The molecule cAMP usually directly activates __________.

Kinases and phosphatases are essential to the cell because they:

a) Are enzymes that synthesize proteins.

b) Are enzymes that degrade proteins.

c) Are enzymes that can turn proteins 'on' and/or 'off' through changes in phosphorylation.

d) Are enzymes that can turn proteins 'on' and/or 'off' through changes in proton concentrations.

e) None of the above.

What role do phosphatases play in signal transduction pathways?

a) They phosphorylate proteins involved in signal transduction or cellular response.

b) They activate protein kinases by phosphorylation.

c) They amplify the signal molecule.

d) They regulate the function of proteins involved in signal transduction pathways or cellular response.

Phosphorylation cascades are useful signal transduction pathways because they ________.

a) Allow proteins to be easily activated by adding or removing a phosphate group.

b) Allow proteins to be easily deactivated by adding or removing a phosphate group.

c) Amplify the original signal many times.

d) All of the above.