Ch. 11 - Cell Communication

Problem 4

Chapter 11, Problem 4

Consider this pathway: epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP. Identify the second messenger. a. cAMP b. G protein c. GTP d. adenylyl cyclase

Verified step by step guidance

Step 1: Understand the concept of a second messenger. A second messenger is a molecule that relays signals received at receptors on the cell surface to target molecules inside the cell. They are part of the process of signal transduction in cells.

Step 2: Look at the given pathway: epinephrine → G protein-coupled receptor → G protein → adenylyl cyclase → cAMP. The signal starts with epinephrine and ends with cAMP.

Step 3: Identify the molecules that are inside the cell. In this case, G protein, adenylyl cyclase, and cAMP are inside the cell.

Step 4: Determine which of these molecules is the second messenger. The second messenger is the molecule that transmits the signal from the receptor to other parts of the cell. In this pathway, the second messenger is cAMP.

Step 5: Therefore, the answer is a. cAMP.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Second Messengers

Second messengers are intracellular signaling molecules released by the cell in response to exposure to extracellular signaling molecules (first messengers). They play a crucial role in amplifying the signal and facilitating communication within the cell. Common examples include cyclic AMP (cAMP) and calcium ions, which help propagate the effects of hormones and neurotransmitters.

G Protein-Coupled Receptors (GPCRs)

G protein-coupled receptors are a large family of membrane receptors that detect molecules outside the cell and activate internal signal transduction pathways. When a ligand, such as epinephrine, binds to a GPCR, it causes a conformational change that activates an associated G protein, which then influences various downstream effectors, including enzymes like adenylyl cyclase.

Adenylyl Cyclase and cAMP

Adenylyl cyclase is an enzyme that converts ATP to cyclic AMP (cAMP), a key second messenger in many signaling pathways. The production of cAMP is often triggered by the activation of GPCRs and is crucial for mediating the effects of hormones like epinephrine. cAMP then activates protein kinase A (PKA), leading to various cellular responses.

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Related Practice

Textbook Question

Binding of a signaling molecule to which type of receptor leads directly to a change in the distribution of substances on opposite sides of the membrane? a. intracellular receptor b. G protein-coupled receptor c. phosphorylated receptor tyrosine kinase dimer d. ligand-gated ion channel

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Textbook Question

The activation of receptor tyrosine kinases is characterized by a. dimerization and phosphorylation. b. dimerization and IP3 binding. c. a phosphorylation cascade. d. GTP hydrolysis.

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Textbook Question

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.

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Textbook Question

Apoptosis involves all but which of the following? a. fragmentation of the DNA b. cell-signaling pathways c. lysis of the cell d. digestion of cellular contents by scavenger cells

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Textbook Question

Which observation suggested to Sutherland the involvement of a second messenger in epinephrine's effect on liver cells? a. Enzymatic activity was proportional to the amount of calcium added to a cell-free extract. b. Receptor studies indicated that epinephrine was a ligand. c. Glycogen breakdown was observed only when epinephrine was administered to intact cells. d. Glycogen breakdown was observed only when epinephrine and glycogen phosphorylase were mixed.

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Open Question

Protein phosphorylation is commonly involved with which of the following?

A. ligand binding by receptor tyrosine kinases.

B. activation of G protein-coupled receptors.

C. activation of protein kinase molecules.

D. release of Ca2+ from the ER lumen.

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