Mitosis Flashcards
Mitosis
shortest part of the cell cycle
Ensure accurate partitioning of the genome to daughter cells
6 phases
Prep for mitosis sequence
- before cell division cell has 6 chromosomes, 2 sets of 3 each
- Chromosome repl produces 6 pairs of sister chromatids
- Nucleus breaks apart and repl chromosomes condense in prep for mitois
- SIster chromatids separate during mitosis, and 2 cells formed during cytokinesis
Cyclins regulate cell cycle via
CDKs
How do cyclins regulate
bind to and activate CDKs enzymes
Cyclin-CDKs phosphorylate
key players in the cell cycle
Which initiate dna repl
Also phosphorylate lamins- nuclear envelope breakdown
how are cyclins targeted for destruction
ubiquitination
Ubiquitination
ubiquitin added to a protein, destruction complex targets that protein eg APC/C
2 phases of repl and separation
- repl all the dna, once: S phase
2. Divide copies from one nucleus into 2: mitosis
homologous chromosomes
one paternal, one maternal
sister chromatids
two copies of replicated chromosome
two maternal, two paternal (together)
What keeps replicated sister chromatids together
cohesion rings
How do you replicate dna only once
origins of repl ‘fire’ once per S phase
Cyclin -cdk complexes destroyed by APC/C
If you remove a protein that activates the APC/C, Emi1
Replication origins keep firing
Cells never enter M phase
When does polarisation of microtubules into bipolar spindle begin
In S/G2 with duplication of the centrosome (MTOC)
centrosome
centrioles and mass of proteins called pericentriolar materia
centriole
replicate in S/G2
split into 2 and travel to opposite poles at the start of mitosis
prophase
chromosome condensation:
- cohesin holds sister chromatids together
- condensins have a similar ring structure to cohesins, further loop chromatin into tight bundles
centrosomes move apart, begin to form spindle
nucelar envelope intact
Prometaphase
nuclear envelope breaks down:
- phosphorlyation of lamins by cyclin B-CDK1
- fragments from vesicles
- vesicles contain lamin B, not lamin A/C
- nuclear pore complexes (phosphorylated) diassemble
centrosome attaches to chromatids via kinetochore
Metaphase
sister chromatids line up on metaphase plate
Dynamic instability- MTs grow slowly by adding subunits, shrink rapidly
Physical force from dynamic MTs orients mitotic spindle
mitotic spindle orientation
sensitive to physical constraints: reorients when microtubules cut with a laser
spindle orientation important for tissue patterning/development
What happens if tissue patterning goes wrong
cancer
Parallel division of cells
stem cells
stay in one layer
Perpendicular division of cells
differentiation
cells travel up through the layers
kinetochore
protein complex linking chromatin and microtubules
CENP-B protein binds 17 bp sequence in centromeric chromatin
Sensor proteins monitor attachment to microtubules
