1. Tardigrade
  2. Question
  3. Biology
  4. Assertion (A) Adenine cannot pair with cytosine. Reason (R) Adenine and cytosine do not have complementarity between their respective hydrogen donor and hydrogen acceptor sites.

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Q. Assertion (A) Adenine cannot pair with cytosine.
Reason (R) Adenine and cytosine do not have complementarity between their respective hydrogen donor and hydrogen acceptor sites.

Molecular Basis of Inheritance

Solution:

Both Assertion and Reason are correct and Reason is the correct explanation of Assertion.
Adenine cannot pair with cytosine. Adenine pairs with thymine and cytosine pairs with guanine. This occurs because adenine pairs with thymine with two hydrogen bonds, i.e. have only two hydrogen donor / hydrogen acceptor sites whereas cytosine has three hydrogen donor / hydrogen acceptor sites. Thus, due to lack of complementarity between the hydrogen donor and hydrogen acceptor sites between adenine and cytosine, these cannot pair.