Intracelluarly - Mitosis Flashcards
Prophase
The first stage of mitosis where chromosomes condense and the G2 phase ends.
What causes chromosomal condensation?
Modifcaitons to the histones the DNA wraps like acetylation and phosphorylation.
How does chromosome compaction affect its morphology?
Decrease length and increased thickness.
What causes transcriptional shut down during comapction?
TF displacement.
What events occur in prophase?
Chromosome Compaction
Nuclear Envelope dispersal
Spindle formation
How is rRNA transcription arrested?
Phosphorytlation by CDK1 cyclic B kinase of pol1 TF and NPM/B3.
What happens to NPC and lamin fibre components in propase?
CDK1 hyperphosphorylates them.
Why is slowing down of protein synthesis during prophase important?
It slows mRNA transit to proect it during mitosis
How do cytoskeletal components change during prophase?
MT and microfilaments largely dissolve by PHOS and only actin remains for cytokinesis.
How does prophase conserve cytoskeletal material?
Using it to construct spindle and cytokinetic machinery
Why is spherical formation after cytoskeltal dissapearance important in prophase?
Promotes symmetrical diffusion for uniform distribution.
How is diffusive randomness promoted in prophase?
Decrease of cytoplasmic viscoscity by polymer solublisation.
Why are enhanced diffusive capabilities important in prophase?
Equipartinioning of cell resources for cytokinesis.
Centrosomes
A cellular organelle of two centrioles, regulating MT formation
Prometaphase
This is where nuclear envelope has finalised dispersal and nuclear structures are exposed.
What are some of the structural components of the Kinetochore?
NDC80, KNL1, Dyenin and Kinesin.
What do motor proteins on MT do?
Influence chromosomes position and MT dynamic instability by force generation.
How does dyenin relate to the MC?
It associates its minus end.
Merotelic Kinteochore Attachment
An error when a single KC attachs to MT emanaiting from both spindle poles.
Why is MT miss-binding common?
There are more tubulins associated with MT walls, thus more chance they bind to KC.
What faciliattes KC MT attachment?
Action of Dyenin and Kinesin
How does Kinesin assist KC and MT attachment?
It ferries chromosomes towards middle of spindle using parralel adjacent microtubules.
How do Dynein and Kinesin work together to facilitate KC and MT attachment?
By reorientation of the chromsome in a way maximising attachment.
Spindle Assembly Checkpoint
A mechanism controlling genomic stabiltiy through MT attachment modulation.
How does the SAC facilitate its function?
Represses anaphase onset until correct chromosome segregation.
What is the mechanism behind SAC activation?
It remains active so long as kinetochore is unattached, thus inhbition occuring when final KC attaches, activating separase
Separase
An Enzyme dissolving sister chromatid associations, initiating anaphase.
What does Separase target?
CDC20 of APC/C
What does separase action result in?
Impediment of CDC20 ability to act on Cyclin B and Securin, which should prevent their destruction.
What happens to CDK1 in SAC?
Cyclin B inactives it when Cyclin B is protelysed by CDC20, promoting mitotic exit.
How does CDK1 facilitate its function?
Controls mitotic phases by PHOS of regultaors, also restraining proteins later required.
Functions of the spindle?
Chromosomal segregation
Kinetochores
Mediators of MT and sister chromatid attachment, facilitating correct equtorial segregation.
How do KC facilitate with the centromere loci?
CCAN is recruited to CENP-A histone variants
Constitutive Centromere-Associated Netowrk
A protein network in the KC, localising to centromeres and facilitating chromatin and MT binding.
MT Dynamic Instability
The constant assocaition and disassociation of tubulins from the plus end of the protofilament.
What is the general structure of MT?
Beta and Alpha tubulin dimers, plus ends free in the cytoplasm and minus ends anchored.
What is MDI mediated by?
GTP hydrolysis of beta tubulins
What happens when GTP is hyrdolysed to GDP?
CC where b-tubulin curves outward from the wall of the MT.
What happens to A-tubulin in MDI?
GTP remains bound, providing lateral interactions for structural integrity, resisting curvature.
What facilitates MTOC MT nucleation?
y-tubulin MT nucleator complex forming open ring models where MT protofilaments stem
What is MT polymerisation and depolymerisation facilitated by?
MAPS and Kinesin-13
Metaphase
The stage where chromosome pairs are fully condensed and are bound to the mitotic spindle, alligned at the metaphase plate.
Metaphase Plate
An equatorial plane of the spindle having chromosomes oriented upon it.
How is anaphase onset?
Cohesins cleavage between sister strands
Anaphase
Chromosomal segregation and their migration to opposite cell poles.
Cytokinesis
Splitting of a cell into two daughter cells.
What is the process of cytokinesis?
Cleavage furrow formation, resulting in two daughter cells connected by an intracellular bridge, then bridge absicion.
Rab11/FIP3 endosomes
Initate abscission process at the IB in midzone through actin cytoskeltal disassembly.
