| Direction: Each of these questions contains two statements |
| Assertion [A] and Reason [R]. Each of these questions also has four alternative choices, any one of which is the correct answer. You have to select one of the codes [a], [b], [c] and [d] given below. |
| 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. |
A) Both A and Rare true and R is the correct explanation of A
B) Both A and R are true, but R is not the correct explanation of A
C) A is true, but R is false
D) A is false, but R is true
Correct Answer: A
Solution :
[a] Both A and R are true and R is the correct explanation of A. 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.
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