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Explain why adenine and thymine have double bond while cytosine and guanine have triple bond

Explain why adenine and thymine have double bond while cytosine and guanine have triple bond.

Answers

Irene
First of all, those bonds are hydrogen bonds. They are not very strong, and they break as the molecules get farther from each other or at a certain temperature.

Hydrogen bonds form between a hydrogen bond donor and a hydrogen bond acceptor. If we speak for the nucleic acid bases, here are the donors and acceptors:

Between Cytosine and Guanine, there are 3 pairs of acceptor-donor. Hydrogen of NH2 functions as donor, whereas oxygen atom right across functions as acceptor. You can apply the same for the others.

Between Thymine and Adenine, only 2 hydrogen bonds can form as the distance between 2 donors and 2 acceptors allows them to. Remember that, the distance whence a hydrogen bond can form is roughly around 2–4 Angström. Even though I can’t tell at the moment that what distance is between the oxygen and hydrogen of Thymine and Adenine, it is possible to have a look by computational tools. What we know is, they are too distant to form a hydrogen bond. Hence, 2 hydrogen bonds between the two.

Note: It is Thymine, not Thyamine. It may be confused with the vitamin B1, Thiamine.

Hope that helped!
Irene Linah answered the question on January 31, 2019 at 14:59

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