Q) Explain how cancer may result due to named factors
Main points | |
Key idea: | Development of cancer when control of the cell cycle is lost |
· Cancer - a disease in which cells undergo uncontrolled cell division · In normal cells, mitotic cell cycle is tightly controlled by diff types of genes : (i) Proto-oncogenes (stimulate cell division), (ii) Tumour suppressor genes (inhibit cell division), (iii) DNA-repair genes (repair damages to DNA) · Cause of cancer : accumulation of mutations in the above genes (i, ii, iii) in a single cell · Result : (i) Abnormal proteins (ii) abnormal levels of proteins affecting cell growth + division | |
Key idea: | Named factor : (1) Chemical mutagen |
· Tar in cigarette smoke, acrylamide in food (e.g. potato chips which are prepared in high temperature above 120oC), etc · Effect : damage or alter DNA of genes | |
Key idea: | Named factor : (2) Ionizing radiation |
· X-rays, ultraviolet (UV) radiation, etc · Effect : penetrate nucleus, form damaging ions inside cells that can cause breaks or mutate DNA, or cause DNA bases to be more reactive | |
Key idea: | Named factor : (3) Viral infection |
· Human papillomavirus (throu sexual contact) - common cause of cervical cancer · Human T-lymphotropic virus (retrovirus) - integrates its genome into human DNA, may insert into and mutate human proto-oncogenes, tumour-suppressor genes or DNA repair genes · Chronic hepatitis B viral infection - a cause of liver cancer ; mode of action - virus directly and repeatedly attack liver cells where chronic inflammation generates DNA-damaging oxidizing agents · Viral DNA with a strong viral promoter inserts near a proto-oncogene, results over-expression of that proto-oncogene, or it contains viral oncogenes whose expression in turn induces uncontrolled cell division | |
Key idea: | Named factor : (4) Genetic factor and gender |
· Some individuals - genetically predisposed to developing certain forms of cancer · E.g. inheritance of one copy of the BRCA1 gene in female increases chance of developing breast cancer by 70% | |
Key idea: | Named factor : (5) Age and immune sys |
· Age and an imperfect immune system increase chance of developing cancer · Reason : these individuals are more susceptible to infection by cancer-causing viruses | |
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) | |
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