Bacteria and Viruses

Question 1

Describe structure of a virus

Answer 1

Consist of a nucleic acid (DNA or RNA) enclosed in capsid (protective protein coat), may be covered in lipid layer (envelope) and have attachment proteins helping to attach to suitable host

Question 2

Compare viruses to bacteria

Answer 2

• bacteria = prokaryotic, no nucleus, genetic material stored in circular DNA strand; virus = nucleic acid in protein coat
• bacteria don’t require host to survive; virus entirely dependent
• viruses are much smaller
• bacteria has many organelles (ribosomes, plasmids, flagella, etc) as well as cell membrane and wall, virus has no such structures

Question 3

What type of disease is TB?

Answer 3

Bacterial disease, caused by mycobacterium tuberculosis which infects phagocytes in lungs

Question 4

Describe course of infection for TB

Answer 4

1) symptomless —> infected phagocytes sealed in tubercules in the lungs due to inflammatory response
2) Bacteria dormant in tubercules, not destroyed by immune system due to waxy covering
3) when immune system weakened, bacteria become active and destroy lung tissue leading to symptoms of TB
4) may spread to other parts of the body

Question 5

Describe symptoms of TB

Answer 5

Persistent cough, fever, weight loss, breathing problems, coughing up blood

Question 6

What is AIDS?

Answer 6

Acquired immune deficiency syndrome, starts from HIV and turns to AIDS when immune system very weak

Question 7

What are symptoms of AIDS?

Answer 7

Fever, persistent diarrhoea, weight loss, secondary infections (TB, pneumonia)

Question 8

How does HIV course of infection work?

Answer 8

• HIV (human immunodeficiency virus) attaches to CD4 receptors with gp120 attachment proteins on T helper cells and infects them
• once inside, HIV takes over host DNA and replicates RNA to DNA with cells ribosomes, integrated into host cell DNA
• after virus leaves host, cell bursts due to many replicated DNA strands

Question 9

What adaptations does HIV have to replicate in cells?

Answer 9

~ only contain RNA
~ has enzyme reverse transcriptase, generates DNA from HIV RNA
~ has enzyme integrase, integrates viral DNA with host DNA
~ attachment glycoproteins (gp120) complimentary to CD4 receptors

Question 10

Why does a reduction in T helper cells lead to damage?

Answer 10

• T-killer cells recognise and destroy infected T helpers
• means no activation of macrophages, B cells and T killers
• reduces number of antibodies produced by B cells
• more vulnerable to secondary infections