7. HIV and Viruses Flashcards
What is HIV?
Human immunodeficiency virus
It affects human immune system.
Leads to AIDS - acquired immune deficiency syndrome.
What is AIDS?
Immune system deteriorates and fails.
More vulnerable to infections
HIV host cells
It infects& eventually kills helper T cells.
Helper T cells act as host cell for the virus.
Why are T cells so important?
They send chemical signals that activate phagocytes / cytotoxic T-cells and B-Cells.
Without them helper T cells the immune system unable to mount an effective response to infections as eventually helper T cells will reach low level.
The initial infection of HIV
HIV replicated rapidly and infected person may experience severe flu Symptoms.
After, HIV replication drops to lower level = latency period.
During this period (lasts for years) the infected person wont experience any symptoms.
Why does the initial stage of HIV causes flu like symptoms?
The immune system mounts a response to the virus.
Unable to festive all virus so small amount remains in cells and continues to replicate
When do people go from having HIV to AIDs?
When Symptoms of failing immune system start to appear and their helper T cell count drops below a very low level.
How long does it take for HIV to Develop into AIDs?
10 years roughly , without treatment.
Initial stage of AIDS?
Minor infections of mucous membranes
Inside nose/ ears/ genital
Respiratory infections
More susceptible to serious infections like chronic diarrhoea / TB
During late stages of AIDs
Very low number of immune system cells
Serious infections just as toxoplasmosis of the brain - parasite infection
It’s these serious infections that kill the patient not HIV itself
Survival rate with AIDS
Varies a lot
Depends on;
Existing infections / strain of HIV infection / age / healthcare
Antiviral drugs delay time between HIV developing into AIDs
HIV structure
Spherical structure.
Core - genetic material RNA and proteins including reverse transcriptase.
Outer coating of protein called a capsid.
Outer layer called envelope which is made up of the membrane stole from cell membrane of a previous host cells.
Attachment proteins that help HIV attach to host helper T cell
What is significant about the HIV attachment proteins ?
They’re foreign antigens that can be recognised by immune system.
During replication however the virus can change parts of the structure of its attachment proteins - antigenic variation which helps HIV evade destruction of IS
Where does HIV replicate ?
Inside the helper T cells of the host
It doesn’t have the equipment ( enzymes & ribosomes ) to replicate on its own so it uses those of the host cell
Stage 1 of hiv replication
🦠
Attachment protein attached to receptor molecule on the cell membrane of the host helper T cell
Stage 2 of hiv replication
🧬
Capsule is released into helper T cell where it uncoats and released the genetic material (RNA) into cells cytoplasm
Stage 3 of hiv replication
👧 👧
Inside the helper T cell the reverse transcriptase is used to make complementary strand of the DNA from the viral RNA template
Stage 4 of hiv replication
🧬—> 👧
From this replication double stranded DNA is made and inserted into human DNA
Stage 5 of hiv replication
The host cell enzymes are used to make viral proteins from the viral DNA found within human DNA
Stage 6 of hiv replication
Viral proteins are assembled into new viruses which bud from the cell and go infect other cells
When the hiv particles emerges from a cell the cell ruptures and it dies
Why don’t you get given antibiotics for viruses ?
They don’t kill viruses
Don’t get given them for a cold as a cold is rhinovirus
What’s is antibiotics function ?
To kill bacteria
Interferes with metabolic reactions.
They target bacterial enzymes and ribosomes to stop bacterial replication.
Because bacterial enzymes/ ribosomes are different to human ones they don’t damage human cells
Why can’t virus be killed by antibiotics ?
Viruses don’t have their own enzymes / ribosomes they use the ones from the host cells.
So because they use human enzymes/ ribosomes to replicate antibiotics can’t inhibit them they don’t target human processes - or else they would kill healthy human cells.
What medicines/ treatment used for viruses?
Antiviral drugs
Target few virus species enzymes that exist
