A. Please explain what you predict is the effect of a defect in Wee1 and Cdc25 f

Question

A. Please explain what you predict is the effect of a defect in Wee1 and Cdc25 function on the length of the cell cycle.

Wee1 defect -

Cdc25 defect -

B. Why might a change in cell cycle length lead to changes in cell size?

C. Please explain what you predict is the identity of the three strains in the images. Strain 1 - Strain 2 - Strain 3 -

Weel is a protein kinase which inhibits the functions of Cdk's, and its function is opposed by the phosphatase Cdc25. Please explain what you predict is the effect of a defect in Weel and Cdc25 function on the length of the cell cycle. Weel defect - Cdc25 defect - You take images of the cell sizes of three different yeast strains: wild-type, weel defective, and cdc25 defective, which are shown below. Unfortunately, the labels for each image have been lost. (Images originally from Paul Nurse.)

Explanation / Answer

A). Wee1 is a nuclear kinase that belongs to Ser/Thr family, which act as a key regulator of cell cycle progression. It inhibits the entry of cell into mitosis, through inhibiting Cdk1 and thus influences cell size. Loss of function or mutaion in Wee1 protein result in the production of smaller daughter cell than the normal ones because of premature cell division.

Cdc25C promotes the process of entry of cell into mitosis. Mutation in this gene may cause impaired cell division.

b). The change in cell cycle changes cell size because for the completion of all process of cell division , a constant time period is needed, unless incomplete growth occurs, prematute division results.

c). Strain 1 is the normally dividing cells (wild type). Strain 2 are cdc25 defective, cells are not promoted to mitosis, they keep growing without division. Strain 3 are Wee 1 defective, representing premature division.

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