Sunday, August 21, 2011


What are carbohydrates?

- Sugars/saccharides

- Contains mainly C H and O

- General formula (CH2O)n where n> or = 3

Biological role of carbohydrates

- Energy metabolism

- Biological structural material

- Molecular recognition among cells

- As water trapping molecules

Types of carbohydrates

- Monosaccharides

· Basic sub unit of all carbs

· Cannot be hydrolyzed to small units

· Produced from CO2 and H2O via photosynthesis

· General formula (CH2O)n

- Disaccharides

· Formed by condensation of 2 units of mono

· Joined by covalent GLYCOSIDIC bonds

· Sucrose,Maltose,Lactose

- Oligosaccharides

· Short chain carbs

· 3-12 units of monos

· Joined by glycosidic bonds

· Most are joined with PROTEINS

· Blood group antigens

- Polysaccharides

· Long chained carbs

· Large number of mono units

· Form macromolecules/biopolymers

· 2 types

(a) Homopolysaccharides – Composed of similar mono units

Eg:- Starch,Cellulose,Chitin,Glycogen

(b) Heteropolysaccharides – Composed of different sub units

Eg:- Glycoproteins

Classification of monosaccharides

- Number of C

· 3-triose-Glyceraldehyde

· 4-tetrose-Erythrose

· 5-pentose-Ribose,Arabiose,Xylose

· 6-hexose-Glucose,Fructose,Galactose

· 7-heptose-Sedoheptose

· 8-octose-monooctulose

· 9-nonose-nuraminic acid

- Active group

· Aldose – Sugars with aldehyde group – Glyceraldehyde,Ribose,Glucose,Galactose

· Ketose – Sugars with ketone group – Fructose,Ribulose

Structural characteristics of monosaccharides

1) formation of ring structure

- Occur in monos with 5 or more C

- Two possible configurations

· Open/strait chain structure

· The closed ring structure

Configurations are inter changeable in SOLUTIONS

- Under physiological conditions they exist in ring form because it is more stable

- Two types of ring structures are possible

· 6 membered ring – pyranoses

· 5 membered ring – furanoses

- This depends on the reaction of keto/aldehyde group with OH

- The distribution of the forms depends on;

· The structure of the sugar

· pH

· Temperature

· Solvent

Haworth projection is a common way of representing cyclic structure of monosaccharides with a simple 3d perspective.

The groups below the plane of the ring in Haworth projections are equivalent to those on the right-hand side of a Fischer projection.

- The pyranose forms of the sugars are more stable than the furanose forms in solution.

2.) Formation of steroisomers

Sterioisomers have same molecular formula but different spatial arrangement

- 2 possible sterioisomers

- Atoms are arranged such that they are mirror images of each other

- They are not superimposable

- Such are called ENANTIOMERS

- Molecules capable of exsisting in non super imposable mirror images are CHIRAL MOLECULES

- 2 types of enantiomers are found in biological systems

· D form

· L form

- Only one form is dominant

· L – amino acids

· D – sugars

- A C atom with 4 different groups bonded to it is a chiral/asymmetric carbon

- * The chiral C furthest from the carbonyl group determines the configuration L or D of the sugar*

- OH group on the left is L-glucose and on the right D-glucose

3.) Asymetric of carbon

- Ring formation has resulted in an asymmetric center at the first C atom

- Resulting in formation of 2 configurations

- Depending on the orientation of the OH group

· Alpha

· Beta

- These have different properties

- But they are not mirror images of each other

- They are called ANOMERS

- Carbon 1 is referred to as the ANOMERIC CARBON ATOM

-** Monosacs undergo interconversion between Alpha and Beta forms through the open chain linear form as an intermediate state

This is called MUTAROTATION **


  1. nice one. I've never seen anybody using this strategy to study for exams before

  2. Thanks!I don't know really, even this strategy is not doing any good to my exams. :-/ I was never able to girawafy anything and now I know I'll never be able to either. sigh!