Chemistry of Carbohydrates

Carbohydrates:

Carbohydrate or Saccharide is a compound of carbon, hydrogen and oxygen. (usually in the proportion of water). They are polyhydroxy alcohols (OH) with active carbonyl groups which can be aldehyde (H-C=O) or keto (C=O) group. Carbohydrates in food are in immediate source of energy for the body. 1 g of carbohydrates yields 4 calories . 60%of our body energy is derived from carbohydrates.
Following are the dietary sources of carbohydrates:

1. Rice ,wheat ,potatoes has carbohydrates in the form of starch.
2. Honey contains carbohydrates in the form of fructose.
3. Milk is rich in lactose.
Sugars (carbohydrates) with at least one free aldehyde or keto group in their structures are reducing sugars.
Sugars which have no free active group (means carbonyl groups are engrossed in bond making) are known as non reducing sugars means they cannot be reduced.
Carbohydrates can be classified into:
 Monosaccharide, Disaccharide, Oligosaccharide, Polysaccharide.

MONOSACCHARIDES:

Monosaccharides are simple sugars which cannot be further hydrolyzed. Monosaccharides can be aldose or ketose. All monosaccharides are reducing sugars.

NO OF CARBON ATOMS	GENERIC NAME	ALDOSES	KETOSES
3	Triose	Glycerose	Dihydroxy Acetone
4	Tetrose	Erythrose	Erythrulose
5	Pentose	Ribose	Riboluse
6	Hexose	Glucose etc	Fructose

Important monosaccharides are:

1.Glyceraldehyde (reference sugar as all sugars are derived from it)
2.Dihydroxy Acetone (involved in glycolysis thus provide energy)
3.Ribose (important component of DNA, RNA)
4.Glucose (required by the body as it gives energy)
Among all carbohydrates, brain utilizes only glucose for its energy requirement. Normal blood glucose level during fasting is 800-100 mg and randomly it should be100 to 120mg.
If glucose level during fasting is 800-100 mg and randomly it should be 100 to 120 mg it is converted into glycogen and glycogen is stored in liver & muscles.
1. Galactose (present in lactose)
2.Fructose (sweetest of all sugars ) (it acts as a source of energy for spermatozoa).
DISACCHARIDES

DISACCHARIDES	MONOSACCHARIDES
Maltose(Fruit sugar)	Glucose+Glucose
Lactose(Milk sugar)	Glucose+Galactose
Sucrose(Cane sugar)	Glucose+Fructose

Important examples of disaccharides are:
1. Maltose (present in fruits)
Maltose can also be produced when salivary and pancreatic amylase act on starch.
2. Lactose (present in milk and intestine)
Bacteria can ferment lactose to lactic acid.
3. Sucrose (cane sugar or table sugar)

Oligosaccharides:

They are composed of few simple sugars. Upon hydrolysis they give 3 to 10 monosaccharide units. They are not important physiologically.

Polysaccharides:

They are composed of large number of simple sugars. They are all non reducing sugars. They are of 2 types

1.     Homopolysaccharides

2.     Heteropolysaccharides

HOMOPOLYSACCHARIDES:

They are polymers of same type of simple sugars.

EXAMPLES:

1.     Glycogen (acts as storage of glucose)

Also known as animal starch

2.     Starch (provides energy in plants)

3.     Dextrin (have sweet taste)

It is the hydrolytic product of starch

4.     Dextrane (used as alternate of plasma)

Its solutions are highly viscous

5.     Cellulose (it increases bulk of food and cleans away intestine)

HETERO OR MUCOPOLYSACCHARIDES:

They are polymers of different types of simple sugars. They are acid containing carbohydrates.

EXAMPLES:

1.     Hyaluronic acid (promote fertilization of ovum)

2.     Heparin (natural anticoagulant in liver, thymus, blood, spleen and lungs.