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What is the term used to describe a naturally occurring small molecule or a drug that binds to a site on a receptor protein and activates it?
What is the term used to describe a naturally occurring small molecule or a drug that binds to a site on a receptor protein and activates it?
What is the characteristic of G proteinlinked and enzyme-linked receptors?
What is the characteristic of G proteinlinked and enzyme-linked receptors?
What percentage of insulin receptors are spare?
What percentage of insulin receptors are spare?
What is the term used to describe systems that exhibit signal amplification?
What is the term used to describe systems that exhibit signal amplification?
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What is the percentage of adrenoceptors in the heart that are spare?
What is the percentage of adrenoceptors in the heart that are spare?
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What is the result of signal amplification in G proteinlinked and enzyme-linked receptors?
What is the result of signal amplification in G proteinlinked and enzyme-linked receptors?
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What is the primary function of receptors in the context of drug signaling?
What is the primary function of receptors in the context of drug signaling?
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Which of the following best describes the relationship between agonist binding and cellular response?
Which of the following best describes the relationship between agonist binding and cellular response?
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What is the functional significance of spare receptors in a system?
What is the functional significance of spare receptors in a system?
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Which type of receptors are characterized by signal amplification and spare receptors?
Which type of receptors are characterized by signal amplification and spare receptors?
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What is the consequence of signal amplification in G protein-linked and enzyme-linked receptors?
What is the consequence of signal amplification in G protein-linked and enzyme-linked receptors?
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What is the significance of the percentage of spare receptors in a system?
What is the significance of the percentage of spare receptors in a system?
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What is the effect of upregulation of β adrenoreceptors?
What is the effect of upregulation of β adrenoreceptors?
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What happens to the number of receptors in response to long-term administration of an agonist?
What happens to the number of receptors in response to long-term administration of an agonist?
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What is the consequence of spare receptors in a system?
What is the consequence of spare receptors in a system?
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What is the result of signal amplification in G protein–linked and enzyme-linked receptors?
What is the result of signal amplification in G protein–linked and enzyme-linked receptors?
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What is the effect of abrupt cessation of beta-blockers?
What is the effect of abrupt cessation of beta-blockers?
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What is the relationship between spare receptors and maximal response?
What is the relationship between spare receptors and maximal response?
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What is the effect of long-term administration of an antagonist on receptors?
What is the effect of long-term administration of an antagonist on receptors?
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What is the significance of spare receptors in the heart?
What is the significance of spare receptors in the heart?
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What is the effect of signal amplification on agonist binding?
What is the effect of signal amplification on agonist binding?
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What is the effect of desensitization of receptors?
What is the effect of desensitization of receptors?
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What is the term used to describe a physicochemical alteration in the receptor which makes it unresponsive to the drug?
What is the term used to describe a physicochemical alteration in the receptor which makes it unresponsive to the drug?
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What is the measure of the amount of drug necessary to produce an effect of a given magnitude?
What is the measure of the amount of drug necessary to produce an effect of a given magnitude?
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What is the formula used to calculate the therapeutic index?
What is the formula used to calculate the therapeutic index?
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What type of antagonism is based on the physical property of drugs?
What type of antagonism is based on the physical property of drugs?
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What type of antagonism is characterized by the binding of an antagonist to a site on the enzyme rather than the agonist site?
What type of antagonism is characterized by the binding of an antagonist to a site on the enzyme rather than the agonist site?
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What is the term used to describe the type of antagonism that occurs when opposite effects of two drugs on two different types of receptors antagonize each other?
What is the term used to describe the type of antagonism that occurs when opposite effects of two drugs on two different types of receptors antagonize each other?
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What is the term used to describe the type of antagonism that occurs when an antagonist binds to another site on the receptor?
What is the term used to describe the type of antagonism that occurs when an antagonist binds to another site on the receptor?
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Which of the following drugs is an example of a drug with a narrow therapeutic index?
Which of the following drugs is an example of a drug with a narrow therapeutic index?
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What is the result of increasing the concentration of a drug agonist in the presence of a competitive antagonist?
What is the result of increasing the concentration of a drug agonist in the presence of a competitive antagonist?
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What is the term used to describe the type of antagonism that occurs when an antagonist increases the metabolism and excretion of a drug?
What is the term used to describe the type of antagonism that occurs when an antagonist increases the metabolism and excretion of a drug?
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Study Notes
Receptors and Signal Transduction
- Drugs act as signals, and their receptors act as signal detectors.
- Agonist refers to a naturally occurring small molecule or a drug that binds to a site on a receptor protein and activates it.
Signal Amplification
- G protein–linked and enzyme-linked receptors can amplify signal intensity and duration via the signal cascade effect.
- Only a fraction of the total receptors for a specific ligand may need to be occupied to elicit a maximal response in systems with spare receptors.
- Spare receptors provide an immense functional reserve, ensuring adequate response.
- Example: Insulin receptors - about 99% are spare, ensuring adequate glucose entry into the cell.
- Example: β adrenoceptors in the heart - only about 5% to 10% are spare.
Receptors and Signal Transduction
- Drugs act as signals, and their receptors act as signal detectors.
- Agonist refers to a naturally occurring small molecule or a drug that binds to a site on a receptor protein and activates it.
Signal Amplification
- G protein–linked and enzyme-linked receptors can amplify signal intensity and duration via the signal cascade effect.
- Only a fraction of the total receptors for a specific ligand may need to be occupied to elicit a maximal response in systems with spare receptors.
- Spare receptors provide an immense functional reserve, ensuring adequate response.
- Example: Insulin receptors - about 99% are spare, ensuring adequate glucose entry into the cell.
- Example: β adrenoceptors in the heart - only about 5% to 10% are spare.
Signal Amplification
- G protein–linked and enzyme-linked receptors can amplify signal intensity and duration via the signal cascade effect.
- This amplification allows for a maximal response with only a fraction of the total receptors occupied, resulting in spare receptors.
- Spare receptors provide a functional reserve, ensuring adequate responses to ligands.
- For example, 99% of insulin receptors are spare, while only 5-10% of β adrenoceptors in the heart are spare.
Upregulation and Downregulation of Receptors
- Upregulation occurs when receptor activity is lower than usual, resulting in an increase in the number of receptors.
- Example: long-term administration of beta-blockers upregulates β adrenoreceptors, leading to rebound hypertension when stopped.
- Downregulation occurs due to repeated or long-term administration of an agonist, resulting in a decrease in the number of receptors.
- Desensitization of the receptor to the drug may also occur, making it unresponsive to the drug (tachyphylaxis).
Dose–Response Relationships
- Graded dose–response relationships occur when the concentration of a drug increases, resulting in a gradual increase in pharmacologic effect.
- Plotting the magnitude of response against increasing doses of a drug produces a graded dose–response curve shaped like a rectangular hyperbola.
- Potency is a measure of the amount of drug necessary to produce an effect of a given magnitude, often measured as EC50 (the concentration producing 50% of the maximum effect).
- Efficacy is the magnitude of response a drug causes when it interacts with a receptor.
Therapeutic Index
- The therapeutic index (TI) is calculated as TI = TD50 / ED50.
- A narrow therapeutic index indicates a small difference between the dose producing the desired effect and the dose producing toxicity.
- Examples: warfarin (narrow therapeutic index) and penicillin (wide therapeutic index).
Drugs Antagonism
- Pharmacological antagonists:
- Competitive: antagonists compete with agonists at the same receptor site, and can be overcome by increasing the concentration of the drug agonist.
- Non-competitive: antagonists bind irreversibly to a site on the enzyme, and cannot be overcome by increasing the concentration of the drug agonist.
- Physical antagonism: based on physical properties of drugs, such as adsorption (e.g., charcoal in alkaloidal poisoning).
- Chemical antagonism: based on drug-drug interaction, such as neutralization (e.g., NaHCO3 + HCl in hyperacidity).
- Physiological/Functional Antagonism: opposite effects of two drugs on different types of receptors, such as histamine and adrenaline.
- Pharmacokinetic antagonism: increasing the metabolism and excretion of a drug, such as enzyme induction.
- Allosteric antagonism: antagonist binds to another site on the receptor, such as verapamil on Ca++ receptors.
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Description
A short quiz on biology, covering receptors, signal transduction, and agonist binding. Questions are based on the principles of signal amplification and cellular responses.
