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 __________.

G-protein-coupled receptors __________, whereas receptor tyrosine kinases __________.

Which of the following is activated when the binding of single molecules causes it to form a dimer?

Domoic acid is a neurotoxin produced by some species of alga. Domoic acid binds to the kainate receptor on neurons in parts of the brain. The kainate receptor facilitates the movement of calcium into the cell. Excess domoic acid–induced stimulation of the neural kainate receptors causes neural damage and short-term memory loss. Based on this, which of the following is likely true?

A G protein is active when __________.

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?

Cholera develops when the bacterial toxin __________.

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.