m-RNA to C-DNA is made by
**Core Concept**
The process of converting mRNA into cDNA is a crucial step in various molecular biology techniques, including reverse transcription polymerase chain reaction (RT-PCR) and cDNA library construction. This process involves the synthesis of a complementary DNA (cDNA) copy of the original mRNA template.
**Why the Correct Answer is Right**
The conversion of mRNA to cDNA is achieved through the action of the enzyme reverse transcriptase. This enzyme reads the mRNA template and matches the incoming nucleotides to the base pairing rules of DNA, resulting in the synthesis of a complementary cDNA strand. The cDNA strand is then used as a template for subsequent PCR reactions or as a substrate for cloning and sequencing.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because it does not specify an enzyme or a process involved in the conversion of mRNA to cDNA.
**Option B:** This option is incorrect because it refers to the process of DNA replication, which involves the synthesis of a new DNA strand from a template DNA strand, rather than the conversion of mRNA to cDNA.
**Option C:** This option is incorrect because it refers to the process of DNA transcription, which involves the synthesis of a new RNA strand from a DNA template, rather than the conversion of mRNA to cDNA.
**Clinical Pearl / High-Yield Fact**
One important aspect of reverse transcription is that it is a key tool in the diagnosis and monitoring of viral infections, such as HIV, where the viral RNA is converted to cDNA for subsequent analysis.
**Correct Answer: D. Reverse Transcriptase. Reverse transcriptase is the enzyme responsible for converting mRNA to cDNA.**