1. A receptor is the third type of protein studied that interacts with small molecules. Distinguish receptors from enzymes and transport proteins that bind solutes by completing the table below. Focus on the majority of cases in answering.

2. The nicotinic acetylcholine (ACh) receptor is an ion channel.
a. Write the steps involved in its activation and response as a sequence.
     You should have 3 steps.
b. How is each effect reversed? Be specific.

3. Summarize the sequence of events that is triggered by epinephrine binding a
β-adrenergic receptor. Note that this is reversible, and that each activation is eventually followed by an inactivation.

4. Classify each molecule in the sequence below by indicating whether it is an enzyme (E), a non-enzyme protein (P), or a non-protein molecule (M).

5. You should have four enzymes listed in Table 3.
a. Write the reaction each enzyme catalyzes.
b. Describe the effect in the G-protein pathway of each product.

6. The G_s protein pathway can be summarized like this:
hormone + receptor → activation of G_sα → activation of AC → cAMP synthesis → activation of PKA → activation of phosphorylase kinase

a. Write a similar sequence for the G_i pathway.
b. Write a similar sequence for the G_q pathway. You will have a branch point for
    this pathway.

7. Amplification occurs any time the molecule on the left of an arrow can have a repeated effect. For example, in the G_s pathway, the receptor can activate several G_s proteins, so amplification occurs at that arrow.
a. At which arrows in the G_s pathway does amplification occur?
b. At which arrows in the G_q pathway does amplification occur?

8. PKA and PKC catalyze similar reactions.
a. Use Table 6-10 in the text and write the consensus sequence recognized by each.
b. Are these sequences more likely to be found on the exterior or interior of a protein?
c. How does the reaction catalyzed by the protein kinase affect protein activity?
d. How is the effect reversed?

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