chapte 12 pt 2 Cell Signaling Foundations + GPCRs

What is specificity in signal transduction?

Specificity means a ligand binds a receptor that is highly compatible and selective for that ligand.

What does receptor affinity describe?

Affinity describes how strongly a ligand binds to its receptor.

What is the dissociation constant (KD)?

KD is a measurement used to describe ligand-receptor binding affinity.

What does a low KD indicate?

A low KD indicates high affinity between a ligand and its receptor.

What is sensitivity in signal transduction?

Sensitivity is the ability of receptors to detect very small amounts of signaling molecules.

What causes amplification in signaling pathways?

Amplification occurs when activation of one component activates many downstream components.

Why is amplification important?

It allows a small signal to generate a very large cellular response.

What is modularity in signal transduction?

Modularity means signaling proteins contain multiple domains that interact with other proteins.

Why is modularity useful?

It allows cells to mix and match signaling components for different functions.

What is desensitization?

Desensitization is the weakening of a signaling response even when the signal molecule is still present.

What is the purpose of desensitization?

It helps terminate signaling and prevents excessive cellular responses.

What is signal integration?

Signal integration occurs when multiple signaling pathways combine to produce a single response.

Why is signal integration important?

It allows different signals to work together to maintain functions such as homeostasis.

What is response localization?

Response localization focuses signaling in a specific region of the cell.

How do lipid rafts contribute to signaling?

Lipid rafts localize signaling components to specific membrane regions so signals remain concentrated.

Why is response localization important?

It prevents signaling effects from spreading unnecessarily throughout the cell.

What are examples of signaling molecules?

Hormones, neurotransmitters, growth factors, nutrients, glucose, amino acids, and nitric oxide.

Why is nitric oxide an effective signaling molecule?

It is small enough to diffuse across cell membranes.

What are some important protein components of signal transduction pathways?

G proteins, protein kinases, calcium-binding proteins, and membrane receptors.

What are the six major classes of signal transducers discussed in lecture?

G protein-coupled receptors, receptor tyrosine kinases, kinase-linked receptors, gated ion channels, adhesion receptors, and nuclear receptors.

What are the three main classes of membrane receptors discussed in lecture?

Seven-transmembrane receptors, dimeric membrane receptors, and dimeric protein receptors.

What are seven-transmembrane receptors associated with?

Heterotrimeric G proteins.

What are dimeric membrane receptors known for?

They recruit intracellular protein kinases.

What is an example of a dimeric membrane receptor?

Growth hormone receptor.

What is another example of a dimeric membrane receptor?

Erythropoietin (EPO) receptor.

What is an example of a dimeric protein receptor?

Insulin receptor.

What does GPCR stand for?

G protein-coupled receptor.

What type of membrane protein is a GPCR?

An integral membrane protein composed of seven transmembrane alpha helices.

What does GS stand for in GPCR signaling?

G stimulatory.

What are examples of GPCRs?

Beta-adrenergic receptors, opioid receptors, and histamine receptors.

Where are opioid receptors found?

In the brain, peripheral nervous system, spinal cord, and digestive tract.

What functions are regulated by opioid receptors?

Pain, stress, and perception.

What are the three essential components of GPCR signaling?

A receptor, a G protein, and an effector enzyme or ion channel.

What is the inactive state of a G protein?

The alpha, beta, and gamma subunits are associated together and GDP is bound to the alpha subunit.

What nucleotide is bound to inactive G proteins?

GDP.

What causes activation of a G protein?

Replacement of GDP with GTP on the alpha subunit.

What nucleotide is bound to active G proteins?

GTP.

What happens when GTP binds the alpha subunit?

The alpha subunit dissociates from the beta and gamma subunits.

What is the role of adenylyl cyclase?

It is an effector enzyme activated by the G alpha subunit.

What enzyme converts ATP into cAMP?

Adenylyl cyclase.

What is cyclic AMP (cAMP)?

A secondary messenger produced from ATP by adenylyl cyclase.

What is the function of cAMP?

It activates protein kinase A (PKA).

What is a secondary messenger in the epinephrine pathway?

cAMP.

What does protein kinase A do?

It phosphorylates target proteins to produce cellular responses.

What is the structure of protein kinase A?

A heterotetramer composed of two regulatory and two catalytic subunits.

How is protein kinase A activated?

cAMP binds the regulatory subunits, releasing the catalytic subunits.

What happens to the catalytic subunits after activation?

They phosphorylate target proteins.

What happens when cAMP levels fall?

The regulatory and catalytic subunits reassociate, inactivating PKA.