Transcript mitosis & cell cycle

The Cell Cycle
When do cells divide?
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Reproduction
Replacement of damaged cells
Growth of new cells
In replacement and growth cell divisions
how should daughter cells compare to
parent cell?
• The daughter cells should be identical
copies of the parent cell.
How can identical daughter
cells form?
• The genome must be copied and then
divided such that each daughter cell
gets one of the copies.
• Genome = all the genes in an organism
Bacterial Reproduction
• How do bacterial cells reproduce?
Important terms in eukaryotic
cell division
• Chromosome = threadlike structures
that are composed of DNA + protein
• replication = process whereby DNA is
identically copied (before cell division)
• mitosis = division of the nucleus
• cytokinesis = division of the cytoplasm
• chromatin = DNA + protein complex
that is thin and fibrous; it will condense
into distinct chromosomes during cell
division
• Chromatid = after replication the
chromosome consists of 2 sister
chromatids joined at the centromere.
• Centromere = specialized region of the
chromosome, where chromatids are
joined. Each chromosome has one
centromere.
The Cell Cycle
Interphase
• Around_____of cell cycle is spent in this
phase
• G1 = first growth phase
• S = synthesis phase, DNA synthesis
(replication) occurs here
• G2 = second growth phase
G2 phase of Interphase in
animal cells:
• Nuclear envelope is visible
• One or more nucleoli are present
• Centrioles are replicated and the 2 pairs
are near nucleus
• aster forms around each pair of
centrioles
• chromosomes are loosely packed into
chromatin fiber, not distinguishable
General Overview of Mitosis
Late Interphase:
Prophase:
• In the Nucleus:
• Nucleoli disappear
• chromosome fibers condense into
discrete chromosomes
• each chromosome consists of 2 sister
chromatids joined at the centromere
In the Cytoplasm:
• mitotic spindle begins to form
• spindle consists of microtubules
arranged between the centrosomes
• centrosomes move apart due to
lengthening of microtubules
Prometaphase:
• Nuclear envelope breaks apart
• each chromatid has specialized
structure called kinetochore located at
the centromere region
• kinetochore microtubules (km) interact
with chromosomes at the kinetochore
region
• The km’s cause the chromosomes to
move
• nonkinetochore microtubules radiate
from each pole
Metaphase
• Chromosomes move to the metaphase plate
and line up there
• the centromeres of the chromosomes are all
aligned on the metaphase plate
• each sister chromatid of one chromosome,
has a kinetochore microtubule attached to it
from opposite poles
• kinetochore microtubules + nonkinetochore
microtubules = spindle fiber
Anaphase
• Kinetochore microtubules shorten and
non-kinetochore microtubules lengthen
• Centromeres divide and each
chromosome has no sister chromatid
component
• the shape of the cell elongates into an
elipse
• chromosomes are pulled to the opposite
poles
Telophase
• Nonkinetochore microtubules continue
to elongate the cell
• new daughter nuclei form at the two
poles
• new nuclear envelopes are formed
around the chromosomes
• nucleoli reappear
• chromosomes uncoil into chromatin
fiber
• last phase of mitosis
Cytokinesis
• Begins before telophase has completed
• evidenced by cleavage furrow in animal
cells and cell plate in plant cells
Mitochondrial Division
Evolution of mitosis:
Bacterial cells
Dinoflagelates;
chromosomes attach to
nuclear envelope.
Diatoms;
nuclear
envelope stays,
microtubules
inside nucleus
Most other
eukaryotes;
spindle forms
outside of
nucleus, and
nuclear envelope
breaks apart
Examples
Dinoflagellates
Diatoms
Checkpoints
in the cell
cycle: If it
passes the G1
checkpoint
cell divides if
not enters G0
phase and
does not
divide
Cyclin protein
levels fluctuate
according to cell
cycle stage.
When cyclin is
high the Cdk
attaches and
phosphorylation
leads to
breakdown of
nuclear
envelope. Later
MPF initiates
cyclin breakdown
Cancer cells
• How does abnormal cell division of
cancer cells differ from normal cell
division?
• Cancer cells are not under density
dependent inhibition
• Continue to grow until all nutrients are
used up
• Cancer cells are immortal, do not
shorten telomeres.
• Cancer cells often have a mutated p53
gene.
p53 Gene
• Known as the tumor suppressor gene
• Found on the 17th chromosome
• Codes for a p53 protein (393 amino
acids long)
• The protein does three things– Arrests growth by stopping the cell cycle
– Activates DNA repair enzymes if mutations
are detected
– Causes apoptosis (cell death) if cell is
irreparable
– http://www.youtube.com/watch?v=witLM--