The Human Immunodeficiency Virus (HIV) Flashcards
What is the structure of the human immunodeficiency virus?
Outside is a lipid envelope, with attachment proteins embedded in it. Inside the envelope is a protein layer called the capsid that encloses two single strands of RNA and some enzymes.
What is one of the enzymes in the capsid called and what is its function?
Reverse transcriptase, catalyses the production of DNA from RNA. The ability to make DNA from RNA means HIV belongs to a group of viruses known as retroviruses.
How does HIV replicate?
- HIV enters bloodstream and circulates the body.
- Protein on HIV binds to a protein called CD4, HIV most frequently attaches to helper T cells.
- Protein capsid fuses with cell-surface membrane. RNA and enzymes of HIV enter helper T cell.
- HIV reverse transcriptase converts virus’s RNA into DNA.
- DNA moves into helper T cell’s nucleus where it is inserted into the cell’s DNA.
- HIV DNA in nucleus creates mRNA using cells enzymes. mRNA contains instructions for making new viral proteins and RNA to go into new HIV.
- mRNA passes out of nucleus through a nuclear pore and uses cell’s protein synthesis mechanisms to make HIV particles.
- HIV particles break away from helper T cell, with a piece of its cell-surface membrane surrounding them forming their lipid envelope.
How does HIV cause AIDS?
HIV specifically attacks T helper cells. HIV causes AIDS by killing or interfering with normal function of helper T cells. Without a sufficient number of helper T cells, the immune system cannot stimulate B cells to produce antibodies or cytotoxic T cells to kill infected cells.
What happens as a result of AIDS?
Body is unable to produce immune response and becomes susceptible to other infections and cancers. It is the secondary diseases of AIDS that results in death
What is the ELISA test and what is it used for?
ELIZA stands for enzyme linked immunosorbant assay. It uses antibodies to detect the presence of a protein and also the quantity. It is extremely sensitive and so can detect very small amounts of the molecule. Useful in drug and allergen tests.
How is the ELISA test carried out?
- Apply sample to a surface to which all the antigens in the sample will attach.
- Wash the surface several times to remove unattached antigens.
- Add specific antibody to antigens we are trying to detect and leave to bind together.
- Wash surface to remove excess antibody.
- Add a second antibody to bind with first antibody, this has an enzyme attached to it.
- Add colourless substrate of enzyme. Enzyme acts on substrate causing it to change into a coloured product.
- Amount of antigen present is relative to intensity of developed colour.
How do antibiotics work to kill bacteria?
Antibiotics, such as penicillin, inhibit certain enzymes required for synthesis and assembly of peptide linkage in bacterial cell walls. This weakens the walls, making them unable to withstand pressure. As water enters bacterium by osmosis, the cell bursts and bacterium dies.
Why are antibiotics ineffective against viruses?
Antibiotics don’t work as viruses don’t have their own metabolic pathways and cell structures, so can’t disrupt them. Viruses also have a protein coat rather than a murein cell wall and so do not have sites where antibiotics can work. When viruses are inside an organism’s own cells, antibiotics cannot reach them.
