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Lecture 28

BIO 201 Lecture 28: The Spindle Assembly Checkpoint; Cancer

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Biological Sciences
BIO 201
Lara Hutson

BIO 201 Dr. Lara Hutson Lecture 28 Notes 4/17/17 The Metaphase-to-Anaphase Transition ● Spindle assembly checkpoint right in the middle of M phase (between Metaphase and Anaphase) ○ Tension ● Metaphase ○ Microtubule depolymerizing inhibitors prevent progression ○ Microtubules attach to chromosomes ● Anaphase ○ Chromosomes segregate toward 2 halves of the cell ● If anything goes wrong during this step, bad things happen Abnormal Segregation of Chromosomes Leads to Chromosomal Nondisjunction ● Karyotype: number and types of chromosomes in a cell ○ Normal karyotype is usually compatible with life ● Abnormal number of chromosomes in cell = cell sees it as DNA damage ○ Cell undergoes apoptosis (programmed cell death) ● Aneuploidy: abnormal number and/or type of chromosomes(s); usually incompatible with life ● Nondisjunction: abnormal chromosome segregation during mitosis or meiosis ○ One pair of sister chromatids fail to disjoin → end up in same daughter cell Kinetochore ● The protein complex that hold sister chromatids together at centromere ● Contains cohesin ○ Protein in kinetochore that hold sister chromatids together until anaphase ○ Degraded by proteases as soon as the spindle is complete and chromosomes are aligned → allows sister chromatids to segregate to 2 halves of the cell How Cell Knows When it is Time to Degrade Cohesin ● At metaphase, MTs pulling from opposite directions might impart tension on kinetochores ● Hypothesis: Tension on the kinetochore causes cohesion degradation ● Experiment: Use a glass needle to pull on a chromosome before 2nd MT attaches ● Result: cohesin degradation and chromosome segregation ○ Suggests tension is what signals cell to degr
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