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L312/Spring 2007 Lecture 21 Drummond April 5

L312/Spring 2007 Lecture 21 Drummond April 5. For today: Finish Ch. 19 Mitosis and cytokinesis (cytokinesis today) +Ch.5 (181-91) Class evaluation at end of class today if time permits Last time: Mitosis revisited, with emphasis on molecular details

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L312/Spring 2007 Lecture 21 Drummond April 5

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  1. L312/Spring 2007 Lecture 21 Drummond April 5 For today: Finish Ch. 19 Mitosis and cytokinesis (cytokinesis today) +Ch.5 (181-91) Class evaluation at end of class today if time permits Last time: Mitosis revisited, with emphasis on molecular details Reconsider roles of microtubules and membranes in mitosis Revisit the sequence of events Distinguished 4 classes of microtubules interphase interpolar aster kinetochore Today: Reconsider ‘mitotic’ chromosomes and DNA compaction during mitosis Critically compare features of microtubules and MAPs in mitosis XKCM-1 and XMAP-215 (X = xenopus, a favored frog) Focus on anaphase: entry and events The steps in mammalian cytokinesis The role of actin and myosin

  2. Contrast the role of microtubules in interphase and mitosis Pay close attention to each of the structures Key questions: what happens to the micro- tubules? Why (how) do they form new structures to support mitosis? (MAPs!!!!) What happens to the DNA? (Compaction!!!)

  3. The nucleus (and DNA) is highly organized

  4. Chromatin condenses during interphase Why are DNA strands held together after synthesis? (2 key reasons) what is the contribution of the histone code here?

  5. Electron micrograph of compacted mitotic chromosomes (DNA + protein!) Where are the cohesins? Condensins?

  6. What are mitotic chromosomes, and how are they compacted? Histone code mediates accessibility of free DNA Condensins, among others, mediate compaction

  7. Chromosomes separate at anaphase Specific proteases degrade cohesins APC (anaphase promoting complex) is cell cycle (cyclin) regulated and promotes progression--how?

  8. The role of APC in cohesin degradation (one of many roles) (rate?) Now revisit microtubules

  9. A comparison of interphase and mitotic microtubules What is the Mitotic spindle? Be able to identify and contrast differences in stability, length, function (could changes in GTP concentration account for the differences?) (MAPs!!! How can you define the roles of MAPs?)

  10. Studying the effects of proteins in Xenopus egg extracts XKCM1 depleted From extract by Antibody Normal cell XKCM1* = xenopus kinesin central motor protein 1 (based on sequence, not exact functional parallel) What is a catastrophin? *Claire Walczak did this!

  11. Many MAPs (microtubule associated proteins) stabilize microtubules Normal Antibody depleted

  12. Anaphase: what moves and why? Movie--watch for details

  13. Which organelles or structures break down and which remain intact? Mitochondria Lysosomes ER Golgi Nuclear envelope and lamina

  14. Actin and myosin are central to cell resolution into two cells What are possible roles for the interpolar microtubules at this late stage? Initiated in anaphase

  15. What happens to the integrins during cytokinesis?

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