Q) Explain how cancer may result from one named factor
Main points | |
Key idea: | What is cancer |
· Cancer is a disease in which cells undergo uncontrolled cell division | |
Key idea: | Named factor that increase chance of cancer |
· Viral infection – may increase chance of cancer development | |
Key idea: | Human papillomavirus + mode of action |
· May cause cervical cancer · Infection via sexual contact · Involves inactivating protein encoded by p53 tumour suppressor gene · Role of p53 protein : cellular DNA damage activates p53 protein - halts mitotic cell cycle to allow DNA repair; if repair fails, p53 protein induces cell apoptosis · Papillomavirus has an oncogenic gene - codes for a protein that binds to p53, inactivating and/or targeting it for proteolytic degradation | |
Key idea: | Human T-lymphotropic virus + mode of action |
· Retrovirus whole genome randomly integrate into human DNA · May insert into + mutate human proto-oncogenes or tumour-suppressor genes | |
Key idea: | Chronic hepatitis B virus + mode of action |
· A cause of liver cancer · Involves directly + repeatedly attack the liver cells · Result : chronic inflammation generates DNA-damaging oxidizing agents in the liver cell | |
Key idea: | Other modes of action |
· Viral DNA with a strong viral promoter inserts near proto-oncogene · Result : over-expression of proto-oncogene · Virus contains viral oncogenes · Result : expression of oncogenes induces uncontrolled cellular division | |
Key idea: | Multi-step development of cancer |
· Many factors may result in cancer dev but each factor seldom sufficient to cause cancer on its own · Reason : dev of cancer - a multi-step process, requires accumulated mutations of several proto-oncogenes + tumour suppressor genes + DNA repair genes · Ref to various mutations must all occur in single cell | |
Comments: (i) Visualize the answer with the aid of labelled diagrams. (ii) Verbalize the answer + write down the main points w/o referring to the answer (use abbreviations) (iii) Read again within the next 24h & once more within 72h (do not spend more than 10min) (iv) Cancer is a multi-step process which involves the accumulated mutation of several genes (e.g. proto-oncogene, tumour suppressor genes and DNA repair genes) that cause the particular cell to divide continuously, become insensitive to external inhibitory signals, undergo angiogenesis, metastasis and invasion of other normal tissue, and become immune to apoptosis | |
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