Cholera develops when the bacterial toxin __________.

A G protein is active when __________.

If a modified form of GTP that cannot be enzymatically converted to GDP were added to a culture of cells, the likely result would be __________.

What event would activate a G protein?

Ras, a small G protein located at the plasma membrane, is often mutated in different types of cancer. Ras normally signals to a cell that it should divide. Cancer cells divide uncontrollably. Which of the following changes to Ras could explain uncontrolled division in a cancer cell that has mutated Ras present?

Lipid-soluble signaling molecules, such as aldosterone, cross the membranes of all cells but affect only target cells becausea. only target cells retain the appropriate DNA segments.b. intracellular receptors are present only in target cells.c. only target cells have enzymes that break down aldosterone.d. only in target cells is aldosterone able to initiate the phosphorylation cascade that turns genes on.

Summarize the experimental evidence in sponges showing that animal cells adhere to each other selectively. Explain the molecular basis of selective adhesion.

Suppose you have an antibody that binds to the receptor tyrosine kinase illustrated in Figure 11.16. When you add this antibody to the cell, you find that it activates the cell response, even when no signaling molecule is present. Explain this result.