Carbohydrates

Carbohydrates serve as principal energy sources for the body.They are defined as polyhydroxyaldehyde or ketones or the substances which on hydrolysis yield either aldehyde or ketone.

Carbohydrates constitute the major (80% of dry weight) part in the plant

The carbohydrates which are sweet in taste are collectively known as sugars (mono saccharides & disaccharides); while those which are not sweet are called non sugars (poly saccharides).

Most of the naturally occurring carbohydrates have Dextrorotatory (D)-configuration.

Simple sugars containing an aldehyde group are called aldoses and those with a keto group are called ketoses.

General formula: (CH₂O) n

Reducing sugar: Sugars that contain free aldehyde or ketone group in open chain configuration can reduce cupric ions to cuprous ions and hence are called reducing sugar.

Test for reducing sugar: Fehling’s and Benedict’s test.

The most important carbohydrate occurring in animals is Glucose (aldohexose)

Fructose (Levulose)-fruit sugar-sweetest of all sugars

Galactose occurs in milk as component of milk sugar, lactose

Ribose( Pentose sugar) is found in every animal and plant cell.Its reduced form deoxyribose is found in DNA.

Glycosidic bond

• This is when two mono saccharide join to form a disaccharide.
• The reaction is similar to condensation.
• The reaction involves the water been given off.

• Sucrose (cane sugar/table sugar/beet sugar)
• Maltose(Malt sugar) is found during germination of starchy seeds.
• Sucrose & Maltose -C₁₂H₂₂O₁₁
• Lactose (Milk sugar)

Polysaccharides are complex carbohydrates formed by condensation of a number of mono saccharides (more than 10).

• Structurally,they are of 2 types:

Homo polysaccharides: Starch, Cellulose, Glycogen

Hetero polysaccharides:Chitin, Pectin, Hemi cellulose

• Functionally, they are of 3 types:

Storage

Structural

Muco polysaccharides

Starch

• Storage polysaccharide of plant cells.
• Composed of the glucose polymers (80%amylose +20%amylopectin).
• Amylose-The water soluble fraction which is linear polymer of α-D-glucose.
• Amylopectin- The water insoluble fraction which consists of branched chains of α-D-glucose.

Glycogen

• Major glucose storage molecule in animals (stored in liver and skeletal muscle).
• The liver reserve of glycogen is used to regulate blood glucose levels.

Dextran (In Yeast and Bacteria)

• Bacteria and yeasts store glucose as yet another type of polysaccharide called Dextran.
• Dextrans are also used as components of blood plasma substitutes (plasma expanders) and foodstuffs.
  

Inulin (Dahila Starch)

• A fructose polymer is used as a starch substitute in diabetics ‘dietary products.
• In addition, it serves as a test substance for measuring renal clearance

Cellulose

• Most abundant polysaccharide, indeed the most abundant organic molecule in the world.
• Structural polysaccharide, used to make plant cell walls.
• Β (1-4) polymer of D-glucose that can contain thousands of glucose monomers.
• Cellulose cannot be digested by animals because they do not produce an enzyme capable of cleaving the glycosidic linkage.

Chitin

• A homopolymer from1-4-linked N-acetyl glucosamine.
  
• It is the most important structural substance in insect and crustacean shells, and is thus the most common animal polysaccharide.
• Second most abundant organic molecule.
• It also occurs in the cell wall of fungi.

They are slime or mucilage producing heteropolysaccharides

eg: Pectins, Phycocolloids (ex:Agar-agar), Hyaluronic acid,Chondroitin sulphate,Keratan sulphate.

Pectins

• Polymer of galacturonic acid, arabinose, and galactose.
• It is a major constituent of middle lamella.
• During ripening of fruits, pectate of middle lamella braks due to which fruits become soft.