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Cell Cycle & Checkpoints
Lecture 1
Eukaryotic organisms
• Heritable information is passed to the next
generation via processes that include cell
cycle and mitosis or meiosis plus
fertilization
Cell Reproduction
• Cell division
(MITOSIS)
– process that forms
new cells from one cell
– results in two cells that
are identical to the
original, parent cell.
Importance of Cell Reproduction
• Growth (increase in size)
• Repair (replace dead or damaged cells)
• Asexual reproduction
Cell Cycle
• Sequence of
growth and
division of a cell
– Growth period=
Interphase
– Nuclear Division=
mitosis
Interphase
• Cell grows in size
• Carries on
metabolism
• Chromosomes
duplicate (synthesis
of DNA)
• Preparation for
mitosis (actual
division into 2
identical cells)
INTERPHASE = G1, S, G2
G2- Gap 2
Grow
Produce molecules &
organelles needed
for cell division
MITOSIS
S- Synthesis
DNA replication
G1- Gap 1
Grow by producing
proteins & organelles
G0Cell leaves cycle
and stops dividing
Most body cells in
this phase
Some can return to cycle with signal
(external or internal signals)
(Ex; Liver cells respond to injury)
Some never divide again
(Ex: Mature nerve, muscle cells)
Cyclin-dependent kinases (Cdk’s) are
present all the time
but inactive unless combined with cyclins
KINASESEnzymes that work
by adding a
phosphate group
to other molecules
Presence of MPF (mitosis promoting factor) triggers
passage
past G1 & G 2 checkpoints
Cyclin levels
change throughout
cell cycle
Fluctuating levels
of different
Cyclin-Cdk complexes
seem to control
all stages of
cell cycle
Cancer
Lecture 2
•
•
•
•
CANCER CELLS
Don’t respond to control signals
Lose density-dependent inhibition
Lose anchorage dependence
Telomerase enzymes maintain/replace
telomeres
Transformationprocess that changes
a normal cell into
a cancer cell
Telomeres protect DNA from being degraded
Telomeres become shorter with each
replication; shorter in older cells
Telomerase enzyme lengthens telomeres
Cancer cells have increased telomerase activity
2009
Nobel Prize
Physiology/Medicine
Discovery of Telomeres
Jack Szostak
Carol Greider Elizabeth Blackburn.
Most cells divide 20-50 times in culture;
then stop, age, die
Cancer cells are “immortal”
-HeLa cells from a tumor removed from
a woman (Henrietta Lacks) in 1951 are
still reproducing in culture
http://www.sanger.ac.uk/Info/Press/gfx/081223_cells_300.jpg
Phases of Mitosis
Lecture 3
Phases of Mitosis
• Occurs after DNA replication
• Mitosis is a continuous process of
replication, alignment and separation.
• Produce 2 genetically identical cells (each
cell has the same genome)
Phases of Mitosis
•
•
•
•
Prophase
Metaphase
Anaphase
Telophase
Prophase
• Chromatin (DNA) coils to form visible
chromosomes
– Sister chromatids visible
• held together by centromere
Spindle fibers
Disappearing
nuclear envelope
Doubled
chromosome
Metaphase
• Chromosomes line up in middle of cell
(chromosome alignment)
Centromere
Sister
chromatids
Anaphase
• Centromeres split
• sister chromatids pulled apart to opposite
sides of cell
Telophase
• Two daughter cells form
• Cells separate
• Cells proceed into the next interphase
Nuclear
envelope
reappears
Two daughter cells are formed
Cytokinesis
• end of telophase
• cytoplasm and organelles divide
• Occurs differently in plants and animals
Results of Mitosis
• Unicellular organisms remain as single cells.
• In multicellular organisms, cell growth and
reproduction result in groups of cells that work
together as tissue to perform a specific
function.
CellsTissuesOrgansOrgan Systems