Question

Which of the following is the activity of reverse transcriptase?

• A. Synthesis of cDNA from mRNA
• B. Synthesis of cDNA from DNA
• C. Removal of 5' -$\text{PO}_4^-$
• D. Removal of single strand protrusion from the ends

Hint:

Remember that "Reverse" transcription goes against the central dogma flow. Instead of DNA $\rightarrow$ RNA, it converts RNA (mRNA) back into DNA (cDNA).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
Reverse transcriptase is an enzyme originally discovered in retroviruses.
It transcribes single-stranded RNA templates into double-stranded DNA, reversing the classical flow of genetic information (DNA $\rightarrow$ RNA).

Step 2: Detailed Explanation:
Let us analyze the catalytic functions of reverse transcriptase:
- In genetic engineering and molecular biology research, reverse transcriptase is used to synthesize complementary DNA (cDNA) from a messenger RNA (mRNA) template.
- This reaction requires a primer (such as an oligo-dT primer or random hexamers) and dNTPs.
- The enzyme displays three sequential activities:
1. RNA-dependent DNA polymerase activity (synthesizing the first cDNA strand from the mRNA template).
2. RNase H activity (specifically degrading the RNA strand of the resulting RNA-DNA hybrid).
3. DNA-dependent DNA polymerase activity (synthesizing the second, complementary DNA strand).
- Let us review the incorrect options:
- Removal of $5'$ phosphate: This is carried out by alkaline phosphatase enzymes.
- Removal of single-strand protrusions: This is performed by single-strand-specific nucleases, such as S1 nuclease or Mung Bean nuclease.
Therefore, the primary activity of reverse transcriptase is the synthesis of cDNA from mRNA.

Step 3: Final Answer:
The activity of reverse transcriptase is the synthesis of cDNA from mRNA.