Mitosis Flashcards
(31 cards)
What are cyclins?
Proteins associated w/ the cycle of cell division
- initiate certain processes of mitosis
They accumulate in diff stages of cell cycle
What do cyclins do?
What happens then?
How are lamins involved?
Bind & activate cyclin dependent kinases (CDKs)
Cyclin-CDKs phosphorylate key players in cell cycle
–> initiates DNA replication
Lamins initiate nuclear envelope breakdown
How are cyclin levels reduced?
Targeted for destruction by ubiquitination
due to APC/C = anaphase promoting complex/cyclosome
What is the goal of mitosis?
To ensure the accurate partitioning of the genome to daughter cells
How many phases are there in mitosis?
What are they?
6
Prophase Prometaphase Metaphase Anaphase Telophase Cytokinesis
Briefly, what happens in the replication & separation of the genome?
- Replicate all DNA once only
= S-phase - Divide copies from 1 nucleus into 2
= M-phase
What is PCNA?
= Proliferating Cell Nuclear Antigen
Part of DNA replication complex
- co-factor of DNA pol
Has a speckled texture in S-phase
What is the role of cohesin in DNA replication?
Cohesin rings keep replicated sister chromatids together
- as replication machinery passes the clamps move along & hold chromatids together
How is DNA only replicated once?
Origins of replication fire once per S-phase
- then the Cyclin-CDK complexes are destroyed by APC/C
What happens if the protein that activates APC/C is removed?
Replication origins keep firing
–> cells never enter M-phase
What is the centrosome also known as?
MTOC
= microtubule organising centre
What happens during the dividing of the genome from 1 nucleus into 2?
Process begins in S/G2 phase w/ duplication of centrosome
–> polarisation of microtubules into a bipolar spindle
What are centrosomes?
Centrioles + pericentriolar material (= mass of proteins)
What are centrioles?
Organelles
- Identical to basal body at base of cilia
- replicated in S/G2 phase
What do centrioles do at the start of M-phase?
Pairs of daughters travel to opposite sides of nucleus
What happens in prophase?
- Chromosome condensation begins
- cohesin holds sister chromatids together
- condensins further loop chromatin into tight bundles - Centrosomes move apart & mitotic spindles begin to form
(Nuclear envelope still in tact)
What happens in pro metaphase?
- Condensed chromosomes attach to microtubules
2. Nucleus envelope breaks down
What causes the nuclear envelope to breakdown?
- Phosphorylation of lamins by cyclin B-CDK1
- Envelope fragments form vesicles
- Vesicles contain lamina B, but NOT lamina A/C - Nuclear pore complexes dissemble
What happens in metaphase?
- Sister chromatids line up on metaphase plate (=equator)
- Dynamic instability
- -> microtubules grow slowly & shrink rapidly - Physical force from dynamic MTs orients the mitotic spindle
What is mitotic spindle orientation sensitive to?
What is the orientation important for?
Physical constraints
- reorients when Mts are cut w/ a laser
Tissue patterning
How does mitotic spindle orientation affect the type of cell produced?
In basal layer (stratified epidermis):
Parallel division
–> stem cells
Perpendicular division
–> differentiation
What is the kinetochore?
A protein complex which links chromatin & microtubules
What is the kinetochore made up of?
Structural & signalling proteins:
> CENP-B protein binds 17-bp sequence in centromeric chromatin
> Sensor proteins that monitor attachment to MTs
- can sense tension
What is the Mitotic Checkpoint Complex (MCC)?
The spindle assembly checkpoint
- it inhibits APC when kinetochores are exposed
(prevents separation of duplicated chromosomes until each chromosome is properly attached to the spindle apparatus)
