Viruses

Question 1

Virus structure

Answer 1

Core of genetic material (RNA or DNA), surrounded by protein capsid, lipid envelope* (from previous host cell) and attachment proteins

Question 2

Viral replication process

Answer 2

• Virus attachment proteins bind to complementary receptor proteins on cell membrane of the host cell
• Nucleic acid released into host cell
• Reverse transcriptase to make complementary strand of DNA from viral RNA template
• DNA inserted into cell DNA, transcribed into viral mRNA, translated into viral proteins
• Capsid reforms
• Viral particles assemble and released from host cell

Question 3

HIV (human immunodeficiency virus)

Answer 3

• Infects and kills T-helper cells
• Immune system becomes weak, and AIDS (acquired immune deficiency syndrome) develops

Question 4

Symptoms of AIDS

Answer 4

• Initial flu-like symptoms until latency period
• Initial minor infections of mucous membranes, recurring respiratory infections
• Progressively more susceptible to serious infections (eg. Tuberculosis)
• Later development of serious infections (eg. Toxoplasmosis of the brain)

Question 5

Why are viruses hard to treat with antibiotics?

Answer 5

Antibiotics kill bacteria by interfering with their metabolic reactions. They target the bacterial enzymes and ribosomes. However, viruses don’t have their own enzymes and ribosomes

Question 6

How is HIV infection controlled?

Answer 6

• Barrier contraception (condoms)
• Antiviral antibiotics