Two Hit Hypothesis

by Georgina Cornwall, PhD

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    00:00 We may acquire another mutation or we may not.

    00:04 In the case of tumor suppressor genes, we actually need to have two hits, which brings us to the two hit hypothesis.

    00:13 So in a tumor suppresor gene, if we came into life with one, we are more likely to acquire another because we already have one, then we would be if we came into life without any copies, so we have no copies, and we'd have to acquire two in order for that cancer to develop.

    00:34 The other cases in proto-oncogenes, we often only need to have one copy in order for cancer to occur.

    00:42 So if we have only one copy, for example, let's say it is a growth factor, for example.

    00:54 If we have a growth factor that has a mutation that binds to the cell receptor and stays down and won't let go, then we're going to cause promotion of cell division.

    01:07 In the case for the two hit hypothesis, you need two, if we have a recessive kind of action.

    01:14 So for example if we look at p53. p53 if we have one good copy of it, then we have the cell cycle checking, we have checking of the DNA to make sure there's no mutations.

    01:27 And it takes having two bad copies for there to be no DNA checkpoints.

    01:33 So two hit hypothesis means that you have to have two copies of the bad gene.

    01:40 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.

    01:52 So in summary, during this lecture, we have explored the cell cycle.

    01:58 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.

    02:12 And also explain the implications of broken cell cycle controls and how those might lead to cancers.

    02:20 I hope you enjoyed this lecture. Thank you so much for listening and I'll 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

    1. A car with a brake pedal that does not work.
    2. A car whose gas pedal gets stuck when pushed down.
    3. A car whose gas pedal does not work.
    4. A car that has a gas pedal stuck in an accelerated position.
    5. A car that does not have air conditioning.
    1. The gene on both chromosomes must acquire a mutation.
    2. The gene must undergo one mutation.
    3. The gene must get replicated for several hundred times to show its cancerous
    4. The gene must get attached to the promoter of some oncogenes nearby.
    5. The gene on one chromosome must undergo three hits of mutations.

    Author of lecture Two Hit Hypothesis

     Georgina Cornwall, PhD

    Georgina Cornwall, PhD

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