HIV and Viruses Flashcards
What is HIV?
HIV (Human Immunodeficiency Virus) is a virus that affects the immune system
What does HIV eventually lead to?
HIV eventually leads to acquire immune deficiency syndrome (AIDS)
What is AIDS?
AIDS (acquired immune deficiency syndrome) is a condition where the immune system deteriorates and eventually fails. This makes someone with AIDS venerable to other infections
What cells does HIV infect?
HIV infects (and kills) T-helper cells, which act as host cells. T-helper cells are important because they send chemical signals that activate phagocytes, cytotoxic T-cells and B-cells. Without enough T-helper cells the immune system is unable to mount an effective response to infections
When do people with HIV develop AIDS?
People with HIV are classed as having AIDS when symptoms of their failing immune system start to appear or their helper T-cell count drops below a certain level
What is the structure of HIV?
HIV has a spherical structure:
- A core that contains genetic material (RNA) and some proteins (including the enzyme reverse transcriptase, which is needed for virus replication)
- An outer coating of protein called a capsid
- An extra outer layer called an envelope. This is made of membrane stolen from the cell membrane of a previous host cell
- Sticking out from the envelope are loads of copies of an attachment protein that help HIV attach to the host helper T-cell
Where does HIV replicate?
HIV can only reproduce inside helper T-cells. It uses the organelle inside the helper T-cell to replicate itself
How does HIV replicate?
- The attachment protein attaches to a receptor molecule on the cell membrane of the host helper T-cell
- The capsid is released into the cell, where it uncoats and releases the genetic material (RNA) into the cell’s cytoplasm
- Inside the cell, reverse transcriptase is used to make a complimentary strand of DNA from the viral RNA template
- From this, double-stranded DNA is made and inserted into the human DNA
- Host cell enzymes are used to make viral proteins from the viral DNA found within the human DNA
- The viral proteins are assembled into new viruses, which bud from the cell and go on to infect other cells
What is the length of time between infection with HIV and the development of AIDS?
The length of time between infection with HIV and the development of AIDS varies between individuals, but without treatment it’s usually around 10 years
How does AIDS progress?
The initial symptoms of AIDS include minor infections of mucous membranes, and recurring respiratory infections. As AIDS progresses the number of immune system cells decreases further. Patients become susceptible to more serious infections including chronic diarrhoea, severe bacterial infections and tuberculosis. During the late stages of AIDS patients have very low numbers of immune system cells and develop a range of serious infections such as toxoplasmosis of the brain and candidiasis of the respiratory system. It’s these serious infections that kill AIDS patients, not HIV
What factors affect the progression of HIV to AIDS and survival time?
Existing infections, the strain of HIV they’re infected with, age and access to healthcare
How do antibiotics kill bacteria?
Antibiotics kill bacteria by interfering with their metabolic reactions. They target the bacterial enzymes and ribosomes used in these reactions
Why don’t antibiotics kill human cells?
Bacterial enzymes and ribosomes are different from human enzymes and ribosomes. Antibiotics are designed to only target the bacterial ones so they don’t damage human cells
Why can’t antibiotics target viruses?
Viruses don’t have their own enzymes and ribosomes - they use the ones in the host cell. Because human viruses use human enzymes and ribosomes to replicate, antibiotics can’t inhibit them because they don’t target human processes
What are antiviral drugs designed to target?
Most antiviral drugs are designed to target the few virus-specific enzymes that exist
