Reverse transcriptase is an enzyme whose mission is: 1) Synthesize DNA from an RNA template. 2) Synthesize RNA from a DNA template. 3) Repair DNA lesions during replication. 4) Complete the metabolic pathways blocked by an enzyme deficiency. 5) Initiate transcription on double-stranded circular chromosomes.
The Correct Answer and Explanation is:
Correct Answer: 1) Synthesize DNA from an RNA template.
Explanation:
Reverse transcriptase is a specialized enzyme primarily found in retroviruses, such as the Human Immunodeficiency Virus (HIV). Its fundamental role is to synthesize DNA from an RNA template. This process is the reverse of the typical flow of genetic information described by the central dogma of molecular biology, which states that DNA is transcribed into RNA and then translated into protein. Reverse transcriptase defies this direction by transcribing RNA back into DNA, a process known as reverse transcription.
Retroviruses carry their genetic material in the form of single-stranded RNA. When a retrovirus infects a host cell, it releases its RNA genome into the cytoplasm. The reverse transcriptase enzyme then becomes active and begins to use the viral RNA as a template to synthesize complementary DNA (cDNA). This cDNA is then integrated into the host cell’s genome through the action of another viral enzyme called integrase. Once integrated, the viral DNA can be transcribed and translated by the host cell’s machinery, leading to the production of new viral particles.
This unique enzymatic activity is crucial for the replication cycle of retroviruses and has also been harnessed in molecular biology and biotechnology. For example, reverse transcriptase is used in the laboratory to convert mRNA into complementary DNA, which can then be amplified using techniques such as polymerase chain reaction (PCR). This application is valuable in gene expression studies, diagnostics, and the development of various biotechnological tools.
Reverse transcriptase does not synthesize RNA from DNA, repair DNA lesions, complete metabolic pathways, or initiate transcription. Its sole and defining function is the synthesis of DNA using RNA as a template, which is why option 1 is the correct choice.
