2. HIV

Question 1

HIV Host cells

Answer 1

HIV infects and eventually kills helper T- cells.
Helper T-cells send chemical signals to activate phagocytes, cytotoxic T cells and B cells
Insufficient T cells means that the patient is unable to respond to infections effectively
When Helper T cells reach a critically low level the person will develop AIDS

Question 2

Initial Infection

Answer 2

During the initial infection, HIV replicates rapidly
The person may experience severe flu like symptoms
The immune response is unable to destroy all the virus so some remains
The virus continues to replicate but at a lower level
This is known as the latency period and can last for years
The patient will not experience any symptoms

Question 3

When does a person have AIDS?

Answer 3

As the HIV replicates the number of helper T cells drops
A person is described as having AIDS when their Helper T cell counts falls below a certain level.
The length of time between HIV infection and development of AIDS is generally around 10 years
AIDS patients generally develop diseases that wouldn’t trouble a person with a healthy immune system

Question 4

Symptoms of AIDS

Answer 4

Initial symptoms include
Minor infections of mucous membranes and recurring respiratory infections
As disease progresses, the number of helper T cells decreases and person susceptible to more serious infections such as chronic diarrhoea and TB
In the later stages of the disease serious infections such as toxoplasmosis of the brain and candidiasis of the respiratory system occur

Question 5

Structure of HIV

Answer 5

Spherical
The core contains genetic material (RNA) and some proteins e.g. reverse transcriptase
Reverse transcriptase is needed for virus replication
Has an outer protein coat (=Capsid)
It also has an extra outer layer called an envelope made from membrane stolen from a previous host cell.
On the envelope are lots of copies of an attachment protein(= envelope proteins) which help it attach to host helper T cells

Question 6

HIV Replication Facts

Answer 6

HIV can only reproduce inside its’ host cells
It lacks enzymes and ribosomes to reproduce on its own
Attachment proteins are used to attach to receptor proteins on the cell membrane of host cells
During replication HIV can change parts of the structure of these attachment proteins (antigenic variability). This helps the virus evade the immune system

Question 7

HIV Replication Steps

Answer 7

HIV attaches to host cell (Helper T cell, CD4 proteins on surface) using complementary proteins
Capsid released into cell
Uncoats and releases RNA
Reverse transcriptase makes complementary DNA fro RNA
From cDNA double stranded DNA is made
Double stranded DNA inserted into human DNA
Host cell enzymes used to make viral proteins from viral DNA
Viral proteins are assembled into new viruses which bud from the cell and go on to infect other cells
Host cell dies

Question 8

Retrovirus

Answer 8

any of a group of RNA viruses which insert a DNA copy of their genome into the host cell in order to replicate, e.g. HIV