Biology, Eighth Edition (Raven)

Chapter 9: Cell Communication

Cell Proliferation Signaling Pathway

What keeps the body from growing constantly? The growth of the body depends both on cell division and cell differentiation and specialization. Cells must divide and they must form different kinds of cells to perform different functions. Uncontrolled cell division produces cancerous tissue. The rate of cell division is controlled by molecules known as growth factors as well as by environmental cues. One example of a growth factor is platelet-derived growth factor (PDGF). This growth factor is produced by platelets (a type of blood cell) in the vicinity of a wound. PDGF causes cell division, speeding the healing of the injury.

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


1.	Growth factor receptors are typically found in the

		A)	cell membrane.
		B)	cytoplasm.
		C)	nucleus.
		D)	mitochondria.
		E)	Golgi apparatus.

2.	It the protein retinoblastoma is ________, it can bind to and ________ the Myc protein.

		A)	phosphorylated ; activate
		B)	phosphorylated ; inactivate
		C)	dephosphorylated ; activate
		D)	dephosphorylated ; inactivate
		E)	either B or C

3.	Which of the following statements about the Myc protein is TRUE?

		A)	It binds to DNA.
		B)	It activates the transcription of cyclins and cyclin-dependent kinases.
		C)	It promotes cell division.
		D)	A and B
		E)	A, B and C

4.	Binding of a growth factor to its receptor, usually sets in motion an intracellular cascade of protein phosphorylations.

		A)	True
		B)	False

5.	The dephosphorylated form of retinoblastoma protein promotes cell division.

		A)	True
		B)	False