- A polymer of deoxyribonucleotides.
- Length is defined as the number of nucleotides or nucleotide pairs present. This is the characteristic of an organism.
- Bacteriophage Ø x174 has 5386 nucleotides.
- Bacteriophage λ has 48502 base pairs.
- Escherichia coli has 4.6 x 106 base pairs.
- The haploid genome of human DNA is 3.3 x 109 base pairs.
Structure of polynucleotide chain
- A nucleotide has 3 components:
- A nitrogenous base,
- A pentose sugar &
- A phosphate group.
Nitrogenous bases are of two types:
- Purine: adenine and guanine
- Pyrimidine: cytosine, thymine, and uracil.
- Thymine is present in DNA and uracil is present in RNA. Thymine is 5-methyl uracil.
- Pentose sugar is deoxyribose sugar in DNA and ribose sugar in RNA. Ribose sugar has an additional OH group at 2′ position.
A nucleoside is a nitrogenous base linked to pentose sugar through an N-glycosidic linkage.
- A glycosidic bond is formed between C at 1st position of sugar and N at 1st position of pyrimidine / N at the 9th position of purine.
A nucleotide is formed by the linking of a phosphate group to the 5′ OH group of ribose sugar of the nucleoside by a phosphoester linkage.
|Adenosine/ Deoxyadenosine||Adenylic acid/ Deoxyadenylic acid|
|Guanosine/ Deoxyguanosine||Guanylic acid/ Deoxyguanylic acid|
|Cytidine/ Deoxycytidine||Cytidylic acid/ Deoxycytidylic acid|