question_answer

The table shows the result of an analysis of percentage concentration of three bases in nucleic acids from four sources. Three of the sources are DNA and one is RNA. Which source is RNA?

A)

Source	Adenine	Cytosine	Guanine
A	19.7	30.4	30.2

B)

Source	Adenine	Cytosine	Guanine
B	25.5	24.6	23.8

C)

Source	Adenine	Cytosine	Guanine
C	26.7	28.8	22.3

D)

Source	Adenine	Cytosine	Guanine
D	31.1	18.3	18.7

Correct Answer: C

Solution :

In the DNA molecule, the width between the 2 backbones is equal to the width of 1 base pair, i.e. 1 purine and 1 pyrimidine.

In DNA, the bases pair with complementary bases of the opposite chain via hydrogen bonds, adenine to thymine and cytosine to guanine.

Thus, the number of \[G=C,\]number of\[A=T\].

Hence, when the percentage concentration of cytosine is similar to guanine, this suggests that source is DNA.