Biology, Eighth Edition (Raven)

Chapter 9: Cell Communication

Mechanism of Action of Lipid-Soluble Messengers

How is the concentration of molecules that can freely pass through cellular membranes controlled inside cells? Many hormones are small, nonpolar molecules that can freely pass through a plasm membrane. Hormones are used in cell signaling and are used to turn specific genes on or off in specific cells. However, if hormones can freely diffuse in and out of cells it would seem to be difficult to build up concentrations in specific parts of the body. If the concentration of a hormone is uniform throughout the body then it has little value as a cellular signal. The answer to this problem is that, once hormones enter target cells, they bind to receptor proteins to from a complex that activates gene expression. Once bound the hormone cannot diffuse back out of the cell and the concentration can increase.

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


The messenger in the lipid soluble messenger system is...

The messenger passes freely through the plasma membrane and...
A)enters the nucleus, where it binds to the DNA molecule.
B)enters the nucleus and binds to the RNA molecule.
C)enters the cytoplasm and binds to a ribosome.
D)attaches to a gated membrane protein.
E)attaches to a protein in the cytoplasm.

The ultimate result of the lipid soluble messenger system is...
A)DNA molecules replicate, and produce a functional response.
B)DNA molecules replicate in preparation for mitosis.
C)the messenger binds with the RNA molecule, which then codes for proteins that produce a functional result.
D)proteins are coded for and synthesized to produce a functional result.
E)transport proteins are incorporated in the cytoplasm of the cell to produce a functional result.

Lipid soluble messengers must bind to a transport protein to be transported by the blood.

Lipid soluble messengers require a transport protein in order to pass through the plasma membrane.
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