HIV

Question 1

Structure of HIV

Answer 1

-On the outside is a lipid envelope, embedded in which are attachment proteins.
-Inside the envelope is a protein layer (capsid) enclosing two single strands of RNA and some enzymes including reverse transcriptase.

Reverse transcriptase catalyses production of DNA from RNA

Question 2

What is a retrovirus?

Answer 2

A virus that contains the enzyme reverse transcriptase, which causes the reaction that turns viral RNA into a complementary strand of DNA.

Question 3

After infection, what is the first thing HIV does inside the body?

Answer 3

Binds to a CD4 protein on a host cell. Most typically this is a T-helper cell

Question 4

After binding to the CD4 protein, what does HIV do next?

Answer 4

The protein capsid fuses to the host cell’s cell-surface membrane and released its RNA and enzymes into the host cell

Question 5

When inside the cell, what do the RNA and enzymes do?

Answer 5

Turn the viral RNA into a complementary strand of DNA

Question 6

After the DNA is formed, where does it move to?

Answer 6

the host (T-helper) cell’s nucleus. Here it is inserted into the cell’s DNA

Question 7

Outline how HIV replicates using Th cells?

Answer 7

-HIV enters the bloodstream
-the attachment proteins on HIV bind to CD4 protein on Th cell’s cell-surface membrane
-the capsid fuses with the Th cell’s cell membrane
-the viral RNA and reverse transcriptase enter the Th cell
HIV RNA converted into HIV DNA , using reverse transcriptase
-HIV DNA moves into nucleus and binds to Th cell DNA
-HIV mRNA is made, which contains the instructions for the formation of viral proteins (enzymes, attachment proteins, reverse transcriptase, capsid)
-new HIV particle formed
-HIV leaves the Th cell, taking some of it’s cell surface membrane with it (budding)

Question 8

How does HIV cause symptoms of aids

Answer 8

• Infects and kills helper T cells (host cell) as it multiplies rapidly
• T helper cells then can’t stimulate cytotoxic T cells, B cells and phagocytes →
  impaired immune response
• E.g. B plasma cells can’t secrete antibodies for agglutination and destruction
  of pathogens by phagocytosis - Immune system deteriorates
• More susceptible to infections
• Diseases that wouldn’t cause serious problems in healthy immune system are deadly
  (opportunistic infections) e.g. pneumonia

Question 9

Why are antibiotics ineffective against viral diseases eg aids

Answer 9

Antibiotics can’t enter human calls – but viruses exists in its host cell (they are acellular)
- Viruses don’t have own metabolic reactions e.g. ribosomes (use of the host cell’s) which
antibiotics target
- If we did use them… act as a selection pressure + gene mutation = resistant strain of
bacteria via natural selection → reducing effectiveness of antibiotics and waste money

Question 10

Explain why antibiotics are ineffective against viruses

Answer 10

Antibiotics disrupt metabolic mechanisms and cells structures. Viruses do not have these as they rely on host cells to replicate and survive. Viruses are often located inside host cells so antibiotics cannot reach them

Question 11

Antibiotics and bacteria

Answer 11

-inhibit certain enzymes required for synthesis and assembly of the peptide cross-linkages in bacterial cell walls
-weakens walls
-unable to withstand pressure
-water enters naturally by osmosis, the cells urst and bacterium dies