Chapter 9, Problem 31A

Summary Introduction

Introduction:

The timing and rate of cell division are very important to the well- being of an organism. The rate of cell division varies depending on the type of cell. There is mechanism involving proteins and enzymes that control the cell cycle. A combination of these two substances is required to signal the cellular reproduction processes.

Answer to Problem 31A

Correct answer :

The correct answer is option B. to signal for the cell to divide

Explanation of Solution

Explanation/justification for the correct answer:

Option B. to signal for the cell to divide−Cell cycle is controlled by a mechanism involving certain proteins and enzymes. Proteins called cyclins bind to enzymes called cyclin- dependent kinases (CDK) during the stages of interphase and mitosis to signal the cell to start the process of cell cycle. Different cyclin and CDK combinations control different activities at different stages of cell cycle.

Hence this is the correct option.

Explanation for incorrect answer:

Option A. to control the movement of microtubules−The movement of microtubules during the mitosis is controlled by certain motor proteins and not cyclins. Hence this is not the correct option.

Option C. to stimulate the breakdown of the nuclear membrane- The breakdown of the nuclear membraneduring prophase stage of mitosis is not controlled by cyclins. Hence this is not the correct option.

Option D. to cause the nucleolus to disappear- During prophase the nucleolus disappears. This is not controlled by cyclins. Hence this is not the correct option.