Question
Reverse transcriptase is an enzyme that makes a complementary DNA copy of RNA in retroviruses. This DNA copy can then insert itself into
the genome of the host cell. Reverse transcriptase has a higher error rate than DNA polymerase, which results in more mutations in the DNA copy of the RNA. Reverse transcriptase is not typically used by eukaryotic cells for any function.
(a) Describe which nucleotides you would expect to find in the genome of a virus that uses reverse transcriptase.
(b) The human immunodeficiency virus (HIV) contains RNA as its genetic material. Reverse transcriptase inhibitors have been shown to be effective in slowing the replication of HIV. Explain why reverse transcriptase inhibitors have few side effects in eukaryotic cells.
(c) Predict the rate of mutation in a retrovirus compared to that of a DNA virus.
(d) Justify your prediction from part (c).
▶️Answer/Explanation
Ans:
(a) A virus that uses reverse transcriptase would have RNA as its
genetic material, so its genome would contain the nucleotides
adenine, cytosine, guanine, and uracil. (Thymine is not found in
RNA.)
(b) Eukaryotic cells contain DNA as their genetic material and do not
need to use reverse transcriptase to make a DNA copy of their
genetic material. Therefore, eukaryotic cells do not contain reverse
transcriptase. A reverse transcriptase inhibitor would have few, if
any, side effects on eukaryotic cells.
(c) Retroviruses would be expected to have a higher mutation rate than
that of DNA viruses.
(d) One reason why a retrovirus would be expected to have a higher
mutation rate than that of a DNA virus is because retroviruses use
reverse transcriptase to copy their genome. Reverse transcriptase is
less accurate and generates more mutations than DNA polymerase,
which would lead to a higher mutation rate in retroviruses.