1. What is Watson and Crick’s Double Helix DNA Model?
Ans. According to Watson and Crick’s (1953) Model:
i) DNA is a double helical structure. Each helix is made of several nucleotides connected with eath other by phospodiester bonds linking the 3?-OH of one nucleotide with the 5?-OH of the other.
ii) Two strands get twisted in opposite directions (i.e. Each follows 3??5? direction from opposite end) around a central axis.
iii) The stands are held together by the pairing of the nucleotides in the form A=T and G?C.
iv) Double helical DNA is 20A° in diameter and each in turn consists of 10 base pairs covering distance of 340 A°.
2. What is the nature of DNA?
Ans. a) Spectral Absorption: UV light at 260 nm. Wave length is strongly absorbed.
b) Molecular Reaction: As a product of innumerable anions, acts with several +vely charged molecules.
c) Denaturation: Denatures on heating and renatures with cooling.
d) Replication: Semiconservative.
f) Mutation: Mutation can cause changes in it to lead evolution.