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MCAT Biology Question — Viruses

While viruses are incredibly simple structures composed of little more than a protein coat and some DNA, some viruses require enzymes to be packaged in with their genetic material. Human immunodeficiency virus (HIV) is an example of a retrovirus. In HIV, which of the following proteins must be packaged in with its nucleic acids in order to reproduce successfully?


A. DNA polymerase

B. Helicase

C. Reverse transcriptase

D. None of the above; HIV can utilize its host cell for all of the proteins or enzymes it needs.

Click for Explanation

C is correct. A retrovirus is a single-stranded RNA virus that is able to convert its RNA to DNA with the help of the enzyme reverse transcriptase.

A. DNA polymerase, incorrect, DNA polymerase is the enzyme that builds the new DNA strand during replication in the nucleus. HIV does not have any particular need for DNA polymerase, and in any case, the host cell contains this enzyme.

B. helicase, incorrect, helicase is the enzyme that unwinds the DNA double helix for replication. This choice is incorrect for a similar reason as choice A.

C. reverse transcriptase, correct.

D. incorrect. While this choice is tempting, note that HIV infects human cells. Human cells typically do not create DNA from RNA, so they would not be expected to contain reverse transcriptase. This enzyme, then, must be provided by HIV itself.

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