Elm 3 Drug Binding

Question 1

Q: What does the Hill-Langmuir equation describe?

Answer 1

A: The interaction of a drug with its target, governing drug binding and affinity.

Question 2

Q: Define Kd (equilibrium dissociation constant).

Answer 2

A: A measure of affinity that represents the concentration of a drug that produces 50% of maximum binding.

Question 3

Q: What is Bmax?

Answer 3

A: The maximum binding of a drug in a tissue sample, indicating the number of binding sites available.

Question 4

Q: How is affinity defined in the context of drug-receptor interactions?

Answer 4

A: The tightness of binding of a drug to its target.

Question 5

Q: What does selectivity refer to in pharmacology?

Answer 5

A: The relative affinity of a drug for one receptor type compared to another, usually expressed as a ratio of two Kd values.

Question 6

Q: Describe the Michaelis-Menten equation.

Answer 6

A: A version of the Hill-Langmuir equation that describes how the rate of an enzyme-catalyzed reaction varies with substrate concentration.

Question 7

Q: What is Km in the Michaelis-Menten equation?

Answer 7

A: The Michaelis constant, a measure of an enzyme’s affinity for its substrate.

Question 8

Q: Define Vmax.

Answer 8

A: The maximal velocity of an enzyme-catalyzed reaction, which is the product of enzyme concentration and the catalytic constant.

Question 9

Q: What does the Law of Mass Action state?

Answer 9

A: The rate of a reaction is directly proportional to the concentration of the reactants.

Question 10

Q: How does Kd relate to affinity?

Answer 10

A: As Kd decreases, affinity increases.

Question 11

Q: What type of curve does the Hill-Langmuir equation produce when plotting B (bound receptors) vs. [D] (drug concentration)?

Answer 11

A: A rectangular hyperbola.

Question 12

Q: What are radioligands?

Answer 12

A: Radiolabeled drugs used to quantify how much of a drug has bound to receptors in a tissue sample.

Question 13

Q: Name the three steps in a radioligand binding assay.

Answer 13

A: Incubate, separate, and quantify.

Question 14

Q: What is non-specific binding (NSB) in a radioligand binding assay?

Answer 14

A: Binding of the radioligand to non-receptor sites, which represents a large, unsaturable pool of low-affinity binding sites.

Question 15

Q: How is specific binding calculated in a radioligand binding assay?

Answer 15

A: Specific binding = Total binding - Non-specific binding (NSB).

Question 16

Q: What are common radioligands used in assays?

Answer 16

A: Tritium (³H), Carbon-14 (¹⁴C), and Iodine-125 (¹²⁵I).

Question 17

Q: Describe the process of separating bound radioligand from free radioligand in an assay.

Answer 17

A: Filtration or centrifugation, where the assay passes through a glass fiber filter that retains membranes but allows free radioligand to pass through.

Question 18

Q: What are the methods used to measure the amount of radioactivity in a radioligand binding assay?

Answer 18

A: Liquid scintillation counting (LSC) for beta emitters and gamma counting for gamma emitters.

Question 19

Q: What is the purpose of a saturation assay?

Answer 19

A: To determine the equilibrium dissociation constant (Kd) and the maximum binding (Bmax) for a radioligand in a tissue of interest.

Question 20

Q: What are some limitations of saturation assays?

Answer 20

A: They require radioactive versions of all drugs being investigated, are time-consuming and costly to produce, and generate radioactive waste that is expensive to dispose of.

Question 21

Q: How can the limitations of saturation assays be overcome?

Answer 21

A: By using competition binding assays, which do not require radioactive versions of all drugs and are less resource-intensive.

Question 22

Q: What information can be obtained from comparing drug affinities using saturation assays?

Answer 22

A: Affinity comparisons can be made by dividing the Kd of a drug with lower affinity by the Kd of a drug with higher affinity.

Question 23

Q: Why is information about affinity and selectivity important in drug development?
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Answer 23

A: It helps pharmaceutical companies identify drugs that are highly selective for their target, minimizing potential side effects.

Question 24

Flashcard 6:
Q: How does the Michaelis-Menten equation relate to enzyme kinetics?

Answer 24

A: It describes the rate of an enzyme-catalyzed reaction as a function of substrate concentration.

Question 25

Q: What is Km in the Michaelis-Menten equation?

Answer 25

A: The Michaelis constant, which is a measure of the substrate’s affinity for the enzyme.

Question 26

Q: What does Vmax represent in enzyme kinetics?

Answer 26

A: The maximum rate of the reaction, which is achieved when all enzyme molecules are saturated with substrate.

Question 27

Q: How is Vmax related to enzyme concentration?

Answer 27

A: Vmax is directly proportional to enzyme concentration.

Question 28

Q: What does the catalytic constant (Kcat) represent in enzyme kinetics?

Answer 28

A: It measures the efficiency of an enzyme at converting substrate into product.