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In most cells, where do all microtubules originate? What is the difference between a kinetochore and...

  1. In most cells, where do all microtubules originate?
  1. What is the difference between a kinetochore and a centromere?
  1. During mitosis, the breakdown of the nuclear envelope depends on the:

a. disassembly following proteasomal degradation of intermediate filaments.

b. disassembly of lamin filaments following phosphorylation by mitotic cyclin/cdk complexes.

c. ubiquitination of mitotic cyclin proteins.

d. lamin filament dephosphorylation by cdc14.

  1. Which of the following occurs during anaphase A?

a. The spindle elongates.

b. Kinetochores remain attached to shortening kinetochore microtubules.

c. Chromosomes move to the spindle equator.

d. The spindle poles move closer together.

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Answer #1

1) A centromere is the tightly packed specialized region of DNA which is the point of attachment for two sister chromatids. It is made up of tightly wound DNA

The kinetochore is a multi-unit protein complex which attaches to the centromere and then this kinetochore attaches to the mitotic spindle which pull the sister chromatid apart during mitotic division.

2) The nuclear envelope contains a meshwork of laminin and this laminin after dephosphorylation by cyclin dependent kinase 2 turns into individual laminin dimers.

Hence the only answer is option B showing disassembly of lamin fibers by mitotic cyclin cdk complexes.

3 In anaphase A the mitotic spindle pulls the daughter chromosomes to the opposite end of the spindle by shortening of the microtubules attached to the kinetochore. The kinetochore stays attached to the mitotic spindle. Hence the answer is

Option B) The kinetochores remain attached to shortening kinetochore microtubules.

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