AS/A-level Biology - Cancer

When it comes to AS/A-level Biology, do you remember what triggers cancer?

• Cancer occurs when the rate of cell multiplication is faster than the rate of cell death.
• This causes the growth of a tumour (a mass of abnormally growing and uncontrollable cells) which is often in tissues with a high rate of mitosis, e.g. the lungs.
• Cancers are caused by damaged DNA.
• Cancer cells do not respond to the mechanisms that control the cell cycle.
• Two types of gene have a role in control of the cell cycle and play a part in triggering cancer:

(1) Oncogenes code for proteins that stimulate the transition from one stage in the cell cycle to the next, therefore mutations in this gene can lead to the cell cycle being continually active, therefore causing excessive cell division.
 

(2) Tumour suppressor genes produce suppressor proteins that stop the cycle, therefore mutations inactivating these genes mean there is no break in the cycle

• E.g. the p53 protein stops the cell cycle by inhibiting the enzymes at the G1/S transition, preventing the cell from copying its DNA. 

• Many gene defects (DNA damage in the embryo) have been identified that predispose people to cancers such as bowel, ovarian, prostate, retinal and some leukaemia’s.
• E.g. mutations in the BCRA1 gene predispose a person to breast cancer - the functioning gene produces a protein used to repair DNA.

(i) Chemical                                                                                                                                   

• A diet with plenty of fruit and vegetables provides antioxidants which destroy radicals which could potentially damage DNA.
• Smoking increases the likelihood of lung cancer through the action of carcinogens in tar - tar lodges in the bronchi and causes damage to the DNA in the surrounding epithelial cells.

(ii) Viral

• Liver cancer can follow hepatitis.
• Cervical cancer can follow infection by the papilloma virus.

(iii) Physical

• UV light physically damages DNA in skin cells, sometimes a mole which has been affected by UV light may start to grow bigger, and develop into a tumour.
• Cancer cells sometimes spread to other parts of the body, carried in the blood and lymphatic systems.

That's the end of the topic!

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