Transcript Chapter 12 notes

Chapter 12
The Cell Cycle
Roles of cell division
• reproduction
• growth/maintenance
• repair
Eukaryotic chromosome
Cell Cycle
Cell Cycle
Interphase – period when the cell is not dividing
consists of:
G1 – gap (growth period)
S – synthesis of DNA
G2 – gap (growth, preparation for division)
Mitosis (M)
Prophase – centrioles migrate to opposite poles,
nucleolus breaks down, spindle begins to form,
chromatid pairs get shorter, compact, & more
visible
Prometaphase - nuclear membrane breaks
down, spindle fibers extend to centromeres
Metaphase – spindle fibers have attached to
kinetochore of ea. sister chromatid at the
centromere; sister chromatids are aligned at
metaphase plate (equator)
Mitosis (M)
Anaphase – ea. chromatid of sister chromatid pair
is separated and pulled toward opposite poles
Telophase – nuclear membrane & nucleolus
reappear, spindle breaks down, chromosomes
get longer, thinner
cytokinesis – division of cytoplasm
Differences in plant and animal cell
cytokinesis
In animal cells, a contractile ring forms a
cleavage furrow as the membrane pinches
in to divide the 2 daughter cells
In plant cells, a cell plate forms as vesicles
of the Golgi pinch off containing cell wall
material, migrate to the metaphase plate,
elongate, & fuse to form a new cell wall to
separate the 2 daughter cells
Cleavage furrow in an animal cell
Cell plate in a plant cell
Differences in prokaryotic &
eukaryotic cell division
Prokaryotes – (bacteria) divide by binary fission;
circular DNA in a single chromosome
1) DNA replicates
2) Each copy is attached to cell membrane
at opposite ends of the cell
3) Cell membrane forms between the 2
daughter cells being produced as growth
continues
4) membrane pinches inward, new cell wall
material is deposited between 2 daughter cells
Binary fission
Differences in prokaryotic &
eukaryotic cell division
Eukaryotes – (everything else) divide most
commonly by mitosis
Regulation of the cell cycle
• controlled by regulatory proteins
• checkpoints – critical points where go/no go
signals regulate processes
G1 checkpoint – “restriction point”
-if it passes this point, it is destined to
continue through division
-if it doesn’t pass this checkpoint, it goes
into G0
Regulation of the cell cycle
• kinase – enzyme that catalyzes transfer of PO4
from ATP to a target protein to activate or
inactivate it
Cdk’s – cyclin-dependent kinases (active only
when attached to a particular cyclin)
ex: MPF (maturation promoting factor)
• cyclins – concentrations change cyclically
Control systems
1) density dependent inhibition (contact inhibition)
cells stop dividing when they come into
contact with one another (usu. due to growth
factor decrease)
2) anchorage dependence – require attachment
to substrate (like ECM of a tissue)
Escaping normal controls
• cancer cells – unregulated growth of cells;
-divide indefinitely as long as nutrients are
available; “immortal”;
results in tumor (mass)
-benign – remains at original site
-malignant – ability to spread (cancer)
» unusual # of chromosomes
» aberrant metabolism
» lost attachments (abnormal surface changes)
Escaping normal controls
• metastasis – spread beyond original site