5 HIV

Structure of HIV

Has a lipid envelope on the outside
Peg-like attachment proteins embedded in the envelope
Inside the envelope is a capsid - protein layer
Inside the capsid is two single strands of RNA
Along with the RNA are some enzymes
One enzyme is reverse transcriptase. This catalyses the production of DNA from RNA. Due to this, HIV belongs to a group of viruses called retroviruses

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HIV enters the bloodstream and circulates around the body
A protein called CD4 is on many different human cells but HIV most frequently attaches to T helper cells
The capsid fuses with the cell-surface membrane
The RNA and enzymes of HIV enter the T helper cell
The reverse transcriptase converts HIV RNA into DNA
Newly-made DNA is inserted into the T cell's DNA
HIV DNA creates mRNA which contains instructions on how to make more of the enzymes needed for HIV production
Protein synthesis produces all of the proteins which make new HIV particles
HIV particles break away from the T cell using the T cell's cell-surface membrane as a lipid envelope

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HIV specifically attacks T helper cells
HIV causes AIDS by killing or interfering with the normal function of T helper cells
An uninfected person has between 800 and 1200 helper T cells per mm cubed of blood
An infected person has less than 200 T cells per mm cubed of blood
T helper cells are important for cell-mediated immunity
Without enough T helper cells, the immune system cannot stimulate B cells to produce enough antibodies to deal with the infection
Memory cells can also become infected and destroyed so the secondary immune response is also impacted by AIDS
Many AIDS sufferers develop infections in the lungs, intestines, brain and eyes as well as experiencing weight loss and diarrhoea
It is the secondary diseases that ultimately lead to death

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ELISA - enzyme-linked immunosorbent assay
Uses proteins to detect disease and also how prevalent the disease is within a sample
Apply the sample to a surface to which all of the antigens will attach
Wash the surface several times to remove any unattached antigens
Add the antibody that is specific to the antigen that we are trying to detect and leave them to bind together
Wash the surface to remove excess antibody
Add a second antibody that binds to the first antibody
This second antibody has an enzyme attached to it
Add the colourless substrate that is complementary to the enzyme to the slide
When the enzyme controlled reaction happens a colour is produced showing the presence of the disease and the amount of colour produced shows the intensity of the disease
Works for HIV, tuberculosis and hepatitis and it is especially useful when needing to find the quantity of the disease instead of just a positive or negative detection of a pathogen

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Antibiotics prevent bacteria from producing normal cell walls
In cells, Water constantly moves in by osmosis which doesn't cause the cell to burst because of the wall made of murein in bacteria which is tough and not easily stretched
Antibiotics like penicillin inhibit enzymes that are used to produce murein by stopping the creation of the peptide bonds
This weakens the walls making them unable to withstand the pressure caused by water entering the cells by osmosis
This causes the cell to burst

Viruses rely on host cells to carry out their metabolic pathways and produce cell structures
Antibiotics are therefore ineffective as there aren't any metabolic processes to stop or disrupt
When antibiotics are in cells the antibiotics cannot reach them

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