Download Cancer and Genome Evolution

Cancer and Genome Evolution
19.3 & 19.5
Lesson 4.7
Genes Associated with Cancer
• Oncogenes – cancer-causing genes in certain
retroviruses
– Mutated versions of proto-oncogenes – genes
that code for proteins that stimulate normal cell
growth and division
– Caused by the following
• Movement of DNA within the genome
• Amplification of a proto-oncogene
• Point mutations
Genes Associated with Cancer
• Tumor-Suppressor Genes – genes whose
normal product INHIBITS cell division
– Proteins produced help prevent uncontrolled cell
growth
Cell Signal Interference
• Ras gene – codes for the Ras protein, which
relays a signal from a growth factor receptor
on a plasma membrane to protein kinases
– At the end of this cycle is a protein that stimulates
the cell cycle
• P53 gene – “guardian angel of the genome”
– codes for DNA repair enzymes, and enzymes to
stop the cell cycle if there is damage
• P. 372
Cancer Development Process
1. Normal epithelial cells lose the tumorsuppressing gene (small, benign growth)
2. Activation of ras oncogene (larger, benign
growth)
3. Loss of p53 gene and additional mutations
(malignant tumor)
Inherited Predisposition to Cancer
• Someone inheriting an oncogene or mutant
allele of a tumor-suppressing gene is one step
closer to accumulating the necessary
mutations of cancer to develop
• 15% of colorectal cancers are inherited
• 5-10% of breast cancer is inherited
How the Genome Evolves
• Evolutionarily, genome would have started
with minimum genes only necessary for
survival and reproduction
• What happened to cause the diverse genome
we have today?
– Duplication (polyploidy – extra sets of
chromosomes)
– Errors in meiosis (crossover between chromatids
that switch genes)
– Exon duplication and shuffling (possible change in
reading frame)