The eukaryotic cell cycle is under both external and internal control. Cdk’s control the eukaryotic cell cycle, and their activities are regulated by binding of cyclins. External signals such as growth factors can initiate the cell cycle.
learning outcomes
You should be able to:
Identify each phase of the cell cycle using diagrams or descriptions.
Explain how the progress of a eukaryotic cell through the cell cycle is controlled.
Describe the ways in which progress through the cell cycle is modulated.
Predict the effects of external factors on the eukaryotic cell cycle.
Draw a cell cycle diagram and describe the three subphases of interphase.
See Figure 11.3.
How do cyclin–
The Cdk’s are made throughout the cell cycle. However, their protein kinase active site is not available for target substrates for cell cycle activities unless a particular cyclin molecule binds to the Cdk. It is the cyclins that are made, bind to Cdk’s to activate, and then break down. The transient nature of the cyclins controls each Cdk activation in sequence at the cell cycle control points.
What are growth factors, and how do they act to control the cell cycle?
Growth factors are proteins made by cells that can travel to other cells, or act on the cells that make them, usually to stimulate cell division. Growth factors bind to specific receptors on target cells, setting off signal transduction inside the cells. This can lead to gene expression for cyclins, for example, and the cell cycle is stimulated.
The protein p16 acts on the cell cycle in a fashion similar to that of p21. Recently it was found that there is more p16 protein in the cells of older people than in younger people. What are the implications of this for aging?
P16 blocks the interaction of cyclin and its Cdk that act at the G1–
Once the cell cycle is initiated and interphase completed, the cell enters mitosis, where the replicated DNA is segregated into two daughter cells.