Cells: Cell Recognition & the Immune System - HIV Flashcards
1
Q
What is HIV?
A
- HIV stands for human immunodeficiency virus
- It is a virus that affects the human immune system
- It eventually leads to AIDS
2
Q
What is AIDS?
A
- 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
3
Q
Describe the structure of HIV
A
• 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
4
Q
How does HIV infect cells and replicate?
A
• 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
5
Q
What term is used to describe the dormancy of cells infected with HIV?
A
• 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
6
Q
Describe the symptoms people have during initial infection of HIV and during the period of latency
A
- 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
7
Q
When are people classed as having AIDS?
A
- 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
8
Q
How does HIV cause the symptoms of AIDS?
A
- 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
9
Q
Why are antibiotics ineffective against viruses?
A
- 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
10
Q
Suggest possible treatments for HIV
A
- 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