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Biochemistry Lecture No. 38.docx

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Western University
Biochemistry 2280A
Chris Brandl

Biochemistry Lecture No. 38: Molecular Basis Of Cancer II th Thursday December 6 , 2012 Properties Of Cancer Cells: -Cancer cells divide in the absences of growth factors as they do not respond to signals that normally control cell division (for example, growth factors, hormones); that is, cancer cells do not need these signals to divide. Cancer cells are virtually immortal and do not respond to the normal signals that trigger cell death. Cancer is genetically unstable due to its defective in repair pathways (more point mutations), major chromosome abnormalities. A translocation between chromosomes 9 and 22 is responsible for chronic myelogenous leukemia. Metastatic cancer cells can escape to and proliferate in abnormal places. Avoid replicative cell aging that is programmed by the normal shortening of telomeres that occurs when cells divide. Cancer-Causing Genes: -There are two major types of cancer-causing genes: oncogenes and tumour suppressor genes. An oncogene is a normal gene whose presence in an aberrant form causes cancer (dominant; gain of function). Examples of oncogenes include myc, ras, fos, jun, and abl. A normal gene is referred to as a proto-oncogene (before it has oncogenic properties). The different types of changes that cause a proto- oncogene to become an oncogene include: deletion or point mutations in the coding sequence, gene amplification and chromosome rearrangement (beside a strong promoter or greatly over-expressed fusion products). A tumour suppressor gene is a normal gene whose absence causes cancer (recessive; loss of function). Examples of tumour suppressor genes include p53 (molecule of the year) and Rb. It takes two mutation events for the tumour suppressor gene to lose its function, leading to cancer. Functions Of Cancer-Causing Genes: -Most oncogenes and tumour suppressors code for proteins that act in pathways that respond to signals for cell division or cellular
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