Remember the researcher (from previous question) who was trying to clone and subsequently express the human histone H4 protein in the bacterium E. coli? She extracted the total available RNA from a sample of a human cell line (HEK cells). Her objective for the next step is to make a copy DNA (cDNA) strand using the mRNA of the human histone H4 protein as a template. Which one of the following enzymes will she need to successfully perform this step?

Question

BlackTom AI · Accepted Answer

The scenario asks which enzyme is required to synthesize a cDNA strand using mRNA as the template. This process is called reverse transcription, and the enzyme that carries it out is reverse transcriptase.

Option a: RNA transcriptase. This term is not a standard, widely recognized enzyme for cDNA synthesis. It could mislead students into thinking there is an enzyme dedicated to transcribing RNA into RNA, which would not produce DNA. The correct enzyme must produce DNA from an RNA template, which RNA transcriptase does not conventionally refer to.

Option b: DNA polymerase. While DNA polymerases synthesize DNA, they require a DNA template or a pre-existing DNA primer and cannot efficiently use an RNA template to make a complementary DNA strand. They are not the enzymes used to generate cDNA from mRNA.

Option c: Reverse transcriptase. This is the correct choice. Reverse transcriptase is an RNA-dependent DNA polymerase that uses mRNA as a template to synthesize complementary DNA (cDNA), enabling subsequent cloning or expression in bacteria.

Option d: Taq polymerase. Taq is a DNA polymerase used in PCR to amplify DNA, not to synthesize cDNA from RNA templates. It does not initiate cDNA synthesis from RNA and requires a DNA template.

In summary, to convert mRNA into cDNA, the enzyme of choice is reverse transcriptase, which specifically reads RNA and synthesizes complementary DNA, enabling downstream applications like cloning and expression in E. coli.

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