- 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.

- 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.

Cyclin-dependent kinases (Cdk)

- 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).

- 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.

Which statement regarding protein kinases is true?

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

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

- the destruction of cyclin by proteolytic enzymes

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

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

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

- G1 - S - G2 - all of the above

8.2.1 Cell-Cycle Regulation: Protein Kinases Flashcards by Irina Soloshenko

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8.2.1 Cell-Cycle Regulation: Protein Kinases Flashcards

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