BIOLOGY 2D03 Lecture Notes - Myosin, Central Spindle, Cleavage Furrow

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28 Jan 2013

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Mechanics of Cell Division
Mitosis and Cytokinesis
Interphase DNA is replicated (S phase)
G1 and G2 phases cell growth
M phase nuclear division (mitosis) and cell division (cytokinesis)
M Phase
Chromosome condensation
Then specialized cytoskeletal machines pull the chromosomes apart (mitotic
Finally the cell is split in half (contractile ring)
Chromosome condensation
Sister chromatids bound tightly together by protein complexes called cohesions
after replication in S phase
Cohesions are deposited along the length of each chromatid and are broken only
late in mitosis
At the onset of mitosis chromosomes compacted and become 50x shorter
oCondensins mediate this process use ATP hydrolysis to drive the DNA
compaction rxn
M Phase depends upon the duplication of centrosomes in the preceding interphase
Centrosomes microtubule organizing center (MTOC), nucleate the growth of
oContain a fibrous centrosome matrix containing a pair of centrioles (which
contain about 50 copies of γ-tubulin ring complex)
oThe process of centrosome duplication and separation is called the
centrosome cycle
oAs mitotosis begins, the 2 centrosomes split apart and move to opposite
ends of the nucleus
oEach centrosome (pair of centrioles) nucleates a radial array of
microtubules called an aster, which will become the two poles of the
mitotic spindle
5 stages of mitosis
Prophase sister chromatids condense, and mitotic spindle begins to assemble
outside the nucleus
Prometaphase nuclear envelope breaks down (in mammals)
Metaphase chromosomes are aligned at the equator of the spindle, medway
between the spindle poles. Kinetochore microtubules attach sister chromatids to
opposiute spindle poles
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