Cell Bio Exam 3 - Mitosis (Session 25)

what are the seven steps of mitosis that we discussed

1. interphase

2. prophase

3. prometaphase

4. metaphase

5. anaphase

6. telophase

7. cytokinesis

what parts of cell cycle are interphase and what occurs (2)

G1, S, G2

1. Chromosome duplication and cohesion

2. Centrosome duplication

what happens during prophase (4)

1. breakdown of interphase microtubule array and its replacement by mitotic asters

2. mitotic aster separation (centriole + centrosome)

3. chromosome condensation

4. kinetochore assembly

what happens during prometaphase (4)

1. breakdown of interphase microtubule array and its replacement by mitotic asters

2. mitotic aster separation

3. chromosome condensation

4. kinetochore assembly

what happens during prometaphase (2)

1. nucler envelope breakdown

2. chromosomes captured, bioriended and brought to the spindle equator

what happens during metaphase (1)

1. chromosomes aligned at the metaphase plate

during prophase how do two centrosomes move to opposite ends of the cell to create the spindle?

use of bipolar knesin-5 to walk towards the MT + ends which seperate the centrosomes.

What are the 3 types of MT in the spindle and how do they differ from the MT in interphase

Much ore dynamic

1. Kinetochore MT

2. Polar MT

3. Astral MT

What does Kinetochore MT do

Attatch to the kinetochore of the sister chromatids and helps seperate them later in Anaphase A

what does the Polar MT do

Attatches to top and bottom of the chromatids and helps seperate them and move them to spindle poles during Anaphase B

What does astral MT do

interacts with the cell corex for spindle orientation, doenst attatch to chromosomes

what is the centromere categorized by (3)

1. specific dna sequences

2. binding proteins

3. dna motifications

What are the three problems that are need to be solved to achieve metaphase organization.

1. having the kinetochores attach to MT plus ends

2. making sure the kinetochores are attached to the correct MT each from opposite pole

3. positioning chromosomes at the equator

How is the first problem of metaphase organization fized (attatch kinetochore)

rapid MT growth allows for increased likelihood that kinetochore attaches to the + end of the MT. This decreases the frequency of catastrophe making the attachement more persistat

what is chromosome congression

aligning the chromosomes on the metaphase plate

what is bi-orientation

when each sister chromatid’s kinetochore is attatched to a MT from opposite ends

How is problem 3 of preparing metaphase solved (chromosome congression)

describe from moving chromosome left to right towards middle

1. Kinesin-13 is used to shorten the MT (depolymerization) and Dynein complex moves chromosome along the - end —> right chromatid moving right

2. Kinesin-7 on the other end holds onto the kinetochore as the MT + end grows —> left chromatid is moving right

3. Tethered dynactin-dynein complex on the right kinetocore isnt pulling yet but just tethered (will pull later…)

4. Kinesin-4 + end directed motor interacts with polar and knetochore MTs pull chromosomes toward the center of the spindle away from the poles

what happens when congression is complete

dynein/dynactin is released from the kinetochores and moves down the kinetochore MTs to - ends of the MT and towards spindle poles

How does the cell know when it is ready for anaphse (2)

1. mechanism to ensure that each chromosome is properly bioriented (one MT from each end)

2. mechanism to ensure that all of the chromosomes are properly bioriented

What is the mechanism to ensure that each chromosome is properly bioriented (one MT from each end)

bi-oriented chromosomes are under tension

explain what happens when there is no tension —> chromosome not attatched to both poles

Ndc80 and Aurora B stay close together which allows Aurora to phosphorylate Ndc80. Ndc80-P causes looser attatchement to MT

where are Ndc80 and Aurora B

Ndc80 —> outer kinetochore

Aurora B —> Chromosome passenger complex (CPC) on iner kinetochore

What happens when there is tension

Ndc80 stretches which increases space between it and the inner kinetochore. Leads to loss of Aurora B phos so there is tighter kinetochore-MT interactions

What does PP1 do

localizes to outer kinetochore and de-phos Ndc80 when there is tension

What is the mechanism to ensure that all of the chromosomes are properly bioriented

The spindle assembly checkpoint which stops the progression of the cell cycle into anaphase until all chromosmes are under tension

What are the two major events of Anaphase (2)

1. cleaving of cohesins

2. sister chromatid separation

what is a cohesin

ring-shaped protein complex that acts as molecular glue to hold sister chromatids