6.6

Question 1

Describe the structure of HIV

Answer 1

Viral DNA and RNA, encased in a capsid with reverse transcriptase and integrase which is then surrounded by a lipid membrane (made of cell membrane) with glycoprotein120 antigen markers on the outside

Question 2

Explain how HIV infects its host cell

Answer 2

Gp120 binds to CD4 receptor on the outside of a T-Helper cell, allowing it to be accepted into the host cell through endocytosis. The virus then reverse transcripts its RNA into DNA (via reverse transcriptase) which is then integrated (via integrase) into host cell DNA.
The DNA is translated and transcripts as normal, which cause the production of more viruses which leave the cell via budding, taking membrane and cytoplasm with it

Question 3

List the impacts an HIV infection has on the immune system

Answer 3

Less t-helper cells
Less cytokines
Less t-killer and b cells activated, and less antibodies produced - weaker immune response to other threats (eg bacteria)
Immunodeficiency

Question 4

An HIV infection has 3 stages. List these stages and explain why the final stage can result in the death of the individual infected

Answer 4

Acute HIV - intial infection, high in CD4 cells but also high virus count
Chronic HIV - over time, CD4 slowly decreases and virus increases (but virus count is initially less than in acute HIV)
AIDs - severe lack of CD4 cells and hurry high virus count, another pathogen introduction will cause death as the immune system is too weak

Question 5

Explain how the structure of the M. tuberculosis bacteria enables it to evade the immune system

Answer 5

• flagellum - used for movement to escape
• plasmids + pili - contains alleles for antibiotic resistance, which can be passed between bacterium
• cell wall - very thick and waxy, helps deflect chemical immune responses

Question 6

Describe the sequence of events beginning with M. tuberculosis infection and three symptoms that develop

Answer 6

• bacteria get into (upper) lungs, and begin to multiply
• macrophages rush to site of infection and begin engulfing the bacteria
• often all bacteria are engulfed, and the person has latent TB (bacteria are locked in tubercules where they cannot reproduce/cause harm)
• sometimes the bacteria continue to multiply inside the macrophage, evading the immune system until they burst out in greater numbers and the person develops active TB
• weight loss, fever, fatigue, coughing

Question 7

Explain why gas exchange in the lungs is impacted by a M. tuberculosis infection

Answer 7

When the bacteria are locked into tubercules, these areas of the lungs are nonfunctional - reducing gas exchange surface area and therefore reducing gas exchange