5.7 The human immunodeficiency virus

Question 1

Explain the structure of HIV

Answer 1

1. lipid envelope on the outside
2. attachement proteins embedded in lipid envelop
3. capsid (protein layer) that encloses 2 single strings of RNA and some enzymes inside the envelope

Question 2

What does reverse transcriptase (enzyme found within capsid of HIV) do?

Answer 2

It catalyses the production of DNA from RNA- the reverse reaction to that carried out by transcriptase. The presence of reverse transcriptase and consequent ability to make DNA from RNA, means that HIV belongs to a group of viruses called “retroviruses.”

Question 3

How does HIV replicate?

Answer 3

1. Following infection HIV enters the bloodstream and circulates around the body
2. A protein on the HIV readily binds to a protein called CD4. While this protein occurs on a number of different cells, HIV most frequently attaches to helper T cells
3. The protein capsid fuses with the CSM. The RNA and enzymes of this enter the helper T cell
4. The HIV reverse transcriptase converts the virus’s RNA into DNA
5. The newly made DNA is moved into the helper T cell’s nucleus where it is inserted into the cell’s DNA
6. The HIV DNA in the nucleus creates mRNA using the cells enzymes. This mRNA contains the instructions for making new viral proteins and the RNA to go into the new HIV
7. The mRNA passes out of the nucleus through a nuclear pore and uses the cells protein synthesis mechanisms to make HIV particles
8. The HIV particles break away from the helper T cell with a piece of its CSM surrounding them which forms their lipid envelope

Question 4

How does HIV cause symptoms of AIDS?

Answer 4

HIV specifically attacks helper T cells and causes AIDS by killing or interfering with the normal functioning of helper T cells.

Without a sufficient number of helper T cells, the immune system cannot stimulate B cells to produce antibodies or the cytotoxic T cells that kill cells infected by pathogens.

Memory cells may also become infected and destroyed.

As a result, the body is unable to produce and adequate immune response and becomes susceptible to other infections and cancers.

Question 5

Why are antibiotics ineffective against viral diseases like AIDS?

Answer 5

Viruses lack their own metabolic pathways and cell structures. As a result antibiotics are ineffective because there are no metabolic mechanisms or cell structures for them to disrupt.

Viruses also have a protein coat rather than a mue

Question 6

Why are antibiotics ineffective against viral diseases like AIDS?

Answer 6

Viruses lack their own metabolic pathways and cell structures. As a result antibiotics are ineffective because there are no metabolic mechanisms or cell structures for them to disrupt.

Viruses also have a protein coat rather than a murein cell wall and so do not have sites where antibiotics can work.

In any case, when viruses are within an organisms own cells, antibiotics cannot reach them.

Question 7

Define retrovirus

Answer 7

Viruses that characteristically carry their genetic blueprint in the form of ribonucleic acid (RNA)