The schematic diagram to the right shows the activation of M-Cdk in mitosis. Ind

Question

The schematic diagram to the right shows the activation of M-Cdk in mitosis. Indicate what protein (or protein function) corresponds to those indicated as A, B, C, and D in the diagram. Briefly explain the importance of each protein function. Briefly describe how sister chromatids are able to separate during the metaphase-to-anaphase transition. Which one of the chromosomes (A-E) to the right has formed stable attachment(s) to the mitotic spindle? Explain your choice. You have isolated a mutant budding yeast strain that has a slower doubling time (doubling time = 2 hrs) compared to wild-type yeast (doubling time = 1.5 hrs). This leads you to believe the strain may have a mutation in a gene involved in the cell cycle. Describe a technique you could use to confirm this cell cycle defect.

Explanation / Answer

Answer:

1. A: M-Cyclin :

M cyclin promotes the events of M phase, such as nuclear envelope breakdown and chromosome condensation. M cyclin stays at low levels for much of the cell cycle, but builds up as the cell approaches the G2 to M transition. As M cyclin accumulates, it binds to Cdks already present in the cell, forming complexes that are poised to trigger M phase.

B: Cdk-activating kinase (CAK):

The Cyclin-activating kinase (CAK) is responsible for the activating phosphorylation of CDK1, CDK2, CDK4 and CDK6 and regulation of the cell cycle.

C. Cdk-inhibitory kinase (Wee1):

Besides environmental factors such as nutrients, growth factors and functional load, cell size is also controlled by a cellular cell size checkpoint. Wee1 is a component of this checkpoint. It is a kinase determining the timepoint of entry into mitosis, thus influencing the size of the daughter cells.

Wee1 inhibits Cdk1 by phosphorylating it on two different sites, Tyr15 and Thr14. Cdk1 is crucial for the cyclin-dependent passage of the various cell cycle checkpoints. At least three checkpoints exist for which the inhibition of Cdk1 by Wee1 is important:

i. G2/M checkpoint

ii. Cell size check point

iii. DNA damage checkpoint

D. Inactive cdc25 phosphatase:

The Cdc25 family of phosphatases is responsible for dephosphorylating inhibitory Tyr and Thr residues on cyclin-dependent kinases in order to promote their activation. Three isoforms (A, B and C) have been identified in mammals while only two isoforms (A and C) have been characterized in Xenopus.

Traditionally, mammalian Cdc25A was classified as the G1/S-promoting phosphatase, while Cdc25B and Cdc25C were thought to control the G2/M transition. However, more recent evidence suggests that all three isoforms can dephosphorylate Cdc2/Cyclin B and play important roles in the G1/S and G2/M transitions of the cell cycle.

(Since there are more than 1 questions, the first full question have been answered according to the rules of Chegg)

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