DNA synthesized from an RNA template is called
- (A)
recombinant DNA.
- (B)
transcript.
- (C)
T-DNA.
- (D)
complementary DNA.
GATE 2020 BT Q.7: solution and answer
Answer and solution
ANSWER
The correct answer is (D) complementary DNA (cDNA).
Official answer: DSource: Official answer key, GATE 2020 BT (IIT Delhi)
The question asks: what is DNA synthesized from an RNA template called?
(A) Recombinant DNA is wrong: this term refers to DNA made by joining fragments from different sources in vitro using restriction enzymes and ligase — it has nothing to do with copying an RNA template.
(B) Transcript is wrong: a transcript is RNA synthesized from a DNA template (transcription), which is the reverse information flow from what the question describes.
(C) T-DNA is wrong: T-DNA (transfer DNA) is the segment of the Ti plasmid of Agrobacterium tumefaciens that is transferred into plant cells during genetic transformation; it is unrelated to RNA-templated DNA synthesis.
(D) Complementary DNA (cDNA) is correct: the enzyme reverse transcriptase (an RNA-dependent DNA polymerase) synthesizes a DNA strand complementary to an RNA template (such as mRNA), and this DNA product is, by definition, called cDNA.
Therefore the correct answer is (D) complementary DNA.
KEY IDEA
Reverse transcriptase synthesizes DNA using an RNA template; this DNA product is called complementary DNA (cDNA).
WATCH OUT FOR
Confusing the direction of information flow — thinking "transcript" (RNA made from DNA) is the same process reversed, or confusing cDNA with recombinant DNA (which is made by joining DNA fragments from different sources, not by copying RNA).
From the GATE 2020 BT paper. Every question of this paper · Download the full paper · All 5 Libraries & cloning questions, with notes