133260
Description
Mind Map by harry_bygraves, updated more than 1 year ago
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Created by harry_bygraves
almost 11 years ago
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Cell division; stimulation
and suppression
- Healthy body tissue cells divide by mitosis so that growth and repair can take
place. The regulatory mechanism involves specific genes that carefully coontrol
the process. In particular, normal cellular genes, called proto-oncogenes, code
for proteins that stimulate normal cell growth and division. When growth or repair
is completed, other genes called tumour supressor genes inhibit cell divsion
- The proteins encoded by tumour suppressor genes may; repair
damaged DNA before it can be replicated, control cell adhesion and
ensure that cells are anchored in their proper place, inhibit cell division
- In a healthy cell, the activites of these proto-oncogenes
and tumour supressor genes are in balance. Problems
arise when the genes mature or other control mechanisms
break down so that cells divide uncontrollably
- Proto-oncogenes can mutate into cancer-causing genes called oncogenes. The presence of oncogenes
leads to either; an increase in the amount of proteins that stimulate cell growth and division. OR.. an
increase in the activity of each growth-stimulating protein molecule- the mutation may lead to an altered
protein that is hyperactive or that resists being broken down when it is no longer needed
- Either of these effects can lead to abnormal stimulation of the cell
cycle and result in the development of a malignant tumour.
- Any mutation that decreases the activity of tumour supressor genes can also lead to a malignacy. Such a mutation
mat allow the rate of cell division to increase through the lack of suppression, or it may lead to cells losing thrit
normal anchorage and invading other parts of the body where they might develop into a malignant tumour
- The mutation of either a proto-oncogene into an oncogene or a
tumour suppressor gene into one that no longer suppresses cell
division may be spontaneous, or it may be triggered by specific
cancer-causing agents called carcinogens. Spontaneous
muations may occur as random events during DNA replication.
They may lead to a point mutation that alters the nucleotide
base sequence in the gene and the protein encoded by it
- Factors that trigger muations include; chemical carcingoens, such as those
in tobacco smoke; physical agents, such as X-rays; and certian viruses.
- Retroviruses capsules contain RNA and reverse
transcriptase,an enzyme that transcribes DNA from the
template formed by the RNA. The resulting viral DNA, which
may contain an oncogene, is incorporated into a hosts cell as
a provirus. The hosts RNA polymerase transcribes the virla
DNA into RNA molecules. This RNA may finction as mRNA to
make viral proteins, or it may form the RNA contained within
the capsule of new viruses particles released from the cells
- Most mutated cells are either destroyed by the body's immune system or die, causing no harm.
However, a single mutated cell divide to form a clone of idnetical cells. Eventually a mass of
abnormal cells called a tumour is formed. Benign tumours such as warts do not spread form their
point of origin. Tumours that can spread through the body are called maligant tumours
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