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Lecture 11

BIOB11H3 Lecture Notes - Lecture 11: Tumor Suppressor Gene, G1 Phase, E2F

Biological Sciences
Course Code
Daman Bawa

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Case Study: Defects in the p53 Pathway
Mutations in p53 are present in about 50% of human cancers
Case Study: Retinoblastoma
Retinoblastoma is a rare form of cancer that results due to uncontrolled growth of
retinal cells
This uncontrolled growth occurs due to changes in the retinoblastoma gene (RB)
(tumour suppressor gene)
The incident rate of retinoblastoma is about 1:24,000 births
If detected early, prognosis is good. Radiation treatment or enucleation (removal) of the
eye can be used to treat this.
About 75% of people with retinoblastoma have it in one eye and 25% will have it in both
Steps of retinoblastoma:
1. The RB gene encodes the protein pRB which targets the E2F family of
transcription factorsDuring the G1 phase, pRB is unphosphorylated and
complexed with pRB. This complex acts as a gene repressor for a number of
genes that encode proteins involved in cell cycle progression
2. Activation of CDK results in the phosphorylation of pRB and dissociation from
3. Gene activation/ transcription occurs. This produces a mRNA strand
4. mRNA is translated to proteins that are required for cell cycle progression
5. the G1 phase moves into S phase
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