Biology, Eighth Edition (Raven)

Chapter 10: How Cells Divide

How Tumor Suppressor Genes Block Cell Division

What is cancer? Cancer and tumors are the result of uncontrolled cell division. The cell cycle is controlled by regulatory proteins. When the DNA coding for these proteins is damaged then the proteins may not function. One possible outcome of a non-functioning regulatory protein is continuous cell division. A consequence of an uncontrolled cell cycle is that the tissue formed from cell division is often non-functional. Without control the growth does not take on the proper form or interact normally with other cell types.

The root cause of the growth is a genetic defect. Thus, all daughter cells of a cancerous cell will also exhibit the same pattern of uncontrolled growth. Therefore cancers and tumors are very serious diseases.

View the animation below, then complete the quiz to test your knowledge of the concept.


The proteins ________ work together to free the transcription factor that is bound by the retinoblastoma protein.
A)p53 and p21
B)p53 and cyclin
C)cyclin and E2F
D)cyclin and cyclin dependent kinase
E)cyclin dependent kinase and p53

Mutated forms of the Rb protein
A)bind to E2F thereby promoting uncontrolled cell division.
B)bind to E2F thereby inhibiting cell division.
C)bind to E2F but have no effect on cell division.
D)do not bind to E2F thereby inhibiting cell division.
E)do not bind to E2F thereby promoting uncontrolled cell division.

The protein ________ checks for damaged DNA, thereby acting as a "quality control" for the cell.
B)cyclin dependent kinase

The protein p21 keeps cyclin and cyclin dependent kinase from binding to each other.

The protein product of the tumor suppressor gene Rb acts on the G1 checkpoint.
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