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MITOSIS
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1. The number of chromosomes varies within species
2. Chromosomes are composed of chromatin
a. Complex of 40% DNA and 60% protein
b. Contains some RNA since DNA is the site of RNA synthesis
3. DNA exists as a long double-stranded fiber
4. DNA coiled to fit into a smaller space than otherwise possible
5. DNA resembles a string of beads 5
a. DNA is coiled around histone polypeptides every 200 nucleotides
b. Eight histones form a core called a nucleosome
c. Basic, positively charged histones attract negatively charged
DNA
d. String of nucleosomes further wrapped into supercoils
1. Heterochromatin
a. Highly condensed portions of chromatin
b. Some portions permanently condensed to prevent DNA
expression
2. Euchromatin
a. Remainder of chromatin condensed only during cell
replication
e. DNA is uncondensed to allow for gene expression
6. Chromosomes vary widely in appearance
a. Position of the centromere
b. Relative length of the arms on either side of the centromere
c. Size and staining properties
d. Position of additional constricted regions along arms
G1
S
(DNA synthesis)
G2
1.
M phase: mitosis
1. Microtubular apparatus assembled
2. Sister chromatids move apart from
one another
3. Mitosis subdivided into four
continuous stages
1. Interphase
a. G1 phase: cells undergo major portion of growth
b. S phase: chromosome replicates to produce sister
chromatids
1. Remain attached at the centromere
2. Location specific to each chromosome
c. G2 phase: chromosomes begin process of
condensation
1. Condensation of DNA
2. In G2 cells assemble machinery used to move
chromosomes apart
a.
Animals replicate centriole, nuclear
microtubuleorganizing centers,mitochondria,ect
b.
Eukaryotic cells synthesize tubulin,
microtubule
protein component
3. Restructuring of microtubules and assembly at
spindle
d. Go phase:
1. Prophase
a. Individual condensed chromosomes visibleCondensation continues
b. Ribosomal RNA synthesis ceases, nucleolus
disappears
c. Spindle fibers begins to assemble(microtubules)
d. In plant cells, spindle apparatus forms
e. Nuclear envelope breaks down
METAPHASE
a. Begins when pairs of sister chromatids align
in center of the cell
b. Chromosomes align along the metaphase
plate
c. Centromeres are equidistant from each pole
d. Centromeres divide at the end of metaphase
e. Centromere splits in two-All centromeres
divide in synchrony
ANAPHASE
a. Shortest phase, during which sister chromatids
separate
b. Chromatid drawn to pole to which it is attached
c. Separation achieved by two simultaneous
microtubular actions
d. Poles move apart
1. Microtubular spindle fibers slide past one
another. Kinetochore
2. Microtubules are anchored at poles which are
pushed apart
e. Centromeres move toward poles-Shortening not a
contraction. Microtubules shorten as tubulin
subunits are removed
TELOPHASE
 Reform Nuclear membrane-karyokinesis
a. Separation of chromatids completes division of replicated
genome
b. Nuclear envelope re-forms around each new set of
chromosomes
e. Chromosomes begin to uncoil to allow gene expression
f. rRNA genes begin transcription, nucleolus reappears
g. Mitosis(Mphase) Complete at End of Telophase
h. Replicated genome divided-two new nuclei-opposite ends
of cell
i. Organelles assort to regions that will become separated
CYTOKINESIS
C phase: cytokinesis-Plants and Animals Progresses Differently
a. Animal cytokines
1. Cell is pinched in two by a constricting belt of microfilaments
2.Actin filaments slide past one another
3.Produces distinct cleavage furrow around circumference of
cell
4.
Furrow deepens until the cell is literally pinched in two
b.
Plant cytokinesis
1.Rigid cell wall, cannot be deformed by microfilament
contraction
2.Membrane components assembled in the cell interior
3.Expanding partition called the cell plate
4.Grows outward to the interior surface of the cell membrane
5.
Cellulose then added on the membrane making two
new cells
GROWTH FACTORS
 SIGNALING PATHWAYS--LINK CYCLIN KINASES TO
PROCESS.
 ANAPHASE SISTER CHROMATIDS STAY T
OGETHER UNTIL KINETOCHORES ARE PROPERLY
ATTACHED
 ANCHORAGE DEPENDANCE
 DENSITY DEPENDENT FACTORS-EXTERNAL
FACTORS
 CELL CROWDING -REACHES POINT WHERE TOUCHSTOP
 NOT ENOUGH NUTRIENTS TO TAKE CARE OF MORE
 FACTOR PLATELET-DERIVED GROWTH FACTOR



DERIVED FROM PLATELETS
BIND TO PDGF RECEPTORS ON MEMBRANE
TRIGGER THRU SIGNAL TRANSDUCTION PATHWAY TO STIMULATE
CELL TO PASS G1 CHECKPOINT AND DIVIDE.
FACTOR PLATELET-DERIVED
GROWTH