L312Spring 2007Lecture 21Drummond April 5

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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
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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!!!)
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The nucleus (and DNA) is highly organized
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Chromatin condenses during interphase
Why are DNA strands held together after
synthesis? (2 key reasons) what is the
contribution of the histone code here?
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Electron micrograph of compacted mitotic
chromosomes (DNA protein!)
Where are the cohesins? Condensins?
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What are mitotic chromosomes, and how are they
compacted?
Histone code mediates accessibility of free DNA
Condensins, among others, mediate compaction
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Chromosomes separate at anaphase
Specific proteases degrade cohesins APC (anaphase
promoting complex) is cell cycle (cyclin)
regulated and promotes progression--how?
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The role of APC in cohesin degradation (one of
many roles)
(rate?)
Now revisit microtubules
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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?)
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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!
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Many MAPs (microtubule associated proteins)
stabilize microtubules
Normal Antibody depleted
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Anaphase what moves and why?
Movie--watch for details
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Which organelles or structures break down and
which remain intact?
Mitochondria Lysosomes ER Golgi Nuclear envelope
and lamina
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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
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What happens to the integrins during cytokinesis?