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Harper's Biochemistry Chapter 8 - Enzymes Kinetics Part 2

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What is the process called when a drug is resistant to degradation by enzymes present in the patient or pathogen? A) Drug absorption B) Drug excretion C) Drug metabolism D) Drug distribution E) Drug synthesis

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Explanation

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Drug Metabolism

What is the process called when a drug is resistant to degradation by enzymes present in the patient or pathogen?
A) Drug absorption
B) Drug excretion
C) Drug metabolism
D) Drug distribution
E) Drug synthesis

C) Drug metabolism
Explanation: Drug metabolism refers to the process where a drug is resistant to degradation by enzymes present in the patient or pathogen, which is crucial for minimizing effective dosage and potential side effects.

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Pharmacology and Enzyme Targets

What is one of the primary goals of pharmacology?
A) To increase the growth of pathogens
B) To impair the growth of invading pathogens
C) To decrease the body's defense mechanisms
D) To enhance the invasiveness of pathogens
E) To stimulate the production of toxins

B) To impair the growth of invading pathogens
Explanation: One of the primary goals of pharmacology is to identify agents that can destroy or impair the growth, invasiveness, or development of invading pathogens.

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Drug Metabolism

What role does enzyme kinetics play in drug metabolism?
A) It determines the drug's chemical structure
B) It identifies the drug's side effects
C) It analyzes and optimizes drug metabolism
D) It measures the drug's solubility
E) It evaluates the drug's color

C) It analyzes and optimizes drug metabolism
Explanation: Enzyme kinetics plays a central role in the analysis and optimization of drug metabolism, which is a key determinant of drug efficacy.

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Competitive and Noncompetitive Inhibitors

Why are noncompetitive inhibitors particularly desirable in drug development?
A) Their effects can be completely overcome by increases in substrate concentration
B) They do not affect the enzyme's activity
C) Their effects cannot be completely overcome by increases in substrate concentration
D) They increase the enzyme's activity
E) They are less potent than competitive inhibitors

C) Their effects cannot be completely overcome by increases in substrate concentration
Explanation: Noncompetitive inhibitors are particularly desirable because their effects cannot be completely overcome by increases in substrate concentration, making them more effective in inhibiting enzyme activity.

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Drug Development and Enzyme Inhibition

What is the role of 2′-Deoxy-5-fluorouridylic acid in cancer chemotherapy?
A) It inhibits HMG-CoA reductase
B) It blocks cell wall synthesis in bacteria
C) It inhibits thymidylate synthase
D) It inhibits angiotensin-converting enzyme
E) It stimulates endogenous defense mechanisms

C) It inhibits thymidylate synthase
Explanation: 2′-Deoxy-5-fluorouridylic acid is a potent inhibitor of thymidylate synthase, which is a common target in cancer chemotherapy.

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Competitive and Noncompetitive Inhibitors

How can the effects of simple competitive inhibitors be overcome?
A) By lowering the concentration of the substrate
B) By raising the concentration of the substrate
C) By increasing the enzyme concentration
D) By adding more inhibitors
E) By changing the pH of the reaction

B) By raising the concentration of the substrate
Explanation: The effects of simple competitive inhibitors, which typically resemble substrates, can be overcome by raising the concentration of the substrate.

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Multisubstrate Reactions

What type of inhibition pattern is observed in a random-order Bi-Bi reaction?
A) Noncompetitive inhibition
B) Competitive inhibition by each product in the absence of its coproduct
C) Uncompetitive inhibition
D) Mixed inhibition
E) No inhibition

B) Competitive inhibition by each product in the absence of its coproduct
Explanation: In a random-order Bi-Bi reaction, each product acts as a competitive inhibitor in the absence of its coproduct, regardless of which substrate is designated the variable substrate.

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Enzyme Kinetics

What is the primary reason for using initial rate conditions in enzyme-catalyzed reaction measurements?
A) To increase the reaction speed
B) To ensure the presence of product
C) To preclude the reverse reaction
D) To decrease enzyme activity
E) To stabilize the enzyme

C) To preclude the reverse reaction
Explanation: Initial rate conditions are used to effectively preclude the reverse reaction from taking place due to the virtual absence of product.

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Michaelis-Menten Kinetics

What do linear forms of the Michaelis-Menten equation simplify?
A) Determination of enzyme structure
B) Determination of Km and Vmax
C) Measurement of enzyme concentration
D) Analysis of enzyme inhibition
E) Calculation of reaction temperature

B) Determination of Km and Vmax
Explanation: Linear forms of the Michaelis-Menten equation simplify the determination of Km and Vmax.

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Drug Development and Enzyme Inhibition

Which enzyme is inhibited by statin drugs to lower cholesterol production?
A) Angiotensin-converting enzyme
B) Viral reverse transcriptase
C) HMG-CoA reductase
D) Alanyl alanine carboxypeptidase-transpeptidase
E) Thymidylate synthase

C) HMG-CoA reductase
Explanation: Statin drugs lower cholesterol production by inhibiting the enzyme HMG-CoA reductase.

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Cooperative Binding Kinetics

What does a Hill coefficient (n) greater than 1 indicate?
A) Negative cooperativity
B) No cooperativity
C) Positive cooperativity
D) Competitive inhibition
E) Noncompetitive inhibition

C) Positive cooperativity
Explanation: A Hill coefficient (n) greater than 1 indicates positive cooperativity in substrate-binding kinetics.

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Sequential and Ping-Pong Reactions

What is a characteristic feature of Ping-Pong reactions?
A) Formation of a ternary complex
B) Release of one or more products before all substrates have been added
C) Random order of substrate addition
D) Single-step transfer of a group from one substrate to another
E) Competitive inhibition

B) Release of one or more products before all substrates have been added
Explanation: Ping-Pong reactions involve the release of one or more products from the enzyme before all the substrates have been added, and they often involve covalent catalysis.

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Drug Development and Enzyme Inhibition

What is IC50 used to evaluate in pharmaceutical publications?
A) The maximum reaction velocity
B) The enzyme concentration
C) The effectiveness of an inhibitor
D) The substrate concentration
E) The reaction temperature

C) The effectiveness of an inhibitor
Explanation: IC50 is the concentration of inhibitor that produces 50% inhibition under the particular circumstances of an experiment and is widely used in pharmaceutical publications to evaluate the effectiveness of an inhibitor.

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Sequential and Ping-Pong Reactions

Which type of reaction involves the formation of a ternary complex before catalysis can proceed?
A) Ping-Pong reaction
B) Sequential reaction
C) Single-substrate reaction
D) Competitive inhibition
E) Noncompetitive inhibition

B) Sequential reaction
Explanation: In sequential reactions, both substrates must combine with the enzyme to form a ternary complex before catalysis can proceed.

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Sequential and Ping-Pong Reactions

How can you distinguish a ping-pong mechanism from a sequential mechanism using double-reciprocal plots?
A) Ping-pong mechanism yields intersecting lines
B) Sequential mechanism yields parallel lines
C) Ping-pong mechanism yields parallel lines
D) Sequential mechanism yields no lines
E) Both mechanisms yield the same pattern

C) Ping-pong mechanism yields parallel lines
Explanation: In double-reciprocal plots, a ping-pong mechanism yields parallel lines, whereas a sequential mechanism yields a pattern of intersecting lines.

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Michaelis-Menten Kinetics

What is the significance of Vmax in Bi-Bi reactions conforming to Michaelis-Menten kinetics?
A) It refers to the reaction rate when only one substrate is present
B) It is irrelevant in Bi-Bi reactions
C) It refers to the reaction rate attained when both substrates are present at saturating levels
D) It is the same as Km
E) It is always zero

C) It refers to the reaction rate attained when both substrates are present at saturating levels
Explanation: In Bi-Bi reactions conforming to Michaelis-Menten kinetics, Vmax refers to the reaction rate attained when both substrates are present at saturating levels.

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Competitive and Noncompetitive Inhibitors

What does the inhibitory constant (Ki) represent for simple competitive and noncompetitive inhibitors?
A) The rate of enzyme catalysis
B) The dissociation constant for the enzyme-substrate complex
C) The dissociation constant for the enzyme-inhibitor complex
D) The maximum reaction velocity
E) The substrate concentration at half-maximal velocity

C) The dissociation constant for the enzyme-inhibitor complex
Explanation: For simple competitive and noncompetitive inhibitors, the inhibitory constant (Ki) is equal to the dissociation constant for the relevant enzyme-inhibitor complex.

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Enzyme Kinetics

What does the study of enzyme kinetics reveal?
A) The overall change in free energy for a reaction
B) The individual steps by which enzymes transform substrates into products
C) The equilibrium constant of a reaction
D) The concentration of substrates and products at equilibrium
E) The ratio of reaction rate constants

B) The individual steps by which enzymes transform substrates into products
Explanation: The study of enzyme kinetics reveals the individual steps by which enzymes transform substrates into products, providing insights into the reaction mechanism.

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Sequential and Ping-Pong Reactions

In ping-pong reactions, when are one or more products released from the enzyme?
A) After all substrates have been added
B) Before all substrates have been added
C) Simultaneously with substrate binding
D) Only at the end of the reaction
E) During the initial rate phase

B) Before all substrates have been added
Explanation: In ping-pong reactions, one or more products are released from the enzyme before all the substrates have been added.

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