G Protein-Coupled Receptors and Signaling

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Questions and Answers

What role does adenylyl cyclase play in cellular signaling?

It regulates gene expression directly.

It fragments proteins for degradation.

It transmits signals through ion channels.

It converts ATP to cyclic AMP. (correct)

How does cyclic AMP (cAMP) contribute to cellular responses?

By phosphorylating lipids in the cell membrane.

By inhibiting G protein activation.

By directly altering the cell's membrane potential.

By activating protein kinase A, which then phosphorylates other proteins. (correct)

Which of the following statements best describes the function of protein kinase A in the signaling pathway?

It phosphorylates proteins to elicit a cellular response. (correct)

It initiates the formation of G proteins.

It directly stimulates adenylyl cyclase activity.

It acts as a second messenger itself.

What is the primary function of GPCRs in cellular signaling?

To amplify the signal through second messengers. Signup and view all the answers

What mechanism ensures signal amplification in the pathway involving cyclic AMP?

Each adenylyl cyclase can produce multiple molecules of cAMP. Signup and view all the answers

What characteristic of receptors allows them to be activated by varying ligand concentrations?

Saturable Signup and view all the answers

Which of the following is the primary function of adenylyl cyclase in hormone signaling?

Converts ATP to cAMP Signup and view all the answers

How does cyclic AMP (cAMP) function as a second messenger in cellular signaling?

Activates protein kinases Signup and view all the answers

What is the role of Protein Kinase A (PKA) in response to cAMP?

Phosphorylates specific protein targets Signup and view all the answers

Which scenario best demonstrates signal amplification in cells?

One activated adenylyl cyclase generates multiple cAMP molecules. Signup and view all the answers

Which characteristic of intracellular receptors allows them to respond to hydrophobic hormones?

Ability to bind ligands in the cytoplasm or nucleus Signup and view all the answers

What happens when there is a saturation of receptors by a hormone in the cell?

Additional hormone has no effect on signaling. Signup and view all the answers

What distinguishes hormonal signaling from neural signaling?

Hormones have specific target cells that respond to them. Signup and view all the answers

What connects the cytoplasmic tail of G protein-coupled receptors (GPCRs) to the G protein?

Membrane-spanning proteins Signup and view all the answers

Which of the following is a role of G proteins when activated?

Activate enzyme activity on the cytoplasmic side of the membrane Signup and view all the answers

What is the primary role of adenylyl cyclase in the signal transduction pathway?

Catalyze the formation of cAMP from ATP Signup and view all the answers

How does cAMP function as a second messenger in the signaling pathway?

By activating protein kinase A Signup and view all the answers

Which component is essential for the amplification of the signal in the GPCR-adenylyl cyclase pathway?

The conversion of ATP to cAMP Signup and view all the answers

What happens to protein kinase A after it is activated by cAMP?

It phosphorylates target proteins, leading to a cellular response Signup and view all the answers

What is a key characteristic of G protein-coupled receptors (GPCRs) in terms of their structure?

They are comprised of multiple transmembrane segments Signup and view all the answers

Which lipid second messenger is commonly associated with GPCR signaling pathways?

Diacylglycerol (DAG) Signup and view all the answers

Study Notes

G Protein-Coupled Receptors (GPCRs)

Membrane-spanning proteins with a cytoplasmic tail linked to a three-part G protein.
The G protein-coupled adenylyl cyclase-cAMP system is a common signal transduction pathway for many protein hormones.
Utilize lipid second messengers like diacylglycerol (DAG) and inositol trisphosphate (IP3).
Activated G proteins open ion channels in the membrane and alter enzyme activity on the cytoplasmic side.
Gs protein activates adenylyl cyclase.

Adenylyl Cyclase and cAMP Pathway

G protein activation triggers adenylyl cyclase, an amplifier enzyme.
Adenylyl cyclase converts ATP to cyclic AMP (cAMP).
cAMP activates protein kinase A.
Protein kinase A phosphorylates other proteins, leading to a cellular response.
cAMP acts as a second messenger, amplifying the target cell's response.

Hormone Signaling

Hormone binding to a receptor changes the receptor's conformation and activity.
This alters intracellular signaling pathways.
Results in changes in target protein synthesis or modification of existing proteins.

Receptor Characteristics

Receptors are large proteins, often belonging to families.
A single ligand may have multiple receptors, and a single receptor may bind multiple ligands.
The number of receptors per target cell can vary widely (500-100,000).
Receptors can be activated and inhibited.
Locations include the cell membrane, cytoplasm, and nucleus.
Receptors display high affinity, saturability, specificity, and reversibility.

Receptor Saturation

A graph showing the relationship between bound labeled testosterone and total labeled testosterone demonstrates receptor saturation. At a certain point increasing hormone concentration no longer increases the response.

Example of Receptor Saturation

Hormone A binding to receptor B causes response C. Doubling hormone A concentration doubles response C. However, further doubling hormone A has no effect on response C due to receptor saturation

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Description

This quiz covers the fundamental concepts of G Protein-Coupled Receptors (GPCRs), including their structure, the adenylyl cyclase-cAMP signaling pathway, and their role in hormone signaling. Test your knowledge on how these receptors mediate cellular responses through second messengers like cAMP. Dive into the details of G protein activation and the impact on cellular functions.