Molecular Basis of Inheritance

SALIENT FEATURES OF DNA

Gap-fill exercise

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1. DNA is made of two chains,where the backbone is constituted by sugar - phosphate , and the bases project inside.

2.The two chains have polarity. It means , if one chain has the polarity 5’-------> 3’ polarity, the other has
3’ 5’ polarity.

3. The bases in the two strands are paired through hydrogen bonds (H – bonds)forming base pairs ( bp). Adenine forms two H-bonds with Thymine from opposite strand and vice – versa. Similarly, Guanine is bonded with Cytisine with H-bonds. (As a result,always a purine comes opposite to a pyrimidine. This generates approximately uniform distance between the two strands of the helix)

4. The two chgains are coiled in a right – handed fashion. The pitch of the helix is 3.4nm and there are roughly in each turn.Consequently,the distance between a bp in a helixis approximately equal to 0.34 nm.

5. The plane of one base pair stacks over the other in double helix.This in addition to H-bonds, confers stability of the structures.