CARBOHYDRATESCourse : B.Sc.(Biochem) sem II

Sub : Biomolecules I

Unit 1

Carbohydrates

• Carbohydrates are the major components of most plants.

• Plants make carbohydrates on their own through photosynthesis.

• Separated into two categories– Simple– Complex

Functions of Carbohydrates

• Main source of energy• Spare protein from being burned so it can be

used to build and repair• Dietary fiber can help lower blood cholesterol• Part of connective tissues, some hormones

and enzymes and genetic material.

Sources

• Grains (wheat, corn, etc)• Rice• Beans• Sugars– Honey– Cane sugar– Molasses

Nutrition of Carbohydrates

• Provide 4 calories per gram• Main source of body’s energy• Body uses carbs before calories from protein

and fat.

Characteristics of Carbohydrates

• Consist of carbon, hydrogen, & oxygen• Energy containing molecules• Some provide structure• Basic building block is a monosaccharide

(CH2O)n ; n = 3,5,6• Two monosaccharides form a

disaccharide

Monosaccharides - simple sugars with multiple OH groups. Based on number of carbons (3, 4, 5, 6), a monosaccharide is a triose, tetrose, pentose or hexose.

Disaccharides - 2 monosaccharides covalently linked. Oligosaccharides - a few monosaccharides covalently

linked. Polysaccharides - polymers consisting of chains of

monosaccharide or disaccharide units.

I (CH2O)n or H - C - OH

I

Carbohydrates (glycans) have the following basic composition:

Different Forms of Glucose

Three Monosaccharides

C6H12O6

Dehydration Synthesisof a Disaccharide

Formation of Disaccharides

Hydrolysis of a Disaccharide

Important Polysaccharides: Starch

• Consists of glucose subunits

• Plant energy storage molecule

• Glycogen is a very similar molecule in animals.

• Starch and glycogen can be digested by animals.

Important Polysaccharides: Cellulose

• Composed of glucose subunits

• Different bond formed than starch

• Structural component in plants

• Cannot be digested by animals

Glycogen, the glucose storage polymer in animals, is similar in structure to amylopectin.

But glycogen has more α(1→6) branches.

The highly branched structure permits rapid glucose release from glycogen stores, e.g., in muscle during exercise. The ability to rapidly mobilize glucose is more essential to animals than to plants.

H O

OH

H

OHH

OH

CH2OH

HO H

H

OHH

OH

CH2OH

H

O

HH H O

OH

OHH

OH

CH2

HH H O

H

OHH

OH

CH2OH

H

OH

HH O

OH

OHH

OH

CH2OH

H

O

H

O

1 4

6

H O

H

OHH

OH

CH2OH

HH H O

H

OHH

OH

CH2OH

HH

O1

OH

3

4

5

2

glycogen

REFERENCES:

Books:

1.Principles of Biochemistry by Lehninger

2.Biochemistry, U. Satyanarayan, Elsevier India publication