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Lecture 21

BIOL 3113 Lecture Notes - Lecture 21: Cell Division, Sister Chromatids, Cytokinesis

Course Code
BIOL 3113
Barbara S

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21 Cell Division
Cell Cycle
The cell cycle is the series of events that occurs in the life of a eucaryotic cell from one
cell division to the next
The eucaryotic cell cycle is divided into four phases:
*M phase
mitosis - chromosome division
cytokinesis - cytoplasmic division
*G1 phase
period of normal cell function
*S phase
DNA synthesis
*G2 phase
preparation for mitosis
G1 + S + G2 = Interphase
Division of a eucaryotic cell (M phase) two daughter cells with the same chromosome
complement as the parent cell
Two phases:
*Chromosome (nuclear) division - mitosis
*Cytoplasmic division cytokinesis
Three key features of the M phase of the cell cycle:
*Chromosome condensation - allows the chromosomes (DNA + proteins) to be separated
without becoming tangled
condensins - help to carry out chromosome condensation
cohesins - held two sister chromatids together
*Mitotic spindle - provides the mechanism to separate the daughter chromosomes,
composed of microtubules
*Contractile ring (animal cells) - provides the force to divide the cell in two, composed of
actin and myosin
Stages of Cell Division
Cell division = mitosis + cytokinesis

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I. Mitosis
Consists of 5 distinct stages:
Chromosomes condense paired chromatids
Cytoplasmic microtubules disappear
Spindle microtubules begin to grow from the centrosomes
Kinetochores assemble at the centromere of each chromatid
Nuclear envelope breaks down
Centrosomes move to opposite poles of the cell spindle poles
Spindle microtubules enter the nuclear region
Some microtubules attach to kinetochores (kinetochore microtubules)
Some microtubules from opposite poles overlap and attach (polar microtubules)
Chromosomes align in a metaphase plate
Chromatids separate (release of cohesin linkeage) and move toward opposite spindle
Kinetochore microtubules shorten
Polar microtubules elongate
Chromosomes reach spindle poles
Chromosomes decondense
Nucleolus begins to reappear
Nucleus begins to reform
Contractile ring begins to form
II. Cytokinesis
Contractile ring contracts (purse string-effect)
Cleavage furrow forms and the cell divides into two cells
Kinetochore microtubules disappear
Polar microtubules disappear, except for the midbody
Cytoplasmic microtubules reappear
Mitotic Spindle
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