Biology 9700 · AS & A Level · Structure of nucleic acids and replication of DNA

Structure of nucleic acids and replication of DNA — practice question

Human cytomegalovirus (HCMV) is a virus that commonly infects humans. In individuals with a fully working immune system, HCMV infection usually produces no symptoms, or only very mild ones. Fig. 2.1A shows a diagram of a section through HCMV. In Fig. 2.1B, only the external region of HCMV is sectioned.
(a)[2]

Structure S in Fig. 2.1A is one subunit of structure T in Fig. 2.1B. Name the chemical compound that forms structure S and name structure T.

(b)[1]

The actual diameter of the HCMV shown in Fig. 2.1 is $0.17\,\mu\text{m}$. Calculate the actual diameter of the virus in nanometres (nm) if this measurement is used.

(c)[1]

Suggest the role of viral DNA polymerase within the host cell.

(d)[2]

The virus in Fig. 2.1 is shown as a spherical form. Structure T always has the same shape. However, electron micrographs indicate that HCMV virions are not all identical in shape. Suggest how HCMV virions can have different shapes.

(e)[2]

With reference to Fig. 2.1A, State one similarity and one difference between the genetic material of HCMV and the genetic material of a typical bacterial cell.

(f)[3]

HCMV is known to infect some types of human cell that carry out the mitotic cell cycle. Studies have shown that when the tegument protein UL69 is present, the cell cycle stops in the G1 stage. Outline the effects the presence of UL69 will have on the normal activity of the mitotic cell cycle.

(g)[4]

After a person has been infected with HCMV, the virus stays dormant in the body for life. If it later becomes active again (reactivates), serious illness will only result if the person has a weak immune system at that time. Explain why the response to HCMV reactivation is more likely to cause serious illness in a person with a weak immune system.

Worked solution & mark scheme

This 15-mark question has a full step-by-step worked solution and mark scheme. One marking point: S is made of protein.

  • Full mark scheme, point by point
  • Step-by-step worked solution
  • Write your answer & get it marked instantly by AI