A well-written FREE biology essay about the causes of disease in humans, marked 25/25 by a Head of Department of Biology. Includes out of spec knowledge and is a great resource for studying.
554 words
“The causes of disease in humans”
25/25 mark essay
5 paragraphs, includes out of spec content
AQA biology
Time taken to write: 23 min 16 sec
One of the causes of disease in humans are pathogens. The HIV virus causes
disease by infecting human cells and inserting its viral RNA into the cell's nucleus,
causing the cell to transcribe and translate the viral RNA to produce viral proteins
which are then assembled to produce new copies of the HIV virus. The large
amounts of the HIV virus cause damage to large numbers of T helper cells via
apoptosis. As a result, the T helper cell count decreases proportionally to the
increasing number of HIV particles in the blood. With a decreased number of T
helper cells, the immune system of the individual becomes a lot more vulnerable to
opportunistic infections. One of the most common opportunistic infections for people
with untreated HIV is bacterial pneumonia, which causes inflammation of a part of the
lungs or the entire lungs.
Other pathogens which can cause disease in humans are bacteria. Bacteria
generally cause disease by releasing toxins into the bloodstream. These toxins are
usually competitive inhibitors of various enzymes. For example, the cholera bacteria
releases toxins which interfere with the adenylate cyclase enzyme. Interference with
this enzyme causes cells in the lining of the gut to open their Ca2+ channels and
release calcium ions into the gut, lowering the water potential inside the gut. As a
result, water flows into the gut to equalise the water potential and less water is
absorbed by the intestinal lining. This causes the host organism to experience
diarrhoea.
Diseases in humans can also be caused by genetics. Mutations in the DNA,
especially deletion mutations occurring early in the genetic code for a particular
protein may cause the production of non-functional proteins. Mutations in proto-
oncogenes and tumour suppressor genes may increase the risk of developing a
tumour. Healthy proto-oncogenes send signals to the cell to start mitotic division,
however, mutations in these genes may cause the cell to receive abnormally large
numbers of mitosis triggers, causing it to divide uncontrollably. Healthy tumour
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