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CH12: The Cell Cycle (Mitotic Phases & More Organelles (Mitotic…
CH12: The Cell Cycle
Mitotic Phases & More Organelles
phases
Interphase
G1
cell grows , make more organelles
S
copy chromosomes (collection energy, expand nucleus size)
G2
grows more
Prophase
chromatin condensed into chromosomes, microtubules start appearing
Prometaphase
nuclear envelope disappearing, microtubules attached to kinetochore
Metaphase
chromosomes being moved to midline by tug-of-war of microtubules
Anaphase
cohesin disappears (by enzyme
separase
), sister chromatids move toward diff poles
Telophase
cell division almost over, marked by cytokinesis, nuclear membrane reappearing, chromosomes less condensed
Mitotic Spindle
begin to form during
prophase
lengthen: gaining
tubulin
subunits
shorten: losing
tubulin
subunits
centrosome
: where mitotic spindle meets
duplicates during
interphase
a pair of
centrioles
found in the centre of centrosomes
aster
: short microtubules surrounding the centrosome
PAGE 249
Kinetochores
attach in each side of centromere
HOW IT WORKS??
"PAC-MAN" mechanism
motor proteins in kinetochore "walk" sis chromatids towards pole
motor proteins in microtubules "reeled in" the sis chromatids
nonkinetochore microtubules: lengthen cells during anaphase
Cytokinesis
cleavage
first sign:
cleavage furrow
interaction of actin-myosin: contractile ring of microfilaments
only happens in animal cells
plant cells: form
cell plate
during cytokinesis (basically Golgi vesicles)
surround the entire plasma membrane
Bacteria Binary Fission
cell division starting point ->
origin of replication
(location where DNA replicates in chromosome)
2 origins total
chromosomes replicate in origin
1 origin moves to the other side, cell elongates
plasma membrane picked inward by tubular-like protein
2 daughter cells produced
Evolution of Mitosis
bacterial binary fission
slowly transform to mitosis
since appearance of nuclear membranes & gnome modified
nuclear division in prokaryotes
dinoflagellates, diatoms, some yeasts
How does most cell divisions results in genetically identical daughter cells?
Cellular Organization of the Genetic Material
genome
: DNA's ability of storing genetic info
chromosomes
: DNA that is packed with the help of histones (proteins)
hv specific colour
made up of
chromatin
vary in degree of condensation
every eukaryote has its own # of chromosomes
e.g. humans hv 46 chromosomes, gametes hv 23
How is the Distribution of Chromosomes during Eukaryotic Cell Division?
chromatin ----(
condense
)----> chromosome
each hv identical DNA molecules
cohesin
: protein holds sister chromatids together
centrometre: region where sister chromatids meet (location of kinetochores as well)
mitosis: cell division producing identical daughter cells
followed by
cytokinesis
: division of plasma membrane
produce 200million somatic cells in fertilized eggs
meiosis
produce 4 non-identical daughter cells
only for gametes
CELL DIVISION [crucial] function
produce offspring with identical characteristics with parents
How does the Eukaryotic Cell Cycle Regulated by a Molecular Control System?
cell cycle control system
cellular molecules that triggers & lead key events in cell cycle
regulatory molecules: protein
kinases & cyclins
(pg 255)
cyclins-dependen kinases (cdk) needs to be
activated
by cyclins --> produce MPF (M-phase promoting factor)
MPF promotes mitosis by providing changes (e.g. nuclear membrane disappearance)
cyclins are produced @ the end of S phase, degrade during M phase
checkpoints
G2-M
allow cell to go from interphase to mitosis
M
check whether all chromosomes hv attached to spindle
S-G1
crucial point
cell cycle continues / back to G0
influence: external factors and growth factors
contributing factors
size of cells
nutritional conditions of cells
growth factors