Question

Retrovirus uses ________ to make complementary DNA from RNA.
a. DNA polymerase
b. Restriction endonuclease
c. Reverse transcriptase
d. Reverse polymerase

Answer 1

A retrovirus or RNA virus is a type of virus that inserts a copy of its RNA genome into the DNA of a host cell. Inside the cytoplasm of a host, the virus uses its own enzyme to produce complementary DNA from its RNA genome. The term retrovirus means it works backwards from the original way.

Complete answer:
Retroviruses have genetic material in the form of RNA rather than DNA. It belongs to the viral family Retroviridae. Retrovirus uses a special enzyme called reverse transcriptase to produce complementary DNA (cDNA) from its RNA genome which involves the following steps:

- Once the virus enters the host's cell, the RNA strand undergoes reverse transcription in the cytoplasm to produce DNA.
- The DNA is then incorporated into the host cell genome by the help of integrase enzymes.
- The virus then replicates as a part of the host cell's DNA. At this point the retroviral DNA is referred to as a provirus.
- The host cell treats the viral DNA as a part of its own genome.
- It then undergoes the usual transcription and translation process to express the gene carried by the virus. The information contained in the retroviral gene is used to generate corresponding protein.

DNA polymerase is an enzyme that synthesizes new DNA molecules from deoxy-ribonucleotides. This enzyme plays a significant role in DNA replication. It works by sliding along the single strand template of DNA reading its nucleotides bases and attaches new complementary DNA nucleotides to an existing strand of nucleotides.

Restriction endonuclease is an enzyme that recognizes specific nucleotide sequences in double-stranded DNA. It is also called restriction enzymes or molecular scissors because it cleaves DNA into fragments at or near specific sequences known as restriction sites. It is a major tool of biotechnologists.

Hence, the correct answer is option (C).

Note: Retrovirus or RNA virus have RNA as their genetic material. These include Rous Sarcoma Virus (RSV), Human Immuno-deficiency Virus (HIV) etc. The RNA of these viruses causes an infected cell to synthesize an unusual enzyme RNA – directed DNA polymerase or reverse transcriptase.