Chemistry of carbohydrates - General introduction and classification
1. Chemistry of carbohydrates
Namrata Chhabra
M.D., M.H.P.E.,FAIMER Fellow
Principal Incharge, Professor and Head,
Department of Biochemistry,
SSR Medical College,
Mauritius
4. Learning objectives
● What is the chemical nature of carbohydrates
● What are the functions of carbohydrates
● How can we classify carbohydrates
● Reflection
● Questions
5. Carbohydrates
○ Carbohydrates are the most abundant compounds found in
nature (cellulose: 100 billion tons annually)
○ They make up most of the organic matter on Earth because
of their extensive roles in all forms of life.
○ One of the four major classes of biomolecules along with
proteins, nucleic acids and lipids.
6. What are carbohydrates ?
● The term carbohydrate is derived from the French term : hydrate
de carbone, they are hydrates of carbon
● Compounds composed of C, H, and O
● Empirical formula (C. H2O)n , for example when n = 5 then
C5H10O5
● Not all carbohydrates have this empirical formula: e.g. sugar
derivatives deoxy sugars, amino sugars etc., do not follow this rule.
7. General characteristics of carbohydrates
● They have large number of hydroxyl groups (poly hydroxy)
● In addition they may contain-an aldehyde group (poly
hydroxy aldehydes) or a keto group (poly hydroxy ketones)
● Their derivatives may also contain nitrogen, phosphorus or
sulfur.
8. Polyhydroxy aldehydes or ketones
Carbohydrates are
polyhydroxy aldehydes or
polyhydroxy ketones
(polyalcohol aldehydes or
polyalcohol ketones).
15. Functions of carbohydrates
Carbohydrates are linked to
many proteins and lipids, where
they play key roles in mediating
interactions among cells and
interactions between cells and
other elements in the cellular
environment.
16. Classification of carbohydrates
1) Monosaccharides (monoses or glycoses)
Trioses, Tetroses, Pentoses, Hexoses
2) Oligosaccharides
Di, tri, tetra, penta, up to 9 or 10
Most important are the disaccharides
3) Polysaccharides or glycans
a) Homopolysaccharides
b) Heteropolysaccharides
17. Monosaccharides
● Also known as simple sugars
● Cannot be hydrolyzed further
● Sub classified either by the number of carbon atoms
● or
● by the nature of functional group-aldoses or ketoses
18. MONOSACCHARIDES - Classification
1-According to number of carbons they contain in their backbone structures-
It is a variable prefix followed by the suffix (-ose):
Trioses=3 Carbon,
Tetroses=4C,
Pentoses=5C,
Hexoses=6C,
Heptoses=7C
19. MONOSACCHARIDES - Classification
2- According to nature of reactive group - depending on
the presence of Aldehyde or keto group:
Aldose sugars e.g. glyceraldehyde
Ketose sugars e.g. dihydroxyacetone
26. Biological significance of monosaccharides
• Trioses- Glyceraldehyde and
dihydroxyacetone, in their
phosphorylated forms are
intermediates of glycolysis.
27. Biological significance of monosaccharides
• Tetroses are
intermediated of HMP
(Hexose monophosphate)
pathway, which is an
intermediate pathway of
glucose utilization
28. Biological significance of monosaccharides
● Pentoses form the structural components of glycoproteins,
nucleotides and nucleic acids.
● They also serve as intermediates in the HMP pathway.
29. Biological significance of monosaccharides
• Hexoses
o Glucose is an important fuel molecule preferred source
of energy for the brain cells and the only source of energy for
the red blood cells and the cells lacking mitochondria.
o Fructose- component of table sugar(Sucrose), honey
and source of energy for the spermatozoa
o Galactose- An important component of milk sugar
(Lactose)
o Mannose- An important component of glycoproteins.
30. Biological significance of monosaccharides
• Heptoses- Sedoheptulose is
an important intermediate of
HMP pathway
• Nonoses- Sialic acid is an
important component of
glycolipids.