Pharmacodynamics: Receptors Overview
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Questions and Answers

What is the primary function of receptors in pharmacodynamics?

  • To transport drugs across the cell membrane.
  • To block all extracellular signals.
  • To initiate effects when a ligand binds. (correct)
  • To degrade neurotransmitters in the synapse.

What characterizes ligand-gated ion channels?

  • They have slow and prolonged responses.
  • They are inactive regardless of ligand presence.
  • They generate action potentials rapidly when activated. (correct)
  • They remain open at all times.

Which type of receptor is coupled to a G protein?

  • Voltage-gated ion channel.
  • Nuclear receptor.
  • G-protein coupled receptor (GPCR). (correct)
  • Enzyme-linked receptor.

What determines the effect of a drug on its target receptor?

<p>The affinity and intrinsic activity of the drug. (C)</p> Signup and view all the answers

What describes a characteristic of lipid-soluble ligands?

<p>They interact with intracellular receptors after diffusion. (A)</p> Signup and view all the answers

In the key & lock model of receptor-ligand interaction, what does the 'key' represent?

<p>The drug. (C)</p> Signup and view all the answers

What is the duration of the response when a ligand binds to a ligand-gated ion channel?

<p>Only a few milliseconds. (A)</p> Signup and view all the answers

Which type of receptor will typically lead to a slower response compared to others?

<p>Nuclear receptor. (B)</p> Signup and view all the answers

What mechanism causes the influx of Na+ and Ca2+ ions when a ligand binds to a receptor?

<p>Ligand-gated ion channel (A)</p> Signup and view all the answers

Which type of ion channel opens due to physical distortion of the cell membrane?

<p>Mechanically-gated ion channel (D)</p> Signup and view all the answers

Which ion has a significantly higher concentration outside the cell compared to inside?

<p>Na+ (C)</p> Signup and view all the answers

What kind of receptor is characterized by having 7 transmembrane helices?

<p>G Protein-Coupled Receptor (GPCR) (C)</p> Signup and view all the answers

Which subunit of the G protein binds to guanosine diphosphate?

<p>α subunit (C)</p> Signup and view all the answers

Which type of ion channel opens and closes randomly without external stimuli?

<p>Leakage ion channel (A)</p> Signup and view all the answers

Which second messenger pathway is stimulated by Gs subtype of G protein?

<p>Stimulation of Adenylyl Cyclase (B)</p> Signup and view all the answers

What characteristic action do second messengers have in relation to GPCR signals?

<p>Amplify and conduct signals (A)</p> Signup and view all the answers

What is the primary role of G protein-coupled receptors (GPCR) upon ligand binding?

<p>They activate G proteins, leading to the replacement of GDP with GTP. (B)</p> Signup and view all the answers

Which second messengers are produced through the activation of phospholipase C (PLC)?

<p>IP3 and DAG (B)</p> Signup and view all the answers

What cellular response duration is typically associated with enzyme-linked receptors?

<p>Minutes to hours (D)</p> Signup and view all the answers

Which of the following correctly describes the activation process of G proteins?

<p>GTP binds to the α subunit, causing dissociation. (D)</p> Signup and view all the answers

What is the mechanism of the insulin receptor after ligand binding?

<p>It phosphorylates tyrosine residues to increase enzyme activity. (C)</p> Signup and view all the answers

What function does diacylglycerol (DAG) serve in the cellular signaling pathway?

<p>It acts as a second messenger to activate protein kinase C. (B)</p> Signup and view all the answers

In which part of the cell are intracellular receptors typically located?

<p>Cytoplasm or nucleus (A)</p> Signup and view all the answers

Which of the following is a characteristic of responses mediated by G protein-coupled receptors?

<p>Responses are typically short-lived, lasting seconds to minutes. (A)</p> Signup and view all the answers

What is the primary role of transcription factors in relation to ligand-receptor complexes?

<p>To translocate to the nucleus and induce transcription (A)</p> Signup and view all the answers

Which of the following describes the action of Tamoxifen in breast cancer treatment?

<p>It binds to estrogen receptors, acting as an antagonist (A)</p> Signup and view all the answers

What is a characteristic feature of tachyphylaxis?

<p>It can occur rapidly, sometimes with the initial dose (C)</p> Signup and view all the answers

What happens to receptors during receptor-mediated desensitization?

<p>Receptors may change conformation or be internalized (B)</p> Signup and view all the answers

Which mechanism does not involve receptor-mediated changes?

<p>Reduction in signaling molecules (D)</p> Signup and view all the answers

What potential outcome can occur due to receptor down-regulation?

<p>Restoration of sensitivity via surface recycling (B)</p> Signup and view all the answers

Which of the following roles does the ligand play in cellular signaling?

<p>It must have high lipid solubility to diffuse across membranes (C)</p> Signup and view all the answers

What is a potential consequence of repeated drug administration?

<p>Changes in receptor responsiveness over time (A)</p> Signup and view all the answers

Flashcards

Leakage Ion Channel

A type of ion channel that opens and closes randomly, contributing to the resting membrane potential.

Mechanically-gated Ion Channel

A type of ion channel that opens in response to a physical distortion of the cell membrane, such as pressure or temperature changes.

Ligand-gated Ion Channel

A type of ion channel that opens in response to the binding of a specific ligand molecule.

G Protein-Coupled Receptor (GPCR)

A type of transmembrane receptor that activates intracellular signaling pathways through the interaction of a G protein.

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Second Messengers

Small molecules that amplify and relay signals within a cell, often activated by GPCRs.

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Cyclic AMP (cAMP)

A second messenger that activates a cascade of enzymatic reactions, ultimately leading to changes in gene expression or other cellular processes.

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Gs Protein

A G protein subtype that stimulates adenylyl cyclase, leading to increased cAMP levels.

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Gi Protein

A G protein subtype that inhibits adenylyl cyclase, leading to decreased cAMP levels.

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Receptors

Cellular macromolecules that bind to ligands to initiate effects. They act as key to unlock a response via 'lock and key model'.

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G-protein Coupled Receptors (GPCRs)

Receptors that activate G proteins to trigger a cascade of intracellular events.

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Enzyme-Linked Receptors

Receptors that bind to ligands and activate enzyme activity, initiating intracellular signaling.

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Intracellular Receptors

Receptors that reside inside the cell and bind to lipid-soluble ligands that can cross the cell membrane.

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Affinity

The tendency of a drug to bind to its specific receptor.

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Intrinsic Activity

The ability of a drug to activate a response after binding to a receptor.

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Down-regulation of Receptors

A process where the number of receptors in a cell decreases, leading to a reduced response to a drug.

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Agonist

A drug molecule that binds to a receptor and activates it, mimicking the effects of the natural ligand.

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Antagonist

A drug molecule that binds to a receptor but does not activate it, blocking the effects of the natural ligand.

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Tachyphylaxis

A type of drug desensitization that occurs rapidly, often within the first dose.

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Receptor-mediated desensitization

A mechanism of drug desensitization where the receptor itself is altered, leading to reduced responsiveness.

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Reduction in receptor number

A mechanism of drug desensitization where the number of receptors is reduced, leading to decreased sensitivity.

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Estrogen receptor (ERα)

A specific receptor located in the cytoplasm that binds to estrogen, playing a role in cell proliferation and breast cancer development.

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Tamoxifen

An anti-cancer drug that acts as an antagonist of the estrogen receptor, inhibiting the growth of breast cancer cells by blocking estrogen's effects.

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G-protein Coupled Receptor Signaling

A type of cell signaling pathway where messenger molecules bind to and activate G protein-coupled receptors (GPCRs), triggering a cascade of events that ultimately lead to a cellular response.

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Adenylyl Cyclase

An enzyme that converts ATP into cAMP, a key second messenger in signaling pathways. It's activated by Gs proteins.

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Ligand Activation of G Protein-Coupled Receptors

The process of a ligand binding to a receptor, activating a G protein, and triggering a cascade of events that lead to a cellular response. This is the initiation step in GPCR signaling.

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Phosphoinositide Pathway (IP3/DAG) Pathway

A type of cell signaling pathway that involves the activation of phospholipase C (PLC) by a G protein, leading to the production of second messengers, IP3 and DAG. This pathway plays a crucial role in calcium signaling and other cellular processes.

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Study Notes

Pharmacodynamics: Receptors

  • Receptors are cellular macromolecules that a ligand binds to initiate its effects
  • Drugs bind and transduce extracellular signals to intracellular responses
  • Receptors have specific binding sites for ligands (key & lock model)
  • Drug effectiveness depends on two factors: affinity and intrinsic activity
    • Affinity is the tendency to bind to the receptor to form a drug-receptor complex
    • Intrinsic activity is the ability to trigger a response after forming a drug-receptor complex

Types of Receptors

  • Ligand-gated ion channels
    • Examples: cholinergic nicotinic receptors
  • G protein-coupled receptors (GPCRs)
    • Examples: alpha and beta adrenoceptors, insulin receptors
  • Enzyme-linked receptors
    • Examples: epidermal growth factor (EGF) receptors, insulin receptors
  • Intracellular receptors
    • Examples: steroid receptors

Major Receptor Types

  • Ligands are generally hydrophilic or hydrophobic (lipophilic)
  • Ligand-gated ion channels
    • Located on cell membranes
    • Open when activated by an agonist
    • Rapid response (milliseconds)
    • Examples: Nicotinic acetylcholine receptors
  • Mechanically-gated ion channels
    • Open in response to physical distortion of the cell membrane
    • Examples: skin pressure/temperature changes
  • Leakage ion channels
    • Open and close randomly
    • Contribute to the resting transmembrane voltage

G Protein-Coupled Receptors (GPCRs)

  • Composed of 7 transmembrane helices
  • Ligand-binding site is extracellular
  • Intracellular domain is linked to a G protein
  • G protein has three subunits: a, β, and γ
  • GPCRs have different variants with different functions
    • Examples: stimulate adenylyl cyclase or phospholipase C activity
  • Second messengers (like cAMP) are essential for signal amplification

Enzyme-Linked Receptors

  • Consist of proteins that can form dimers or multi-subunit complexes
  • Ligand binding causes conformational change and increases cytosolic enzyme activity
  • Specific proteins are phosphorylated
  • Duration of responses is minutes to hours
  • Examples: Epidermal growth factor (EGF) receptor, insulin receptor

Intracellular Receptors

  • Receptors are entirely intracellular
  • Ligands must be highly lipid-soluble to diffuse across the membrane
  • Primary drug targets are transcription factors
  • Activated ligand-receptor complexes translocate to the nucleus and bind to specific DNA sequences
  • Influencing transcription and translation
  • Duration of responses is hours to days

Comparison of Receptor Types

  • Receptor types differ in activation mechanisms and duration of response

Desensitization and Down-Regulation of Receptors

  • Repeated administration of a drug(agonist or antagonist) can change receptor responsiveness

  • Tachyphylaxis: rapid desensitization, sometimes occurring with the initial dose

  • Desensitization mechanisms:

    • Receptor-mediated
      • Change in receptor conformation
      • Example: phosphorylation of specific amino acids (aas) blocks coupling of G proteins
    • Non-receptor-mediated
      • Decrease in signaling components (e.g., depletion of second messengers)
      • Increase in metabolic degradation (e.g., increased metabolism or elimination)

  • Down regulation: decreased number of receptors (internalization into the cell)

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Related Documents

3.1 Receptors PDF - MAHSA University

Description

Explore the fundamental concepts of pharmacodynamics, focusing on receptors and their interaction with ligands. This quiz covers various types of receptors, including GPCRs and ligand-gated ion channels, as well as key factors such as affinity and intrinsic activity. Test your knowledge on how drugs communicate signals within cells.

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