Thursday, 14 April 2011

Research: A Level Biology

As my animation is being directed towards A level students I felt it necessary to take a trip back to school and make a few notes from the A level textbook (above) concerning HIV (thankfully it has a four page case study). Here are a few things I made a not of:

What are Viruses?

Viruses are the smallest of all the microorganisms and range in size from 0.02 to 0.3um across, about 50 times smaller than the average bacterium.

Viruses are not cells. They are arrangements of genetic material and protein that invade other living cells and take over their biochemistry to make more viruses. It is because of this reproduction, and the fact that they change and evolve in an adaptive way, that they are still classed as living organisms. most scientists working on viruses class them as obligate intracellular parasites, meaning they can exist and reproduce as parasites only in the cells of other living organisms.

Infection by HIV does not lead to AIDs immediately. When people are infected by the virus but have no symptoms, they are HIV positive, as blood tests show the presence of HIV antibodies.

How is HIV Transmitted?

The HIV is very fragile and must be contained in human body fluids - it cannot survive in the air. The source of infection maybe someone who is HIV positive(who may not be aware of their infective status) or someone with active AIDs. The virus can be transmitted from person to person in three main ways:

  • Through sexual contact - the most common way.
  • Through infected blood, by intravenous drug users sharing needles and by the use of infected blood products (where these are not treated).
  • From a mother to her foetus in the early stages of pregnancy, during birth, or through breastfeeding.

How does HIV cause AIDs?

Most of the symptoms of AIDs result from the effect of HIV on the immune system. HIV attaches to the CD4 receptors on the T helper cells and infects them. HIV is a retrovirus and, once inside the T helper cell, it takes over the host DNA and replicates. When the new viruses leave the host T helper cell, it is destroyed. At the same time, host T killer cells recognise and destroy some of the heavily infected T helper cells. The result is a great reduction in the number of T helper cells, which in turn means that the activation of many macrophages and T killer cells simply does not take place. As a result the normal functioning of the T helper cells is lost or reduced, undermining the ability of the immune system to deal with other pathogens. This leaves the individual vulnerable to secondary infections which can kill.

HIV Replication

  • HIV surface protein binds to CD4 cell receptors. Virus envelope fuses with the cell surface membrane.
  • Virus reverse transcriptase copies viral RNA onto viral DNA.
  • Intergrase inserts viral DNA into host DNA.
  • Translation of the virus envelope proteins.
  • Transport of virus envelope protein.
  • Virus envelope proteins are included into the cell membrane.
  • Translation of virus proteins.
  • Virus particle budding becomes wrapped in cell membrane forming the virus envelope.

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