what is watson and crick model of DNA?
Answers
ANSWER:-
DOUBLE HELIX MODEL OF DNA:- (Watson and Crick model of DNA)
○ The molecular structure of DNA was first proposed by Watson and Crick.
○ Their double helix model of DNA was based on the following evidences:
1. Chargaffs Base Ratios:-
○ Chargaff and others studied the amount of each of the four nitrogen bases in DNA from different organism.
○ They observed that the concentration of thymine was always equal to the concentration of adenine and the concentration of guanine was equal to the concentration of cytosine.
○ This indicates that there is a definite relationship between the bases.
2. X-ray Analysis:-
○ Maurice Wilkins and Rosalind Franklin employed X-ray diffraction to analyse the structure of DNA.
○ According to their model, DNA exists as a double helix in which two polynucleotide chains are coiled about one another in a spiral.
○ Each polynucleotide chain consists of a sequence of nucleotides linked together by phophodiester bonds.
○ The two polynucleotides strands are held together in their helical configuration by hydrogen bonds between the bases of opposite strands.
○ The basepairing is specific i.e adenine pairs with thymine and cytosine pairs with guanine.
○ Adenine and thymine form two hydrogen bonds and cytosine and guanine form three hydrogen bonds.
○ If the base sequences of one strand of the helix is known, the base sequences of the other strand is also known because of the specific base pairing.
○ The two strands of DNA double helix is hence said to be complementary.
