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Two Hit Hypothesis
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Slides 11 CellCycle CellBiology.pdf
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00:01 In the case that we arrive in life, let's say we've got a hereditary form of cancer. 00:07 We have a likelihood of having a cancer. 00:09 We come into life with one mutated copy of that gene. 00:13 We may acquire another mutation or we may not. 00:17 In the case of tumor suppressor genes, we actually need to have two hits. 00:23 Which brings us to the two hit hypothesis. 00:26 So in a tumor suppressor gene, if we came into life with one, we are more likely to acquire another because we already have one. 00:36 Then we would be if we came into life without any copies. 00:40 So we have no copies, and we'd have to acquire two in order for that cancer to develop. The other case is in proto-oncogenes. 00:50 We often only need to have one copy in order for cancer to occur. 00:56 So if we have only one copy, for example, let's say it is a um receptor or a growth factor. For example, if we have a growth factor that has a mutation that binds to the cell receptor and stays bound and won't let go, then we're going to cause a promotion of cell division. 01:21 In the case with the two hit hypothesis, you need two if we have a recessive kind of action. So if we have, for example, if we look at p53. 01:31 p53, if we have one good copy of it, then we have the cell cycle checking. 01:37 We have checking of the DNA to make sure there's no mutations. 01:40 And it takes having two bad copies for there to be no DNA checkpoints. 01:46 So two hit hypothesis means that you have to have two copies of the bad gene. 01:53 And so often a predisposition to cancer means you might have one copy already, and another copy could happen through mutation from teratogens that you experienced during life. So in summary, during this lecture, we have explored the cell cycle. 02:12 You should be able to describe the main events of each of the phases of the cell cycle, as well as diagram the roles of the cyclins and cyclin-dependent kinases in the various checkpoints, and also explain the implications of broken cell cycle controls and how those might lead to cancers. 02:33 I hope you enjoyed this lecture. 02:35 Thank you so much for listening and I look forward to seeing you shortly.
About the Lecture
The lecture Two Hit Hypothesis by Georgina Cornwall, PhD is from the course Cell Cycle and Cell Division.
Included Quiz Questions
What would be a good analogy for a cell with a mutation in both copies of a tumor suppressor gene?
- A car with a brake pedal that does not work
- A car whose gas pedal gets stuck when pushed down
- A car whose gas pedal does not work
- A car that has a gas pedal stuck in an accelerated position
- A car that does not have air conditioning
p53 is a tumor suppressor. What must happen for a tumor suppressor gene to have cancer-causing abilities?
- The gene on both chromosomes must acquire a mutation.
- The gene must undergo one mutation.
- The gene must get replicated several hundred times for it to become cancerous.
- The gene should attach to the promoter region of the oncogenes nearby.
- The gene on one chromosome must undergo three mutations.
Author of lecture Two Hit Hypothesis
Georgina Cornwall, PhD
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