8. Please describe how the cytoskeleton plays a role in chromosome segregation d

Question

8. Please describe how the cytoskeleton plays a role in chromosome segregation during mitosis.

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B. Please describe how the cytoskeleton plays a role in cytokinesis.

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C. You have found an unlabeled bottle which you believe contains either nocodazole (a drug which inhibits microtubule polymerization) or cytochalasin D (a drug which destabilizes actin filaments). To identify which drug it is, you add an aliquot to a culture of cells. You find that under treatment with this drug, cells are able to undergo mitosis, but a binucleate cell (a cell containing two nuclei) is generated. Which drug is in the bottle? Please provide a reason for your prediction.

Explanation / Answer

Ques-8: In prokaryotes, there are presence of cytoskeleton, in which, actin filaments and microtubule filaments are going to maintain cell rigidity at the time of chromosome segregation during mitosis. .

Microtubules are the main cytoskeletal filaments, which are going to promote the growth of spindle fiber during formation of metaplate of cell division & during chromosome segregation during mitosis.. Therefore, kinetochore is going to microtubules through plus ends & minus ends. Minus ends are going to shrink due to a dyenin whereas microtubules toward plus ends with growing due to kinesin protein as a result axoplasmic movement occurs for “mediate Golgi-vesicular movement inside the cell and across cell membrane. However, if at plus end catastrophin binding proteins are going to bind to initiate dynamic instability of the microtubules result in GTP hydrolysis at the plus ends

Abp (actin binding protein) is an actin nucleating protein that do not binds to the “minus end of actin” but binds to the “plus end” (example proflin) and is responsible for web like actin structures involved with “cell axoplasmic movement” such as Arp2/3. Cofflin is the actin binding protein mainly involved in assembly & disassembly of actin through “sequestration” within inactive ADP-bound form finally avoid their reincorporation into actin filaments.

WASP protein family increases actin polymerization at faster rate by promoting activity of Arp2/3 complex using CR1B protein domain. Therefore, both Arp2/3 alone acts on actin polymerization result in low rate but in the presence of WASP family proteins, polymerization rate is higher. In case, in the absence of Arp2/3 or WASP proteins, the actin polymerization is low.

QUes-b:

An epithelial cell grown in culture arranges its microtubule cytoskeleton in terms of polarity because these epithelial cells often not anchored to centrosomes so that they are stabilized by "calmodulin-regulated spectrin-associated protein 3" specifically at non-centrosomal sites. These proteins are going to determine cell polarity. The cell should organize their polarity to deliver efficient cell division including both karyokinesis (nuclear division) with equal chromosomal distribution followed by cytokinesis (cytoplasmic division)

Mechanism:

Microtubules are made of single tubulin protein and it has a dimer i.e. alpha-tubulin & beta-tubulin. These microtubules are going to grow unequally in which, plus end is going to grow faster whereas minus end is going to grow slower. The alpha- tubulin and -tubulin are going to bind with GTP to promote polymerization. During anaphase, polar microtubules with free concentration of free tubulin subunits are found at the poles due to pulling force generated by microtubules on the chromosomes.

GTP (Guanosine triphosphate) into GDP upon hydrolysis, Beta-tubulin, MAPs (microtubule-associated protein)

1. Microtubule GTP cap: Microtubules are polar bodies in which T form is considered as heterodimer. They are possessing both tubulin and associated tubulin

2. These both tubulin molecules have the capability to bind to the GTP and enable the stability of the positive (+) end this end is considered as faster growing end. This can be done by the GTP hydrolysis.

3. T form heterodimer is the ability to bind to the positive (+) end by GTP hydrolysis into GDP form finally become acquire D from. Microtubules GTP cap (+) end has the ability to grow faster and shrink at Polar Regions depending on availability of GTP.

Ques-c:

Nocodazole ---> a drug which inhibits microtubule polymerization

Cytochalasin D ---> a drug which destabilizes actin filaments

An aliquot to a culture of cells are taken. The cells are able to undergo mitosis, but a binucleate cell (a cell containing two nuclei) is generated so that cells failed to perform "karyokinesis" due to inhibition of microtubule polymerization

Reason: Normally, microtubules are made of single tubulin protein and it has a dimer i.e. alpha-tubulin & beta-tubulin. These microtubules are going to grow unequally in which, plus end is going to grow faster whereas minus end is going to grow slower. The alpha- tubulin and -tubulin are going to bind with GTP to promote polymerization. During anaphase, polar microtubules with free concentration of free tubulin subunits are found at the poles due to pulling force generated by microtubules on the chromosomes. This polymerization step inhibited by nocodazole (a drug which inhibits microtubule polymerization) finally causes no karyokinesis

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