5.7 HIV

Question 1

Describe the structure of the HIV.

Answer 1

• a lipid envelope on the outside with attachment proteins embedded in it
• surrounding the inside of the envelope is the matrix
• within this is the capsid which encloses 2 single strands of RNA and enzymes such as reverse transcriptase.

Question 2

What is the role of reverse transcriptase?

Answer 2

It catalyses the production of DNA from RNA (reverse of what transcriptase does)
the ability to make DNA from RNA makes it a retrovirus.

Question 3

How does HIV replicate?

Answer 3

• HIV enters the blood stream and circulates
• A protein on HIV binds easily to the CD4 protein which occurs in different cells (mostly helper T cells)
• Protein capsid fuses with cell-surface membrane, RNA and HIV enzymes enter the cell.
• HIV reverse transcriptase converts RNA into DNA
• New DNA is moved into cell’s nucleus and inserted into cell’s DNA
• HIV DNA in nucleus creates mRNA using cell’s enzymes which holds instructions to make new viral proteins and RNA
• mRNA passes out of nucleus through nuclear pore and uses protein synthesis mechanisms to make HIV particles
• HIV particles break away form t helper cell with a piece of cell-surface membrane surrounding them which forms the lipid envelope.

Question 4

How does HIV develop into AIDS?

Answer 4

• HIV causes AIDS by killing or interfering with normal functioning of helper T cells.
• This significantly lowers the number of T cells in the blood.
• without sufficient number the immune system can’t stimulate B cells to produce antibodies or cytotoxic T cells
• The body becomes unable to produce an adequate immune response leaving them susceptible to infections and cancers.

Question 5

How does HIV/AIDS cause death?

Answer 5

• HIV doesn’t kill directly but prevents the immune system from functioning properly
• the weakened immune system means it cannot respond effectively to pathogens.

Question 6

Describe the ELISA test.

Answer 6

1) Apply sample to surface which antigens will attach to.
2) wash surface to remove unattached antigens
3) Add antibody specific to antigen you are trying to detect
4) wash surface to remove excess antibody
5) add second antibody attached to an enzyme which binds with first antibody
6) add colorless substrate of the enzyme. enzyme acts on this to make a colored product.
7) color intensity relates to the amount of antigen present

Question 7

How do antibiotics work?

Answer 7

• the murein cell wall of a bacteria is tough and inelastic so doesn’t burst as a result of osmosis.
• Antibiotics inhibit enzymes required for synthesis and assembly of peptide cross-linkages which make up the cell wall.
• wall is weakened and unable to withstand pressure from osmosis so cell bursts and bacterium dies.

Question 8

Why don’t antibiotics work on viruses?

Answer 8

• viruses rely on host cells for metabolic activities so lack metabolic pathways and structures, therefore antibiotics cannot disrupt metabolic mechanisms or structures
• Viruses also have protein coats rather than murein cells walls so don’t have sites where antibiotics can work
• they are also within body cells so antibiotics can’t access them