HIV

Question 1

What is the structure of the HIV virus?

Answer 1

• smaller than bacteria
• acellular
• can only replicate inside a living cell
• genetic material contained is wither RNA or DNA within a core
• core surrounded by capsid (protein coat)

Question 2

Further structure of HIV virus

Answer 2

• spherical
• envelope of lipids embedded with peg like attachment proteins
• inside the envelope is a cone shaped capsid containing 2 strands of RNA and enzymes- reverse transcriptase
• retrovirus (RNA)

Question 3

What does reverse transcriptase do?

Answer 3

• catalyses production of DNA from RNA
• reverse of transcriptase

Question 4

How does HIV enter T-helper cells?

Answer 4

• HIV enters the bloodstream
• protein in HIV attaches to protein on the T-helper cell
• virus fuses with T cell - viral RNA and enzymes enter the cell
• reverse transcriptase converts HIV RNA to DNA
• DNA copy is inserted into the T helper cell’s DNA
• when cell division occurs viral DNA is copied too (cell remains normal at this point)

Question 5

How does a person become HIV positive?

Answer 5

• person is said to be HIV positive at this stage as they are infected with the virus and have antibodies against it in their bloodstream
• at some point (can be years later), virus DNA becomes active
• takes over the cell and causes many more HIV viruses to be made

Question 6

How are new HIV molecules created?

Answer 6

• HIV DNA creates new mRNA using T helper cell enzymes
• this mRNA contains instructions for making new viral proteins and is the RNA that will go into new HIV molecules
• viral mRNA passes out of the nucleus and uses protein synthesis mechanisms to make new HIV particles
• these HIV particles break away from the T-helper cell, using some of the cell-surface membrane as its lipid envelope
• millions of HIV particles are made this way, causing the cell to die and the release of new infective HIV which infect more T helper cells

Question 7

How does infection from HIV cause symptoms of AIDs?

Answer 7

• T helper cells are killed as the virus leaves but may also be killed by other T cells in the cell mediated response to cells infected with a virus
• T cell number is drastically reduced
• this means B cells are not stimulated to release antibodies and killer T cells not stimulated (memory cells maybe infected or destroyed)
• immune response severely impaired = susceptible to infections and cancers
• not HIV that kills people but the infections by other pathogens that the immune system cannot defeat due to lack of T cells

Question 8

What are the symptoms of AIDs?

Answer 8

• meningitis, tumours, pneumonia, gastrointestinitis
• kaposi sarcoma - AIDs defining illness

Question 9

What does HIV stand for?

Answer 9

• human immunodeficiency virus