what is structure of dna in human?

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what is structure of dna in human? 

The double halide structure of DNA by James Watson & Francis Crick in 1953 (Noble Prize, 1962). The DNA structure us considered as a milestone in the era of modern biology.

1. The DNA is a right handed double helix. It consist of two polydeoxyriboneuclotides (stands) fisted around each other on a common axis.

2. The two strands are ant parallel, i.e. one strand runs in the 5’ to 3’ direction which the other in 3’ to 5’ direction.

3. The width (or diameter) if a double helix is 20 A (2nm).

4. Each term (pitch) of the helix is 34 A (3.4mn) with 10 pairs of nueclotides, each pairs placed at a distance of about 3.4 A (.

5. The back bone of DNA id hydrophilic up of sugar & phosphate and hydro phobic base present inside the DNA helix.

6. The two strands are complementary in their base pairing. They are Nitrogenous base Adenine joined to thymine by Double. H-bond (A=T) and cytosine joins Guanine by triple H-bond (C=G).

7. The complementary base pairing in DNA helix proves Chargaff rules. The content of adenine equal to thymine (A=T) and guanine equals to cytosine (G=C) but there % age vary species to species.

8. The double helixes of DNA contain wider major groups &narrow minor groves. The grooves main function interacts with protein.

Types of DNA:-

There are 3 types of DNA present in the cell of A, B& Z DNA.

	A Form	B Form	Z Form
Helical Sense	Right handed	Right handed	Left handed
Diameters	26 A	20 A	18 A
Base pair per helical turn	11	10.5	12
Helix rise per base pair	2.6 A	3.4A	3.7 A
.............	.............	.............	.............
Glycosyl bond conformation	Anti	Anti	Anti for pyramidine syn for purine
Conditions for DNA	75% relative humidity Na+, K+, Cs+     ions.	92% relative Humidity Low ion strength	Very high salt concentration.

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