10. Cell Signaling

The molecules that convert extracellular signals into intracellular signals are:

Which type of receptor leads directly to a change in the distribution of ions on opposite sides of the membrane?

Why does testosterone, a lipid-soluble / hydrophobic signaling molecule, not affect all cells in the body but only specific cells?

Lipid-soluble signaling molecules, such as aldosterone, cross the membranes of all cells but affect only target cells because

a. 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.