Biochemistry Quiz on Enzyme Inhibition

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Questions and Answers

What is a primary reason we cannot produce transition state analogs for drugs?

They require specific environmental conditions.

They are too expensive to produce.

They do not bind to enzymes effectively.

They are highly unstable. (correct)

What type of inhibitor is penicillin classified as?

Competitive inhibitor

Suicide inhibitor (correct)

Reversible inhibitor

Allosteric inhibitor

Which mechanism allows allopurinol to be an effective treatment for gout?

It mimics the substrate of xanthine oxidase.

It enhances the activity of xanthine oxidase.

It binds to xanthine oxidase irreversibly. (correct)

It increases urate production.

What important role does the β-lactam ring in penicillin play?

It resembles the transition-state complex in natural reactions. Signup and view all the answers

What component does the xanthine oxidase enzyme contain that contributes to its function?

Molybdenum-sulfide complex Signup and view all the answers

What effect does noncompetitive inhibition have on the Vmax of an enzyme?

Vmax decreases and KM remains the same Signup and view all the answers

What is the impact of competitive inhibitors on the KM of an enzyme?

KM increases Signup and view all the answers

In a situation of noncompetitive inhibition, what can be done to mitigate its effect?

Increase enzyme concentration Signup and view all the answers

Which statement correctly reflects the behavior of the enzyme in the analogy given?

Competitive inhibitors do not change the maximum capacity to open blue pins Signup and view all the answers

What relationship does the slope of the Lineweaver-Burk plot depict?

The slope is dependent on both KM and Vmax Signup and view all the answers

What is the primary reason enzymes require high regulation?

They can catalyze millions of reactions per second. Signup and view all the answers

Which characteristic distinguishes isozymes from each other?

Same substrate and product but differ in gene and localization. Signup and view all the answers

What is the Km value used to indicate in enzyme kinetics?

The substrate concentration at which the reaction rate is half of Vmax. Signup and view all the answers

What type of inhibitor permanently deactivates the enzyme?

Irreversible inhibitor. Signup and view all the answers

Which enzyme type has a low Km and is mitochondrial?

ALDH I. Signup and view all the answers

Which statement about hexokinase I and hexokinase IV is true?

Hexokinase I has a higher affinity for glucose than hexokinase IV. Signup and view all the answers

The inability of half of the Chinese and Japanese population to produce ALDH I can cause which effect?

Acetyl aldehyde toxicity. Signup and view all the answers

What is a characteristic of reversible inhibitors?

They can bind and be released without permanent change to the enzyme. Signup and view all the answers

What is the primary action of mechanism-based inhibitors?

They mimic or participate in an intermediate step of the catalytic reaction. Signup and view all the answers

How do organophosphorus inhibitors affect acetylcholinesterase?

They covalently bind to serine in the enzyme’s active site. Signup and view all the answers

What is a potential consequence of the inhibition of acetylcholinesterase by organophosphorus compounds?

Sustained muscle contraction leading to respiratory failure. Signup and view all the answers

Why should individuals take aspirin before surgery?

To inhibit the COX-2 reaction which can affect blood clotting. Signup and view all the answers

Which type of bonds do covalent inhibitors form with enzyme active site amino acids?

Covalent or extremely tight bonds. Signup and view all the answers

What is the primary function of transition state analogs?

To mimic the intermediates in an enzyme-catalyzed reaction. Signup and view all the answers

What reaction does aspirin inhibit in relation to prostaglandin endoperoxide synthase?

The COX-2 reaction, affecting blood clotting. Signup and view all the answers

Which of the following compounds is an example of a covalent inhibitor?

Aspirin (acetylsalicylic acid). Signup and view all the answers

What is the primary way lead causes toxicity in the central nervous system?

By replacing normal functional metals in enzymes Signup and view all the answers

Which factor remains unchanged in the presence of a competitive inhibitor?

Vmax Signup and view all the answers

In competitive inhibition, what happens to KM when substrate concentration increases significantly?

Increases as more inhibitor binds Signup and view all the answers

What distinguishes noncompetitive inhibition from competitive inhibition?

Noncompetitive inhibitors change enzyme structure without blocking substrate binding Signup and view all the answers

How does a competitive inhibitor interact with the enzyme?

By competing with the substrate for the active site Signup and view all the answers

What effect does a noncompetitive inhibitor have on the enzyme during the reaction?

It decreases the maximum reaction velocity Signup and view all the answers

What unique characteristic of a competitive inhibitor allows it to be overcome by high substrate concentrations?

It competes for the same binding site as the substrate Signup and view all the answers

Why was lead previously used in paint despite its toxicity?

It offered a sweet taste that attracted children Signup and view all the answers

What is the primary effect of allopurinol in the body?

It oxidizes to oxypurinol which inhibits urate production. Signup and view all the answers

How does methotrexate disrupt DNA synthesis?

By inhibiting the activity of DHFR. Signup and view all the answers

Which of the following statements about the structure of allopurinol is correct?

It has a different nitrogen and carbon arrangement compared to hypoxanthine. Signup and view all the answers

What role does tetrahydrofolate (THF) play in nucleotide synthesis?

It aids in converting DHF to THF. Signup and view all the answers

What type of compounds are known to bind tightly to functional groups in enzymes and can exhibit toxicity?

Heavy metals. Signup and view all the answers

Which metal is specifically noted for its interaction with sulfhydryl groups in enzymes?

Mercury. Signup and view all the answers

What effect does methotrexate have on cell proliferation?

It prevents cell proliferation by disrupting nucleotide synthesis. Signup and view all the answers

How does the solubility of urate affect joint health?

Low solubility causes crystals to form and can lead to inflammation. Signup and view all the answers

Study Notes

Biochemistry: Enzyme Regulation

Enzymes are highly regulated due to their high processivity (catalyzing millions of reactions per second). Any mistake in their function would have significant consequences.

Modes of Enzyme Regulation

Isozymes (isoenzymes): These enzymes have the same substrate and product but differ in their gene, localization, kinetic parameters (Km, Vmax, kcat).
- Example: Hexokinases (I and IV). Hexokinase I (in RBCs) has a low Km (0.1 mM), while Hexokinase IV (in liver and pancreas) has a high Km (10 mM). This difference relates to the higher glucose requirement of RBCs compared to the liver, which can utilize other energy sources.
- Isozymes alter the enzyme's shape (conformation) which impacts its efficiency.
Blood glucose levels impact enzyme function.
- During low blood glucose, hexokinase I (in RBCs) can still effectively phosphorylate glucose even though blood glucose levels are below 5 mM.
- The high Km of hepatic glucokinase (hexokinase IV) promotes glucose storage in the liver.

Enzyme Regulation: Inhibitors

Inhibitors interfere with enzyme function, slowing reaction rates.
- Irreversible inhibitors react with the enzyme to inactivate it permanently.
- Reversible inhibitors bind and release the enzyme, allowing it to function normally again.

Mechanism-Based Inhibitors (Irreversible)

Mimic or participate in intermediate steps of the catalytic reaction.
- These decrease active enzyme concentrations.

Covalent Inhibitors

Form covalent or extremely strong bonds with active site amino acids.
Serve as targets for drugs and toxins:
- Example: Organophosphates (e.g., sarin, malathion, parathion), which covalently modify serine in acetylcholinesterase, leading to sustained muscle contraction, respiratory failure, and death.

Transition State Analogs

Transition state analogs resemble the transitory intermediate states of enzyme-catalyzed reactions.
They bind more strongly to the enzyme than the substrate, making them potent inhibitors.
Examples:
- Penicillin: A transition state analog of the bacterial enzyme transpeptidase, crucial for cell wall synthesis.
- Allopurinol: An inhibitor of xanthine oxidase, used to treat gout by decreasing urate production; it commits enzyme suicide by converting to a transition state analog.

Heavy Metal Inhibitors

Heavy metals (Hg, Pb, Al, Fe) can bind tightly to enzymes, often at reactive sulfhydryl groups.
Heavy metal binding can cause significant damage to enzymes resulting in enzyme inhibition.
Example: Lead replaces essential metals (e.g., calcium, iron, zinc) in regulatory proteins, impacting the central nervous system and other tissues.

Types of Reversible Inhibitors

Competitive inhibitors: Structurally similar to the substrate. These inhibitors bind to the active site, competing with the actual substrate for binding. Increasing substrate concentration overcomes the inhibition.
Noncompetitive inhibitors: Bind to a site other than the active site, causing a conformational change that reduces the enzyme's catalytic ability. Substrate binding is still possible but does not yield the expected product. Increasing substrate concentration does not overcome the inhibition.

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Description

Test your knowledge on enzyme inhibition and drug mechanisms with this quiz. Explore key concepts surrounding transition state analogs, penicillin classification, and the role of important components in enzyme function. Perfect for students studying biochemistry and pharmacology.