Topic Molecular Biology of Cancer Essay - Main Points!

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)

Topic Molecular Biology of Cancer Essay - Main Points!

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