Question

The enzyme reverse transcriptase is:
(A) RNA dependent RNA polymerase
(B) RNA dependent DNA polymerase
(C) DNA dependent DNA polymerase
(D) DNA dependent RNA polymerase

Answer 1

Hint: Reverse Transcription is the reversible process of the “Central dogma of molecular biology”. Here, the enzyme uses a single-stranded molecule to synthesize a double-stranded structure.

Complete answer: Reverse transcriptase is an enzyme found in retroviruses that converts RNA into a double-stranded DNA. The whole process is called Reverse transcription. In this process, a complementary strand of DNA called cDNA is made first, and then the cDNA is converted into RNA. Retroviral Reverse transcriptase has three sequential biochemical activities:
i. RNA dependent DNA polymerase activity.
ii. Ribonuclease H (RNase H).
iii. DNA-dependent DNA polymerase activity.
Reverse transcriptase is developed to amplify RNA targets (RNA viruses such as HIV, HCV and influenza virus). Essentially, this method entails an initial step of transcribing a portion of the RNA genome into complementary DNA (cDNA), which is then amplified through PCR (Polymerase Chain Reaction).
Hence, the correct answer is option B.

Additional information: The process of protein synthesis consists of two major steps:
Transcription:- Synthesis of mRNA on DNA.
Translation:- Synthesis of protein along mRNA.
‘Transcription’ is a process of transfer of genetic information from DNA to mRNA. The segment of DNA that takes part in transcription is called ‘Transcription Unit’. It has three components: promoter, Structural gene and the terminator.
Whereas, translation is the mechanism by which the triplet bases sequence of mRNA molecules are converted into a specific sequence of amino acids in a polypeptide chain. It occurs on the ribosomes.

Note: In Central Dogma, DNA codes for mRNA; which codes for protein. One known exception to the central dogma is exhibited by retroviruses (like HIV in humans). Retroviruses consist of the RNA genome within the protein shell that is enclosed by a lipid capsule. The retroviruses gene is composed of three genes namely; group-specific gene, polymerase gene and the envelope gene.