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CELL DIVISION. Stages of mitosis (animal cell) prophase: - chromosomes condense (replicated in S phase) - centrosomes separate (duplicated in S phase)

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Presentation on theme: "CELL DIVISION. Stages of mitosis (animal cell) prophase: - chromosomes condense (replicated in S phase) - centrosomes separate (duplicated in S phase)"— Presentation transcript:

1 CELL DIVISION

2 Stages of mitosis (animal cell) prophase: - chromosomes condense (replicated in S phase) - centrosomes separate (duplicated in S phase) prometaphase: - nuclear envelope breaks down - MTs contact chromosomes, spindle forms

3 metaphase: - chromosomes align at spindle equator (metaphase plate) anaphase: - sister chromatids separate - chromosomes move to poles - poles move apart telophase: - nuclear envelope reforms - chromosomes decondense - interphase array of MTs reforms cytokinesis: - contractile ring pinches cell in two

4 Centrosome cycle (animal cell): - centrosome (centriole) duplication begins at the start of S phase - remains as one complex until M phase In early embryonic cells, the centrosome cycle can operate without a nucleus - egg cell extracts

5 Mediators of mitotic chromosome structure: - cohesins: deposited along the length of sister chromatids as the DNA is replicated - hold sisters together - condensins: coil DNA - mediate chromosome condensation

6 Structure of a spindle: 3 classes of MTs (polar MTs) How does a spindle form, and how does it work to separate chromosomes?

7 Prophase: changes in MT dynamics - more MTs nucleated from centrosome - shorter, more dynamic MTs Quantifying MT dynamics: - inject fluorescent tubulin - bleach with laser - measure recovery (newly formed MTs) - t1/2 = time to 50% recovery

8 MT dynamics: regulated by MAPs vs. catastrophins higher catastrophe rates = shorter MTs centrosomes incubated in Xenopus egg extracts

9 Spindle formation in vitro: mitotic extracts + DNA + centrosomes - abnormal spindles form when ratio of MAPs:catastrophins is perturbed no MAP (MTs are too short)

10 Centrosome separation in prophase is driven by plus-end motors (KLPs) - balanced by minus-end motors

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12 Yeast mutants: identification and characterization of spindle motors (-) (+)

13 Prometaphase: kinetochores capture MTs (mechanism of attachment??)

14 Forces that drive chromosomes to metaphase plate: - kinetochores pull chromosomes to poles: (-)end directed motors? - astral ejection force: (+)end directed motors on chromosome arms

15 Metaphase: - chromosomes continue to oscillate at metaphase plate (vertebrate cells) - MTs undergo poleward flux (function?)

16 - poleward flux of metaphase MTs can be measured with caged fluorescein

17 Dynamics of individual MTs can be measured with fluorescence speckle microscopy: - poleward flux of metaphase MTs occurs in kinetochore and overlap MTs but not in astral MTs

18 Anaphase A: - kinetochore MTs shorten - chromosomes move to poles Fluorescent tubulin injections show locations of MT growth, depolymerization

19 Two models for kinetochore movement along MTs:

20 Anaphase B: - poles separate - overlap MTs lengthen

21 Model for motor protein activity in anaphase B

22 Bipolar spindles can assemble without centrosomes or chromosomes

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24 Cytokinesis (animal cell)

25 What determines the position of the cleavage furrow? - signal from asters to cortex - signal from central spindle - chosen before mitosis (position of spindle from previous mitosis)

26 Contractile ring of actin and myosin: red = actin, green = myosin II

27 Cytokinesis in plants

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