigned role. 117
  • 118. (3) A nonsense mutation ● The codon UAC for Tyrosine may be mutated to UAA or UAG, both are stop codons. Beta Thalassemia is an example of nonsense mutation. ● In certain conditions as a result of mutational event the stop codon may be changed to normal codon (UAA to CAA) . ● This results in the elongation of protein to produce “Run on polypeptides”. The resultant protein is a functionally abnormal protein. 118
  • 119. Frameshift Mutations ● A frame shift mutation is a mutation caused by inserts or deletes of a number of nucleotides from a DNA sequence. ● Due to the triplet nature of gene expression by codons, the insertion or deletion can disrupt the reading frame, or the grouping of the codons, resulting in a completely different translation from the original. ● The earlier in the sequence the deletion or insertion occurs, the more altered the protein produced is. 119
  • 120. Triplet deletion A triplet deletion removes exactly one amino acid from the polypeptide ,the most common mutation in cystic fibrosis is Delta F508 (i.e. deletion of amino acid number 508 (a phenylalanine, F). 120
  • 121. Trinucleotide expansion ● The commonest inherited cause of mental retardation is a syndrome originally known as Martin-Bell syndrome. ● Patients are most usually male, have a characteristic elongated face and numerous other abnormalities including greatly enlarged testes. ● In 1969 the name of the syndrome was changed to the fragile X syndrome. 121
  • 122. Trinucleotide expansion ● The mutation was tracked down to a trinucleotide expansion in the gene now named FMR1 (Fragile site with Mental Retardation). ● A number of diseases have now been ascribed to trinucleotide expansions. ● These include Huntington's disease and Myotonic dystrophy. 122
  • 123. Gene deletions ● Alpha Thalassemia is an example of Gene deletion. ● The clinical manifestations are as per the number of genes deleted. 123
  • 124. Consequences of Mutations Harmful mutations ● Changes in DNA caused by mutation can cause errors in protein sequence, creating partially or completely non-functional proteins. ● To function correctly, each cell depends on thousands of proteins to function in the right places at the right times. ● When a mutation alters a protein that plays a critical role in the body, a medical condition can result. ● A condition caused by mutations in one or more genes is called a genetic disorder. 124
  • 125. Consequences of Mutations ● If a mutation is present in a germ cell, it can give rise to offspring that carries the mutation in all of its cells. ● This is the case in hereditary diseases. ● On the other hand, a mutation can occur in a somatic cell of an organism. ● Such mutations will be present in all descendants of this cell, and certain mutations can cause the cell to become malignant, and thus cause cancer. 125
  • 126. Consequences of Mutations Beneficial mutations ● A very small percentage of all mutations actually have a positive effect. ● These mutations lead to new versions of proteins that help an organism and its future generations better adapt to changes in their environment. ● For example, a specific 32 base pair deletion in human CCR5 (CCR5-Δ32) confers HIV resistance to homozygotes and delays AIDS onset in heterozygotes. ● The CCR5 mutation is more common in those of European descent. 126
  • 127. Question 19 Triple repeat sequence disease occurs in: a) Alzheimer’s disease b) Cystic fibrosis c) Ataxia telangiectasia d) Huntington’s chorea 12712-Jan-21 Our Biochemistry- Namrata Chhabra
  • 128. Answer d) Huntington’s chorea 12812-Jan-21 Our Biochemistry- Namrata Chhabra
  • 129. Question 20 Which of the following changes in mRNA (resulting form point mutation) would result in the synthesis of a protein identical to the normal protein? a. UCA – UAA b. UCA- CCA c. UCA- UCU d. UCA- ACA 12912-Jan-21 Our Biochemistry- Namrata Chhabra
  • 130. Answer c. UCA- UCU 13012-Jan-21 Our Biochemistry- Namrata Chhabra
  • 131. Question 21 A-58-year-old male has recently been diagnosed with hemochromatosis. He presents with bronze discoloration of the skin and is found to have elevated plasma glucose and ferritin levels. The physician finds that he is carrying a mutation where tyrosine is substituted for Cysteine of the HFE gene. This disease results from which of the following mutations? a. Silent b. Nonsense c. Missense d. Frameshift. 13112-Jan-21 Our Biochemistry- Namrata Chhabra
  • 132. Answer c. Missense 13212-Jan-21 Our Biochemistry- Namrata Chhabra
  • 133. Thank you 13312-Jan-21 Our Biochemistry- Namrata Chhabra