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Carbohydrates

Carbohydrates Essential structural components of living cells and source of energy for animals. Carbohydrates are essential in formation of amino acids and fatty acids.
Composition

Carbohydrates are composed of Carbon, Hydrogen and Oxygen. 

Hydrogen and Oxygen are composed in the same ratio as water(2:1).
Types

Carbohydrates are broadly classified into two groups,

  1. Monosaccharides(Simple carbohydrates or simple sugars) with small molecules.

Major monosaccharides:

Sugar Source
Glucose Occurs naturally in several forms in many food sources. e.g. dextrose.
Galactose Milk .
Fructose Found in honey and in many ripe fruits.

Glucose is absorbed directly by the body, without any breakdown. Galactose and fructose are converted into glucose by liver, before their utilization by body cells. 

Surplus glucose is converted and stored in the form of glycogen and fat by liver, muscles, and fat cells.

Hydrolysis breaks glycogen to form glucose monomers.

  1. Polysaccharides(Complex carbohydrates or Starches) are polymers formed by combination of monosaccharides through covalent bonds. Polysaccharides are insoluble in water.

Polysaccharides either serve as storage material(glycogen) or forms building material(cellulose, chitin etc..) for organisms' structures.

Oligosaccharides: carbohydrates containing between two and ten monosaccharide units linked together.

Disaccharides(double sugars) -  formed by combination of two monosaccharides joined by a covalent bond.

Major disaccharides:

Disaccharide Source
Sucrose Cane, Beet and many other plants.
Maltose Formed by the action of malt or diastase on starch.
Lactose One glucose molecule linked to a galactose molecule. Found only in milk.

These complex sugars are broken down into simple sugars before their absorption.
Dietary sources Fruits, cereals and all starch foods.