Question

cDNA probes are copies from the messenger RNA molecules with the help of

• A. Restriction enzymes
• B. Reverse transcriptase
• C. DNA polymerase
• D. Adenosine deaminase

Answer 1

The correct option is B Reverse transcriptase

cDNA is a DNA copy synthesized from mRNA. The enzyme used is reverse transcriptase, an RNA-dependent DNA polymerase isolated from a retrovirus. As with other polymerases, a short double-stranded sequence is needed at the 3' end of the mRNA which acts as a start point for the polymerase. This is provided by the poly(A) tail found at the 3' end of most eukaryotic mRNAs to which a short complementary synthetic oligonucleotide (oligo dT primer) is hybridized (polyT-polyA hybrid). Together with all 4 deoxynucleotide triphosphates, magnesium ions and at neutral pH, the reverse transcriptase synthesizes a complementary DNA on the mRNA template. The progress of synthesis can be monitored by incorporation of P${}^{32}$ radioactive nucleotides. So, cDNA probes are copies from the messenger RNA molecules with the help of reverse transcriptase and not with DNA polymerase, restriction enzymes, and adenosine deaminase.
So, the correct answer is option B.