LOOs 13 Flashcards
What are the different stages of M-phase?
two main stages:
-mitosis (prophase, prometaphase, metaphase, anaphase, telophase)
-cytokinesis
How does cohesin and condensin contribute to mitotic chromosome structure?
cohesin - provide cohesion to allow appropriate attachment of chromosomes to spindle poles
condensin - helps with DNA compaction and generation of condense chromosomes into chromatids
Does the centrosome “replicate” during the cell cycle? If so – how?
Yes, little is known but is during S-phase in a semi-conservative manner (parallel to DNA replication)
Be able to visualize and define the mitotic spindle.
a bipolar array of microtubules, which pulls sister chromatids apart in anaphase, thereby segregating the two sets of chromosomes to opposite ends of the cell, where they are packaged into daughter nuclei
( controls chromosome movement during mitosis)
What is a ‘spindle pole’?
the region of the cell where the centrosome is located and toward which the chromosomes will move
What are the three classes of microtubules in the mitotic spindle?
Kinetochore microtubules - plus ends are attached to sister-chromatid pairs at large protein structures called kinetochores, which are located at the centromere of each sister chromatid to the spindle poles
Non-kinetochore microtubules (aka interpolar microtubules) - short and unstable microtubules are densely packed between the poles, cross-linked by various proteins to form a dynamic and adaptable scaffolding network that provides structural stability to the spindle
Astral microtubules - radiate outward from the poles and contact the cell cortex, helping to position the spindle in the cell
Do the properties of microtubules change during M-phase?
yes, entry into mitosis signals a change in microtubule dynamics due to:
-increased nucleation rates
-phosphorylation of microtubule associated proteins that alter microtubule activity
What are the different types of mitotic spindle microtubule motor proteins?
1) kinesin 5: associate with antiparallel microtubules to slide them in opposite directions (tetramer moving to + end)
2) dynein : pull spindle poles toward cell cortex and away from each other
3) kinesis 14: cross-link antiparallel microtubules at center and pull poles together (moves toward - end)
4) kinesin 4/10: push attached chromosomes away from the pole , or the pole away from the chromosome
How are the different types of mitotic spindle microtubule motor proteins related and how are they different?
-They are related in that they all involve pulling the microtubules, spindle poles, and chromosomes
-They are different in which one of these they will pull and in one direction
How does Ran-GTP contribute to bipolar spindle assembly?
Ran-GTP releases microtubule regulatory proteins from the protein complex in the cytosol. This stimulates the nucleation and stabilization of microtubules around chromosomes
What is the kinetochore?
a giant, multilayered protein structure that is built at the centromeric region of the chromatid
How are microtubules attached to the kinetochore?
Plus ends of kinetochore microtubules bind to kinetochore, kinetochore is anchored by Ndc80 complex (rod shape protein) and Ndc80 interacts with sides of kinetochore microtubules
Bi-orientation
the attachment of sister chromatids to opposite poles of the mitotic spindle, so that they move to opposite ends of the cell when they separate in anaphase.
How is Bi-orientation achieved during M-phase?
trial and error, eventually the tension of the spindles on the chromatids make the structure stable
Mechanistically, how does the ‘tension sensor’ function?
phosphorylation of Ndc80 by Aurora B kinase decrease its affinity for microtubule plus end making the attachment to the kinetochore slippery. if microtubule is successful Aurora B kinase has no access to Ndc80 bc the tension pulls Ndc80 out of Aurora B kinase reach
