19. 5
How does te nuclear envelope disassembly?
1. When the mitotic CDKs are activated at the end of G2, they phosphorylate specific serine residues in all three nuclear lamins. 2. This phosphorylation together with phosphorylation of lamin B by protein kinase C, causes depolymerization of the lamin intermediate filaments 3. Depolymerization of the nuclear lamins leads to disintegration of the nuclear lamina and contributes to disassembly of the nuclear envelope
Mitotic CDKs promote their own activation through what?
2 positive feedback loops that inactivate Wee1 kinase and activate Cdc25 phosphatase (
What does the process centrosome disjunction create?
2 separate centrosomes
What is centrosome maturation?
A process where the single centrosome ( the cell has during G1) create a mitotic spindle by duplicate into two centrosomes
How many centrioles does G1 cells contain?
A single pair (altså 2)
When does the formation of the mitotic spindle begin?
At the G1-S phase transision with the duplication of the centrosomes.
Which is the dominant error-correcting kinase for chromosomes along most of the spindle, Aurora A og B?
Aurora B
How are the mitotic CDKs kept inactive?
By inhibitory phosphorylation of the CDK subunit until the completion of DNA replication
What happens when the function of the codensin is lost?
Chromosomes do not condense and sister chromatid tangles are not resolved
What facilitates chromosome segregation?
Chromsome condensation
In which phase does centrosomes duplicate?
During S phase
In which phase do centrosomes separate?
During mitosis
During what phase is the nuclear envelope broken down?
During prometaphase
During what phase have the centrosomes moved apart form each other?
During prophase
Aurora kinase family members Aurora A and Aurora B play key roles in mitotic spindle formation. What do they ensure?
Ensuring that chromosomes attach correctly to the mitotic spindle so that they are segregated accurately during mitosis.
Where are the centrosomes that nucleate (former en kerne) the mitotic spindle located during interphase?
In the cytoplasma
What it gamma-tubulin?
It is a specialized type of tubulin i centrosomes. They form specific ringlike complexes (gamma-TuRCs)
What is the mitotic spindle made of?
Microtubules that attach to chromosomes via specialized protein structures known as kinetochores, which form at the central centromeric region of chromosomes.
What induce entry into mitosis in all eukaryotes?
Mitotic CDKs
What faciliate the association of condensin with chromosomes?
Mitotic CDKs and Aurora B, which phosphorylate histone H2A, allowing condensins to bind chromatin.
What does gamma tubulin ringlike complexes (gamma-TuRCs) together with a variety of associated proteins, have the ability to do?
Nucleate (forme en kerne) microtubules and form a bipolar spindle
What mechanism is used for the cell to know when its sister chromatids are correctly attached to microtubules?
Tension in the kinetochores When sister chromatids are correctly attached to microtubules, their kinetochores are under tension.
How does the cell measure whether or not kinetochores are under tension?
The Aurora protein kinase family members Aurora A and Aurora B and their associated regulatory factors sense kinetochores that are not under tension and sever these microtubule attachments, giving cells a second chance to get the attachment right.
What happens to the mature centrosomes when the cell enters prophase?
The centrsomes separate from one another and move to opposite sides of the cell nucleus, where they create the mitotic spindle.
What results in the abrupt and irreversible transition from G2 to mitosis?
The combination of two positive feedback loops — one that activates a CDK1 activator (Cdc25C), and one that inhibits a CDK1 inhibitor (Wee1)
What is the centrosome cycle?
The events where the single centrosomes duplicate and form a mitotic spindle whereafter when the mitosis is completed, the centrosomes re-form its G1-like structure
What do Aurora and Polo-like kinases plus mitotic CDKs trigger?
The following events: 1. Chromosomes condense and attach to the mitotic spindle, 2. The nuclear envelope is disassembled 3. Almost all organelles are rebuilt or modified
What is PIk1 critical for?
The formation of the mitotic spindle and for chromosome segregation.
For chromosomes to be accurately segregated during mitosis, what must they attach to?
The mitotic spindle in such way that one kinetochore of each sister chromatid pair attaches to microtubules emanating from opposite spindle poles
What surrounds the chromosome during interphase?
The nuclear envelope.
What functions as the majr microtubule nucleating center of the cell?
The single centrosome the cell contain during the G1 phase
What are the ends of the mitotic spindle always referred to as?
The spindle poles
What is the function of the mitotic spindle?
Their function is to segregate (adskille) chromosomes so that the sister chromatids separate from each other and are moved to opposite poles of the cell
What is the mitotic spindle also called?
Tte mitotic apparatus
What is an amphitelic attachment?
When the kinetochores of each sister chromatid are attached to microtubules coming from opposing centrosomes
Does chromosome condensation results in a dramatic reduction in chromosome length, up to 10,000-fold in vertebrates?
Yes
Is the centrosome cycle coordinated with the cell cycle?
Yes, very
What do microtubule force to do, when microtubules are attached correctly to kinetochores,
icrotubule forces pull Ndc80 away from Aurora B, and the kinase can no longer phosphorylate Ndc80
What are centrioles?
short, microtubule-based structures arranged orthogonally to each other and surrounded by proteinaceous pericentriolar material (PCM)