8.2.1 Cell-Cycle Regulation: Protein Kinases

Question 1

checkpoints

Answer 1

• serve as regulation points where a cell will either proceed into the cell cycle or remain in its current phase
• The three main checkpoints in the cell cycle are named after where they take place. They are G1, G2, and M.

Question 2

protein kinases

Answer 2

• molecules that transfer phosphate groups from molecules like ATP and GTP to other molecules. Often
  kinases are inactive unless an activator protein is present
• A particular class of protein kinases, called cyclin-dependent kinases (Cdk), allow the cell to proceed through a checkpoint.

Question 3

Cyclin-dependent kinases (Cdk)

Answer 3

• a particular group of enzymes involved in cell cycle regulation. When the protein cyclin binds to a Cdk, it is activated. The activated form is called MPF (standing for maturation promoting factor).

Question 4

note

Answer 4

• Notice on the graph that as cyclin increases MPF activity (curved line) eventually follows and the cell enters mitosis. As cyclin accumulates, more MPF is formed.
• MPF brings the cell into mitosis from the G2 checkpoint by phosphorylating the nuclear lamina, which causes the nuclear envelope to break down. (Remember: The nuclear envelope breaks down during prometaphase.)
• MPF inactivates itself by initiating the digestion of cyclins.As cyclin levels go down, MPF levels also go down. Cdk levels remain relatively constant in the cell.

Question 5

Which statement regarding protein kinases is true?

Answer 5

• Cyclin binds to Cdk to make MPF, an active protein kinase

Question 6

The MPF concentration declines at the end of the cell cycle. This decrease is caused by:

Answer 6

• the destruction of cyclin by proteolytic enzymes

Question 7

True or false?

An enzyme that transfers a phosphate group is a kinase.

Answer 7

• true

Question 8

Which of the following best describes the role of a checkpoint?

Answer 8

• A checkpoint is the period of time during which the cell cycle stops until otherwise signaled

Question 9

The progression of cells through the cell cycle is regulated by the concentration of which of the following?

Answer 9

• cyclins

Question 10

During which of the following phases is Cdk present in the cell?

Answer 10

• G1
• S
• G2
• all of the above

Question 11

Cyclin levels peak during which phase of the cell cycle?

Answer 11

• M