NUCLEIC ACIDS

Nucleic acid :

1. Nucleic acid are also called secret of life or 

     Key of life, as these are important  biomol -

     ecules necessary for existence of life. 

2. It is found in nucleus as well as cytoplasm. 

3. It is a long chain polymers of nucleotides of 

    very high molecular weight. 

4. Nucleic acid are composed of C, H, O, P and 

    N. 

5. Nucleic acid are of two types -

    a) DNA (Deoxyribose nucleic acid) 

    b) RNA (Ribose nucleic acid)

A) DNA or Deoxyribose nucleic acid. 

- DNA is a double stranded, helical, high molecular weight, polymer compound. 

- DNA is the genetic material in all organisms expect some virus. 

• Chemical composition of DNA 

It consist of -

a) Deoxyribose sugar 

b) Nitrogen bases

c) phosphate group 

A) Deoxyribose sugar -

 • The sugar in DNA is pentose sugar containing five carbon atom and having molecular formula C5H10O4

• It contains one oxygen atom less than ribose suger hence called deoxyribose sugar. 

• It contains five membrane pentagonal ring containing four carbon atom and one oxygen atom

• Deoxyribose sugar has three OH group at 1,3

and 5 and H atom at 1,2,3,4  number of carbon atom

• In deoxyribose, hydroxyl group at carbon atom 2 is replaced by hydrogen. 

B) Nitrogenous bases :

• These are nitrogen containing complex organic compounds. 

• They are of two types - 

1) Purines

2) pyrimidines

1) purines -

• Large and double ring (Dicyclic) (nine -membrane) compound. They have nitrogen at 1,3,7,9 position. 

• They required more space on DNA. 

    eg. Adenine (A) 

          Guanine (G) 

2) Pyrimidines -

• Small and single ring (Monocyclic and 6 membered). They have nitrogen at 1 and 3 position. 

• Required less space 

      eg. Cytosine (C) 

            Thymine(T) 

C) Phosphate group -

•  Phosphate is present in the form of phosphoric acid (H3PO4) or PO(OH)3 in DNA

• It has two reactive OH group. 

• Only OH group take part in formation of phosphodiester bond 

• It is joined with -3 carbon of one sugar and 5 carbon of adjacent sugar. 

• Due to present of phosphoric acid  DNA is acidic in nature. 

B) RNA  or  ribose nucleic acid. 

• Ribose nucleic acid (RNA) is the nucleic acid containing ribose sugar (C5H10O5) . 

• RNA single stranded polynucleotide molecule

Having C5 and C3 ends. 

• Chemically it consist of ribose sugar, phosphoric acid and nitrogen bases. 

• RNA is heteropolimer, Macromole with four type of ribonucleotide and high molecular weight. 

It has two types- 

a) messenger RNA 

b) Ribosomal RNA 

C) Transfer RNA 

They are present in all organisms expect virus. 

A) m-RNA 

• The RNA which carries message for protein synthesis to ribosome called m-RNA 

• The name was proposed by  Jacob and Mondon in (1961). 

• It is about 75-3000 nucleotide long. 

• Molecular weight is about 5,00,000 Dalton. 

• At 5` end starting codon is AUG which start protein synthesis. At 3` ends termination codon or stop codon is UAA which do not code for any amino acid. 

B) r - RNA 

• The RNA which present in ribosomes called ribosomal RNA. It also called as insoluble RNA. 

• molecular weight ranges about 40,000 Dalton to over a million. 

• It contains 100-5000 bases. 

C) t- RNA 

• The RNA which transfer activated amino acid from cytoplasm to site of protein synthesis called t-RNA . 

• It contains 75 to 85 nucleotide. 

• It's molecular weight is about 25,000 - 30,000

Dalton.