Question

Write an essay on structure of DNA.

Answer 1

DNA (deoxyribonucleic acid) is a long polymer of deoxyribonucleotides and is the hereditary material in most organisms. Each nucleotide consists of deoxyribose sugar, a phosphate group and one nitrogenous base: adenine (A), guanine (G), cytosine (C) or thymine (T).

Watson–Crick double-helix model

1. DNA consists of two polynucleotide strands coiled around one another to form a double helix. The sugar–phosphate backbones lie on the outside, while the bases face inward.
2. The strands are antiparallel: one runs [5'→3'], and the other runs [3'→5']. Nucleotides along each strand are linked by phosphodiester bonds.
3. Bases pair specifically and complementarily: A pairs with T through two hydrogen bonds, while C pairs with G through three. Each pair therefore consists of one purine and one pyrimidine.
4. A complete turn of the helix is 3.4, nm and contains 10 base pairs. Adjacent base pairs are 3.4, nm apart, and the helix is about 2, nm wide.
5. The strands are complementary, so the sequence of one determines the sequence of the other. This arrangement also provides a basis for accurate copying during DNA replication.

The double-helical, antiparallel and complementary structure of DNA enables it to store, replicate and transmit hereditary information.