Chapter 9.3, Problem 4MI

Summary Introduction

To fill:

Correct words from the given list to complete the given paragraph.

Introduction:

Cells reproduce by a cycle of growing and dividing called the cell cycle. There are three main stages of a cell cycle; interphase, mitosis and cytokinesis. A cell cycle has built in checkpoints that monitor the cycle and can stop the cycle if something goes wrong. There are three checkpoints; G₁, G₂ and M to control the speed at which a cell moves through a cell cycle.

Answer to Problem 4MI

Cells use cyclins and cyclin- dependent kinases to control the cell cycle. Different combinations of cyclin/ CDK start the cycle at different checkpoints. The cell also uses cyclin/ CDK to monitor the cycle for quality control. In G₁stage, the cell checks the DNA for damage. If there is any damage, the cycle won’t proceed to S stage. In mitosis, if the spindle apparatus is malfunctioning, the cycle won’t proceed to cytokinesis.

Explanation of Solution

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. They also check the cycle for quality control. There are three checkpoints; G₁, G₂ and M to control the speed at which a cell moves through a cell cycle. A cell spends most of the time in interphase. It is the stage in which a cell grows, carries out cellular activities and replicates. It makes copies of DNA to enter the next stage of the cycle. During interphase a cell does not divide but prepares itself for cell division. There are three stages in interphase; G₁, S and G₂. In G₁ stage, cell grows, carries out regular cell functions and prepares for synthesis of DNA. The G₁ checkpoint checks for any damage in DNA. If everything is right then only the cell proceeds to next stage. In S stage DNA is replicated and in G₂stage cell prepares for cell division.

The next stage is mitosis in which cell’s nucleus and nuclear material divides. If there is any problem with the spindle apparatus during this stage, the cell would not move to next stage of cytokinesis.