Cells: Cell Recognition & the Immune System - HIV

Question 1

What is HIV?

Answer 1

• HIV stands for human immunodeficiency virus
• It is a virus that affects the human immune system
• It eventually leads to AIDS

Question 2

What is AIDS?

Answer 2

• AIDS stands for acquired immune deficiency syndrome
• AIDS is a condition where the immune system deteriorates and eventually fails
• Makes people more vunerable to other infections

Question 3

Describe the structure of HIV

Answer 3

• Core

• Contains genetic material (RNA)
• Contains some molecules (e.g enzyme reverse transcriptase - needed for virus replication)

• Outer layers

• Has an outer coating of protein called a capsid
• Has an extra outer layer called the lipid envelope -made of membrane taken from material surrounding the host cell
• Sticking out the envelope are copies of attachment proteins that help HIV attach to the host helper T-cell

Question 4

How does HIV infect cells and replicate?

Answer 4

• Invasion of cells

• HIV attaches to the helper T cells
• The T cells have receptor molecules that bind to the attachment proteins of HIV
• The HIV enters and releases RNA into the cell

• Transcription of RNA

• The reverse transcriptase transcribes the viral RNA into DNA
• The viral DNA made is called a provirus
• The viral DNA (provirus) is spliced into the host cell DNA
• The host cell is now ready to make copies of the virus
• Cells experience period of latency

• Replication

• Host cell enzymes make viral proteins from viral DNA
• These assemble into new viruses, which burst out of the cell, destroying it

• Further infection

• Viruses infect more T cells and destroy them
• The immune system is more and more compromised

Question 5

What term is used to describe the dormancy of cells infected with HIV?

Answer 5

• Period of latency

• HIV replication drops and cells become dormant
• The viral DNA awaits a chemical signal to prompt the host cell to produce new virus

Question 6

Describe the symptoms people have during initial infection of HIV and during the period of latency

Answer 6

• During the initial infection period, the infected person may experience severe flu-like symptoms
• After this, the latency period begins and the infected person won’t experience any symptoms
• This is because HIV replication drops and cells become dormant
• The latency period can last years

Question 7

When are people classed as having AIDS?

Answer 7

• People with HIV are classed as having AIDS when:
• Symptoms of their failing immune system start to appear
• Or when their T cell count drops below a certain level

Question 8

How does HIV cause the symptoms of AIDS?

Answer 8

• HIV kills T cells which are required for the specific immune response
• Without these, there is no response to pathogens and no immunological memory
• The body cannot fight infection with pathogens
• As AIDS progresses, the number of immune system cells decreases further and patients become susceptible to more serious infections
• Death is not directly from HIV, but is from secondary infections – most commonly TB and pneumonia

Question 9

Why are antibiotics ineffective against viruses?

Answer 9

• Antibiotics kill bacteria, not viruses
• This is because many antibiotics work by preventing bacteria from making cells walls
• Without this the bacterial cell cannot control the entry and exit of water and will therefore burst
• Viruses don’t have a cell wall and are reproduced within a host cell so they are unaffected by antibiotics

Question 10

Suggest possible treatments for HIV

Answer 10

• Use antibodies that target the antigens of HIV before it enters T cells
• Use enzyme inhibitors to block the reverse transcriptase, therefore preventing reverse transcription and viral replication