IMAT 2011 Q41 [DNA Sample]

In a DNA sample, the percentage of guanine present was 28%. What is the percentage of thymine in the sample?

A. 22%

B. 27%

C. 28%

D. 44%

E. 54%

First of all, as always, we MUST READ CAREFULLY the question. Some of the IMAT questions are all about understanding the problem, and not jumping to the answer. Make sure to read the WHOLE question carefully, answering it in your head before you go and check the answers.

What are we being asked to find? Let׳s analyze the question.

In a DNA sample , the percentage of guanine present was 28% . What is the percentage of thymine in the sample?

We have DNA, which contains Guanine , Cytosine, Adenine, Thymine, As we remember and should already know Guanine has three hydrogen bonds with cytosine NOT THYMINE! (this is the tricky part of the question)

Therefore, we can calculate our rations. Guanine is 28; therefore Cytosine is 28.

100%-28%-28% = 44%

But wait, this 44% is splitting in 1:1 with adenine and thymine, so we have 22% OF THYMINE,, therefore, the answer is A

This question is quite easy and should take you about 30 to solve, but make sure to take your time and READ the question carefully because one of the things Cambridge (the test writers) likes to do is to confuse the exam takers!