A word biomolecule first used in 1901.  It means organic molecules present in living organisms. A major goal of biochemistry is to study the cellular processes of living organisms and how these processes relate to the functioning of organism. All living organisms are composed of biomolecule only.


Biomolecules can be defined as the organic macromolecules present in living organisms. They are also known as biogenic substance. Biomolecules composed of carbon, hydrogen, oxygen, nitrogen, sulphur and phosphorus. They are covalently bonded with each other. Biomolecules are chemical compound found in living organisms. They are the building blocks of life perform important function in living organisms. Biomolecules  itself produced by living organisms. Such includes macromolecules like carbohydrates, protein, lipids, Nucleic acid (RNA, DNA) as well as small molecules such as primary and secondary metabolites and natural products.


Biomolecules are classified in following categories:

a)      Carbohydrates

b)      Proteins

c)       Lipids

d)      Nucleic acid



·         Carbohydrates are hydrates of carbon. They are mainly composed of carbon, hydrogen and oxygen in 1:2:1 with the general formula Cn (H2O).

·         They are polyhydroxy aldehydes and ketones.

·         Carbohydrates called as saccharides in Greek sakcharon mean sugar or sweetness.

·         Cabohydrates are often called as sugars. They are the staff of life for most organisms.

·         They are the most abundant biomolecule based on mass.

·          Also serve as reserve food in plants and animals.

·         In plants and arthropods carbohydrates form the skeletal structure.

·         Important energy source required for various metabolic activities and the energy is derived by oxidation process.

·         Plants are richer in carbohydrates than animals.

·         Carbohydrates supplement heat and energy for various metabolic activities of cell.

·         Carbohydrates are the most abundant organic compound in living organisms.

·         They originate as products from CO2 and H2O by photosynthesis.

nco2+nh2o+( reducing agent and sunlight)                      ADP+ C6H12O6+Nco2

ADP +Pi                    ATP

ATP is a form of chemical energy used ina cell which act as fuel of metabolism in plants and animals through aerobic cellular respiration.

CnH2On+no2+Pi+oxidizing agent and energy from photon                         ATP+Nco2+nh2o

Carbohydrates are the class of organic compounds that are polyhydroxy aldehydes or polyhydroxy ketones. It includes such enzymes which convert complex substance into simple substance. On simple chemical transformations viz. hydrolysis, oxidation, reduction such enzyme convert complex sugar like starch, cellulose into simpler ones like glucose.

Cellulose is the most abundant organic compound on earth.

Carbohydrates can be categorized into two categories:

a)      Simple carbohydrates

Simple carbohydrates are categorized into two types: Monosaccharides and Disaccharides

b)      Complex carbohydrates

It includes Polysaccharides.


·         They are known as simple sugars which possess free aldehyde or ketone group.

·         Although they are simplest so they cannot be hydrolyzed further.

·         General formula is Cn(H2O)n.

·         Monosaccharides includesTriose, Tetrose, Pentose, Hexose,Heptose.

·         Common examples are Fructose, Erythrulose, Ribulose.

        Structure of D-Fructose



               HO- C-H

                  H- C-OH

                  H -C-OH





·         They are known as Compound sugar.

·         Oligosaccharides yield 2-10 molecules of same or different monosaccharide on hydrolysis.

·         Oligosaccharides includes Disaccharides which yields two molecule on hydrolysis whose general formula is Cn(H2O)n-1.

·         Disaccharides are Sucrose, Lactose, and Maltose.

·         Oligosaccharides also include Trisaccahrides and Tetrasaccharides which yields three or four molecule on hydrolysis.




They are also compound sugar which yields more than ten molecules of monosaccharides on hydrolysis.

Their general formula is C6H10O5.

Dependent on the type of molecule produce as a result of hydrolysis Polysaccharides is divided into two categories:

Ø  Homopolysaccharides

Ø  Heteropolysaccharides




In homopolysaccharides type monosaccharides are of same type on hydrolysis.

Eg: Starch, Glycogen, Cellulose, Pectin.

Structure of glycogen




Here monosaccharides are of different type on hydrolysis.

Eg: Hyaluronic  acid, Chondritin sulphate

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