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All common activities of a living organism (bioactivity) involve reactions of certain organic compounds (mostly organic). Such compounds are called biomolecules. The important biomolecules are carbohydrates, lipids, proteins, vitamins, hormones, nucleic acids etc.They not only build up living system, but are also responsible for their growth, maintenance  and their ability to reproduction. 

The later part of 1950 resulted in classic advance in the knowledge of how living cells engage themselves with molecules such as carbohydrates additionally the metabolism of carbohydrates also became clarified. In Biochemistry Carbohydrates belong to basic category of chemical compounds.They are biological means of consuming energy or storing energy; other forms being via fat and protein. 

Complex carbohydrates are known as polysaccharides. Amino acids and Peptides link in a head-to-tail style, i.e. the molecules are bounded by ionic interactions and H-bonds involving α-amino and α-carboxylate groups. Further, from several crystal structures it was confirmed that head to tail arrangement is unaffected by presence of water molecules. However, in the hydrated cases the case is different. Proteins and carbohydrates are essential constituents of our food. These biomolecules interact with each other and constitute the molecular logic of life processes. In addition, some simple molecules like vitamins and mineral salts also play an important role in the functions. 

  • What are Carbohydrates? 

Carbohydrates are the source that we rely on mostly for energy. We can encounter carbohydrates at almost every turn of our daily lives. The paper which we use is largely cellulose; so too is the cotton of our clothes and wood of our houses. So, carbohydrates meet all our basic necessities. The mystery of the energy in human body completely rests on the source carbohydrates. 

Old Definition of carbohydrates
The group of compounds known as carbohydrates received their general name because of early observations that they often have the formula Cx(H2O)y - that is, they appear to be hydrates  of carbon.

The above definition could not survive long due to the following reasons:

A number of compounds such as rhamnose, (C6H12O5) and 2-deoxyribose (C5H10O4) are known which are carbohydrates by their chemical behaviour but cannot be represented as hydrates of carbon.

There are other substances like formaldehyde (HCHO, CH2O) and acetic acid [CH3COOH, C2 (H2O)2] which do not behave like carbohydrates but can be represented by the general formula, Cx(H2O)y.

New definition of carbohydrates
Carbohydrates are defined as polyhydroxy aldehydes or polyhydroxy ketones or substances which give these on hydrolysis and contain at least one chiral carbon atom. It may be noted here that aldehydic and ketonic groups in carbohydrates are not present as such but usually exist in combination with one of the hydroxyl group of the molecule in the form of hemiacetals and hemiketals respectively.

  • What are Amino Acids?

Amino acids are organic compounds of both, an amino group & carboxylic group. They are represented by general formula:


These amino acids are very important because they are the building blocks of protein. Protein is the natural polymer movingα - amino acids as monomer. With the exceptions of glycine. All the other amino acids have chiral carbon & have two optically active isomers. All naturally occurring amino acids are in L – series in which –NH2 group on the left and –OH group in the right as L – glyceraldehydes.


  • What are Proteins?

Proteins are formed by joining the carboxyl group of one amino to the α - amino group of another acid. The bond formed between two amino acids by the elimination of water molecules is called peptide linkage.

21_peptide linkage.JPG

The product formed by linking amino acid molecules through peptide linkage -CO - NH - is called a peptide. When two amino acids combined in this way the resulting product is called a dipeptide.


Peptide are further designated as tri, tetra or penta peptides accordingly as they contain three, four or five amino acid molecules, same or different. In a peptide the amino acid that contains the free amino group is called the N – terminal residue (written on L.H.S). The amino acid that contains the free carboxyl group is called the C – terminal residue (written on R.H.S).

1979_terminal residue.JPG

If a large number of α - amino acids (100 to 1000) are joined by peptide bonds the resulting polyamide is called polypeptide.


By convention a peptide having molecular weight upto 10,000 is called polypeptide. While a peptide having a molecular mass more than 10,000 is called a protein.

We will study about some of the biomolecules in detail under following topics

You can also refer to the following related links

Classification of Carbohydrates

JEE Organic Chemistry Syllabus

Reference books of Organic Chemistry

To read more, Buy study materials of Biomolecules comprising study notes, revision notes, video lectures, previous year solved questions etc. Also browse for more study materials on Chemistry here.


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