Pharmacodynamics: Drug-receptors

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Questions and Answers

What is the primary function of ligand-gated ion channels once a ligand binds?

To bind specifically to hydrophilic ligands

To phosphorylate other proteins in the cell

To form a channel that allows ions to flow passively (correct)

To inhibit the flow of ions across the membrane

Which type of receptor typically contains an enzymatic domain that is a protein kinase?

G-protein coupled receptors

Ligand-gated ion channels

Intracellular receptors

Enzyme-coupled receptors (correct)

What triggers the activating change in G-protein coupled receptors once a ligand binds?

The formation of ion channels

A conformational change in the receptor (correct)

The release of tyrosine kinase

The production of GDP

What must happen to the alpha subunit of G proteins for it to become active?

It must release GDP and bind GTP Signup and view all the answers

What characteristic distinguishes G-protein coupled receptors from other types of receptors?

They consist of seven transmembrane segments Signup and view all the answers

Intracellular receptors primarily bind to which type of ligands?

Small and hydrophobic ligands Signup and view all the answers

Enzyme-coupled receptors undergo a conformational change primarily to:

Create high-affinity binding sites for second messengers Signup and view all the answers

Which of the following statements about intracellular receptors is true?

They require a ligand to enter the nucleus. Signup and view all the answers

Which second messenger is activated by DAG?

Protein kinase C Signup and view all the answers

What does the term 'potency' refer to in pharmacology?

The amount of medication needed to elicit an effect Signup and view all the answers

How is efficacy defined among medications?

The maximal effect a medication can produce Signup and view all the answers

What happens at the EC50 point on a dose-response curve?

50% of the maximum effect is reached Signup and view all the answers

In a dose-response curve, what does a curve closer to the left indicate?

Higher potency of the medication Signup and view all the answers

Which of the following G proteins inhibits adenylate cyclase?

Gi Signup and view all the answers

What is the primary function of phospholipase C when activated by Gq proteins?

To cleave PIP2 into IP3 and DAG Signup and view all the answers

Which medication characteristic does not affect affinity?

Concentration of the medication Signup and view all the answers

What shape does a typical dose-response curve take?

S-shaped (sigmoidal) Signup and view all the answers

Between medications C and D, which is described as more efficacious?

Medication C, as it achieves a higher maximal effect Signup and view all the answers

Study Notes

Intracellular Receptors

Located in the cytoplasm or nucleus of cells
Bind to small, hydrophobic ligands, such as steroids
Receptor-ligand complex binds to specific DNA sequences
This interaction activates or inhibits specific genes

Cell-Surface Receptors

Embedded in the plasma membrane
Bind to ligands that are too large or hydrophilic to pass through the membrane
Three main types: ligand-gated ion channels, enzyme-coupled receptors, and G-protein coupled receptors

Ligand-gated Ion Channels (Ionotropic Receptors)

Form channels or pores that are closed in the absence of a ligand
Binding of a ligand opens the channel, allowing ions (chloride, calcium, sodium, potassium) to pass through
Ions flow passively down their concentration gradients
This triggers downstream signaling pathways

Enzyme-coupled Receptors

Usually single-pass transmembrane proteins
Extracellular domain binds to ligands
Intracellular domain has enzymatic activity, typically protein kinase (tyrosine kinase)
Ligand binding triggers conformational changes, creating high-affinity binding sites for second messengers
Tyrosine kinases phosphorylate second messengers, activating other proteins in the signaling pathway

G-protein Coupled Receptors (Seven-Pass Transmembrane Receptors)

Long proteins with one end outside the cell and seven transmembrane segments
Ligand binding on the extracellular end activates guanine nucleotide-binding proteins (G proteins)
G proteins have alpha, beta, and gamma subunits
Alpha subunit binds to GDP in the inactive state
Ligand binding causes the alpha subunit to release GDP and bind GTP
This activation causes the alpha subunit to detach and trigger other proteins in the signaling pathway

Types of G Proteins

Gq, Gi, and Gs
Each type has a unique alpha subunit
Gq activates phospholipase C
Gs and Gi stimulate or inhibit adenylate cyclase, respectively

Second Messengers

IP3, DAG, and cAMP
Produced by the action of G proteins and their target enzymes
IP3 and DAG are produced by phospholipase C
cAMP is produced (or inhibited) by adenylate cyclase
Activate or inhibit various enzymes and molecular pathways

Medication-Receptor Interactions

Three key principles: affinity, potency, and efficacy

Affinity

Strength of the binding interaction between a medication and its receptor
Determined by the chemical bond between the two molecules
Higher affinity generally corresponds to a stronger interaction

Potency

Amount of medication needed to produce a specific effect
High potency requires a lower dose for a given effect
Affinity is directly proportional to potency

Efficacy

Maximum effect a medication can produce
Measured by the Emax (maximum response) on a dose-response curve
Higher efficacy corresponds to a greater maximum response

Dose-Response Curve

Graph showing the relationship between medication concentration (dose) and the response produced
Typically S-shaped (sigmoidal)
X-axis: medication concentration (logarithmic scale)
Y-axis: response

EC50

Median effective concentration
Concentration of medication that produces 50% of the maximum effect (Emax)
EC50 is inversely proportional to potency

Comparing Medications

Higher potency corresponds to a lower EC50 on the dose-response curve (curve shifted left)
Higher efficacy corresponds to a higher Emax on the dose-response curve (curve shifted upward)

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Description

Explore the fascinating world of cell receptors in this quiz, focusing on intracellular receptors and cell-surface receptors. Learn about their structures, functions, and the mechanisms by which they activate or inhibit specific genes and signaling pathways. Test your knowledge on ligand-gated ion channels and enzyme-coupled receptors.