BIOL1004 Lecture Notes - Lecture 3: Gene Duplication, Oncogene, Cell Cycle
BIOL1004: Topic 4 – Cancer
Lecture 3 – Oncogenes and the Cell Cycle
• Oncogene = altered or over-expressed versions of normal genes which regulate growth
• Normal gene = proto-oncogene
• Genes that cause cancer
• Ways to change proto-oncogenes to oncogenes
o Deletion or point mutation in coding sequence
• RAS
o Regulatory mutation
• Mutation in promotor
• Causes them to be expressed more or less (in this case, more)
o Gene amplification
• Instead of 1 gene, you have 5
o Chromosome rearrangement
• Hyperactive fusion protein (mic)
• Oncogene collaboration
o Genetically alter mice
o Overexposed copy of mic put in front of the promotor of mammary epithelium (only
expressed here)
o Point mutation if RAS gene, cancer will be seen in 50% of mice after 200 days (see graph)
o RAS + mic means that cancer occurs faster and at a very high frequency
The cell cycle
• Process by which cells divide:
o G1 (gap 1) - checking DNA
o S (synthesis of DNA)
o G2 (gap 2)
o M (mitosis)
• Prophase
• Metaphase
• Anaphase
• Telophase
o G0 = cell not in cell cycle
• Cancerous cells go through the cell cycle at normal speed
• Greater proportion of the cells the cell cycle
• Few cells die
• Normal tissue: cell growth = cell death
• Regulated by cyclins and cyclin-dependent kinases (CDK)
• Cyclin is made and the quickly broken down
• CDK: enzyme that phosphorylases, adds a phosphate
o Is inactive when unbound to cyclin
o Cyclin is tightly controlled, hence controlling the activity of CDK
• Phosphatases remove phosphate
o RAS is a phosphatases
• Two major checkpoints in the cell cycle
o Checkpoint 1 between G1 and S, to check all the DNA is fine
o Second is between G2 and M, to ensure all relocated DNA (both copies) care ok
• G2-Mitosis
o Checks that DNA replication is complete, no breaks in DNA
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