Question

You have discovered a new virus that contains only RNA as its genetic material. Curious as to how this virus works, you infect host cells with this virus and discover that after infection, the host cell makes lots of viral RNA molecules and various viral proteins. Upon further examination, you discover that the viral genome has been inserted into the host genome as DNA.

These are the steps of the information flow for this virus. Each arrow represents a process that is carried out by an enzyme.

RNA viral genome --> DNA --> RNA --> protein
Considering an actively-dividing, normal cell that carries the viral genome, indicate

whether the following statements are true or false for the virus discussed above.

You do NOT need to give reasoning or justification for your answer. Just answer true or false in your answer booklet.

Answer A, B, C, and D

A) RNA-dependent RNA polymerase is used at some point during the viral life cycle to copy the viral genome. (1.5 marks)

B) The polymerase used by the virus to copy its genome forms a covalent bond between a 5? phosphate and a 3? hydroxyl. (1.5 marks)

C) During copying of the viral genome, polymerization would proceed in the 3? --> 5?direction. (1.5 marks)

D) Deoxyribonucleotides would be incorporated into the viral genome that is inserted into the host chromosome.

Answer 1

A) False: RNA dependent DNA polymerase (reverse transcriptase) is used by virus to convert its genetic material i.e. RNA into DNA. The later is then incorporated into the genome of host.

B) True: A phosphodiester bond is formed between the 3' carbon atom of one sugar molecule and the 5' carbon atom of another by covalent binding of a 3? hydroxyl group of one nucleotide to 5? phosphate of another nucleotide.

C) False: In polymerisation reaction, 3? hydroxyl group acts as a nucleophile which attacks on  5? phosphate of incoming nucleotide. So, polymerisation always takes places in 5? --> 3? direction. Same is true with the viral genome that is that is copied in form of DNA.

D) True: the insertion of viral genome into the host chromosome will be only after it is reverse transcribed to DNA. So, after insertion it will be present as DNA and will contain deoxyribonucleotides rather than ribonucleotides.