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Definition, Classification, Structure, Functions - Nucleic acids - Biomolecules | 11th Biochemistry : Biomolecules

Chapter: 11th Biochemistry : Biomolecules

Nucleic acids - Biomolecules

Nucleic acids are biopolymers, essential to all known forms of life.

Nucleic acids

 

Nucleic acids are biopolymers, essential to all known forms of life.

 

1. Definition

 

Nucleic acids are the polymers of nucleotides. Nucleotides are made of three components:

·        5-carbon sugar

 

·        Nitrogenous base

 

·        Phosphate groups

 

2. Structure of nucleic acids:

 

Sugar unit:

If the sugar unit present in the nucleic acid is a ribose, then the polymer is called ribonucleic acid (RNA) and if the sugar is deoxyribose, then the polymer is deoxyribonucleic acid (DNA).


 

Nitrogen base:

Nucleic acids contain purine and pyrimidine bases. They are Adenine (A), Guanine (G), Cytosine(C), Thymine (T) and uracil(U).


 

Phosphate group:

In nucleic acids, sugar unit and nitorgenous base can combine to form a nucleoside, these nucleosides combine with a phosphate to form a nucleotide, which in turn polymerises to form nucleic acids.


 

3. Classification

Nucleic acids are classified into two types based on the ribose sugar.

 

a. Deoxyribonucleic acids (DNA)


The most important constituent of chromosome. DNA is a polymer of nucleotides containing 2-deoxyribose sugar and nitrogenous bases like Adenine (A), Guanine (G), Thymine (T) andCytosine(C).

 

b. Ribonucleic acids (RNA)

 

RNA is a polymer of nucleotides containing ribose sugar and nitrogenous bases like Adenine (A), Guanine (G), Uracil(U), and Cytosine(C).

 

There are three main classes of RNA molecules, they are

 

i. Messenger RNA (mRNA).    ii. Transfer RNA (tRNA)         iii. Ribosomal RNA (rRNA)

 

4. Functions of DNA and RNA:

 

·     The main function of nucleic acids is to store and transfer genetic information.

 

·     DNA controls the synthesis of RNA in the cell.

 

·     DNA transmits the genetic information to mRNA for the synthesis a specific protein.

 

·     RNA directs synthesis of proteins.

 

·     mRNA takes genetic message from DNA.

 

·     tRNA transfers activated amino acid, to the site of protein synthesis.

 

·     rRNA are mostly present in the ribosomes, and responsible for stability of mRNA.

 

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