Question

A certain virus uses RNA as its genetic material. The nucleotides of the viral genome are: 5’- GAUUAUAUGUAUUUCGCAAAGGAA-3’. When this RNA is copied to DNA, the sequence of the first product will be: a.5’-GATTATATGTATTTCGCAAAGGAA-3’

b. 5’-AAGGAAACGCTTTATGTATATTAG-3’

c. 5’-TTCCTTTGCGAAATACATATAATC-3’

d. 5’-CTAATATACATAAAGCGTTTCCTT-3’

e. 5’-UUCCUUUGCGAAAUACAUAUAAUC-3’

*I thought the answer was a but the answer is c can you please explain*

Answer 1

Ans:- If you look at the RNA and when it is copied back to DNA, the DNA sequence will be reverse complementary. Let us understand this with a simple example

Let say the mRNA sequence is 5'- GACAGU-3'

Now it's DNA sequence will be 3'- CTGTCA-5'

Now, the DNA sequence can be written from

5'- ACTGTC-3'. This, sequence is the real DNA sequence that is copied from mRNA by reverse transcriptase enzymes.

Similarly, we can write the RNA sequence

5'-GAUUAUAUGUAUUUCGCAAAGGAA-3

Complementary DNA sequence of this RNA will be

3'-CTAATATACATAAAGCGTTTCCTT-5'

Now, this DNA sequence if you write from 5'-3' you will get the results

5'-TTCCTTTGCGAAATACATATAATC-3'

Thus, this matches with option C which is a correct answer.

Rest all the options are incorrect.

Option a is incorrect because you have just replaced U with T but this is not right. If you have RNA means it is synthesized from complementary DNA using template. Thus, the complementary DNA is the template.

Dear student if you find the answer convincing please do give the feedback.