Cell Cycle And Cancer Flashcards
What is a proto-oncogene?
A normal version of a gene who normal gene products play a role in controlling cell division.
What roles could be played by the normal gene products of proto-oncogenes?
External signals for growth e.g. hormones and peptide growth factors
Cell surface receptors such as EDFR and HER2
Intracellular molecules e.g. signal transducers, cyclins, transcription factors
How can proto-oncogenes be converted to their oncogenic forms which will result in uncontrolled cell division and tumour formation?
By certain activating mutations allowing cells to bypass the need for extracellular growth signals
Proto-oncogenes are dominant acting. What does this mean?
Only one copy of the gene needs to be affected by an activating mutation for tumour formation to occur
In what ways can oncogenes cause tumour formation?
By coding for a hyperactive version of protein products
By coding for a normal proteins but in abnormal quantities/at the wrong time/in the wrong cell type
How can chromosomal rearrangement lead to gene amplification that generates a normal protein but in abnormal circumstances leading to cancer?
By placing the gene downstream of a strong promoter region
How do telomeres prevent the cell from dividing indefinitely?
Each time a cell divides the telomere shortens.
What is the normal role of a telomere?
To stop end to end fusion of chromosomes
How is the enzyme telomerase involved in tumour formation?
This enzyme (which adds on new parts to prevent telomere shortening) is normally inactive but can become active in cancerous cells meaning that the telomere never shortens and the cell becomes immortal.
What is the normal role of tumour suppressor genes in the cell?
To apply a brake on cell proliferation
Tumour suppressor genes are dominant acting. T/F?
False - they usually require mutations in both genes to cause tumour formation
The protein retinoblastoma is an example of a product of a tumour suppressor gene. What is its role and how is it implemented in cancer?
Rb binds to and prevents the action of several transcription factors. Phosphorylation causes it to release these factors and for proliferation to occur. When it is damaged it can lead to the over expression of gene products which promote proliferation.
How is the need for extracellular signals to stimulate cell proliferation overcome by cancer cells?
By activation of proto-oncogenes
How are cellular mechanisms that impose constraints on proliferation overcome by cancer cells?
Loss of tumour suppressor genes
Constitutive expression of telomerase
How are cellular mechanisms that prevent persistence of damaged cells overcome by cancer cells?
By loss of tumour suppressor genes
