Significance of carbohydrates in nature, the general classification of carbohydrates, and classification & functions of monosaccharides

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

2. Carbohydrates

3. Carbohydrates

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).

9. Sugar derivatives with nitrogen, phosphorus and sulphur group

10. Functions of carbohydrates
1) Sources of energy, especially for
brain and Red blood cells.

11. Functions of carbohydrates
2) Storage form of energy
Glycogen, starch, inulin

12. Functions of carbohydrates
3) Form structural tissues
in plants and in
microorganisms

13. Functions of carbohydrates
4) Intermediates in the
biosynthesis of other basic
biochemical entities (fats and
proteins)

14. Functions of carbohydrates
5) Ribose and deoxyribose
sugars form part of the
structural framework of
RNA and DNA.

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

20. Aldoses

21. Ketoses

22. Summary of classification
Number of carbon atoms Aldose Ketose
3 (Trioses) Glyceraldehyde Dihydroxyacetone
4 (Tetroses) Erythrose Erythrulose
5 (Pentoses) Ribose, Arabinose,
Xylose
Ribulose, Xylulose
6 (Hexoses) Glucose, Galactose,
Mannose
Fructose
7(Heptoses) - Sedoheptulose

23. Biological significance of monosaccharides
• Monosaccharides are important fuel molecules as well as
building blocks for nucleic acids.

24. Vote

25. Vote

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.

31. Further reading
https://www.ourbiochemistry.com/

32. Reflection