Why do you think adenine does not basepair with cytosine and

Why do you think adenine does not base-pair with cytosine; and why thymine does not base-pair with guanine? Suggested length: 1 or 2 paragraphs.

There are 2 types of nitrogenous base - purine and pyrimidine.

Purine - Adenine , Guanine

Pyrimidine - Thiamine, Cytosine.

In general , purine and pyrimidine do not pair with themselves. There are few reasons for this occurence :

1. Distance of pyrimidine from each other. For them to pair with each ither they need to come closer.

2. Purines have big sizes so they are not able.to fit into the helix.

A and T are linked by 2 hydrogen bonds whereas G. And C is linked by 3 hydrogen bonds.

This pairing is generally on the basis of chargaff\'s rule according to which

A+G = C +T