HBF 102: Enzymes II - Inhibition & Regulation

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Questions and Answers

What effect does phosphorylation have on glycogen phosphorylase?

Has no effect on its activity

Inhibits its synthesis

Increases its activity (correct)

Decreases its activity

Which statement is true regarding the effect of elevated insulin levels?

It represses enzyme synthesis in all physiological conditions

It induces the synthesis of enzymes for glucose metabolism (correct)

It decreases the synthesis of enzymes for glucose metabolism

It has no effect on enzyme synthesis

How long does it typically take for alterations in enzyme levels due to induction or repression of synthesis to occur?

Minutes

Seconds

Hours to days (correct)

Weeks

What is the primary change observed in competitive inhibition?

Increased Km Signup and view all the answers

How do noncompetitive inhibitors primarily affect enzyme kinetics?

Only decrease Vmax Signup and view all the answers

Which enzyme's activity is decreased by the addition of phosphate?

Glycogen synthase Signup and view all the answers

What role do heavy metals generally play in enzyme function?

They prevent substrate binding Signup and view all the answers

What is the impact of covalent modification on enzyme activity compared to allosteric regulation?

Covalent modification takes seconds to minutes Signup and view all the answers

What is the main difference between induction and repression of enzyme synthesis?

Induction increases enzyme levels; repression decreases them Signup and view all the answers

What happens to the apparent Km in the presence of a competitive inhibitor?

It increases due to the inhibitor competing with the substrate. Signup and view all the answers

Which of the following best characterizes non-competitive inhibition?

It does not change the Km value of the enzyme. Signup and view all the answers

How does non-competitive inhibition affect the Lineweaver-Burk plot?

The apparent Vmax decreases while Km remains unchanged. Signup and view all the answers

Which of the following statements about non-competitive inhibitors is TRUE?

They prevent the reaction regardless of substrate concentration. Signup and view all the answers

Which scenario exemplifies non-competitive inhibition?

Heavy metal ions binding to enzymes, preventing catalysis. Signup and view all the answers

Which of the following is NOT a characteristic of competitive inhibitors?

They decrease the Vmax of the reaction. Signup and view all the answers

In the context of competitive inhibition, what does a change in apparent Km indicate?

The inhibitor affects the enzyme's active site efficiency. Signup and view all the answers

How do non-competitive inhibitors influence enzyme kinetics?

They decrease Vmax without affecting Km. Signup and view all the answers

What role does glucose-6-phosphate play in the regulation of hexokinase?

It acts as a non-competitive inhibitor. Signup and view all the answers

What is the primary characteristic of competitive inhibition in enzyme reactions?

The inhibitor competes with the substrate for the active site. Signup and view all the answers

How does a competitive inhibitor affect the Km value of an enzyme-catalyzed reaction?

It increases the Km value. Signup and view all the answers

In a Lineweaver-Burk plot, the lines for competitive inhibition intersect at which axis?

y-axis Signup and view all the answers

What type of bond do reversible inhibitors typically use to bind with enzymes?

Noncovalent bonds Signup and view all the answers

Which of the following statements about irreversible inhibitors is true?

They bind covalently to enzymes. Signup and view all the answers

What is the effect of increasing substrate concentration in the presence of a competitive inhibitor?

It can reverse the effect of the inhibitor. Signup and view all the answers

Which of the following correctly describes the effect of a non-competitive inhibitor?

It decreases Vmax without affecting Km. Signup and view all the answers

Which type of inhibition is characterized by the formation of an enzyme-inhibitor complex that does not compete for the active site?

Non-competitive inhibition Signup and view all the answers

What is the effect of a competitive inhibitor on the rate of formation of the enzyme-substrate complex?

It decreases the formation rate. Signup and view all the answers

What is a key indicator that a reaction is undergoing competitive inhibition when analyzing Lineweaver-Burk plots?

Lines have different slopes but intersect on the y-axis. Signup and view all the answers

What is the role of allosteric effectors in enzyme regulation?

They bind at a site other than the active site and can alter enzyme affinity for substrate. Signup and view all the answers

What distinguishes a homotropic effector from a heterotropic effector?

Homotropic effectors are identical to the substrate while heterotropic effectors are different. Signup and view all the answers

Which of the following best describes negative effectors?

They inhibit enzyme activity. Signup and view all the answers

How does feedback inhibition regulate enzyme activity?

By allowing the end-product to inhibit an earlier enzyme in the pathway. Signup and view all the answers

What is the primary function of protein kinases in enzyme regulation?

To catalyze the addition of phosphate groups using ATP. Signup and view all the answers

What effect does phosphorylation generally have on enzymes?

It can either increase or decrease enzyme activity. Signup and view all the answers

What do phosphoprotein phosphatases do in enzyme regulation?

They remove phosphate groups from phosphorylated enzymes. Signup and view all the answers

Which statement about allosteric enzymes is true?

Allosteric enzymes demonstrate cooperativity among substrates. Signup and view all the answers

What happens when the concentration of the end-product G increases in a metabolic pathway?

It inhibits the enzyme responsible for its own synthesis. Signup and view all the answers

Which of the following is a limiting factor in enzyme activity regulation through phosphorylation?

The concentration of ATP in the reaction. Signup and view all the answers

Study Notes

Course Information

Faculty: Medicine
Academic Year: 2024-2025
Year: 1
Semester: 1
Module: Human Body Function (HBF) 102
Module Specific Topic: Enzymes II: Enzyme Inhibition & Regulation

Enzyme Inhibition

Enzyme inhibition occurs when a substance reduces the speed of an enzyme-catalyzed reaction.
Inhibitors can be irreversible (bind covalently) or reversible (bind non-covalently).
Reversible inhibitors are further categorized as competitive and non-competitive.

Competitive Inhibition

In competitive inhibition, the inhibitor competes with the substrate for the active site.
The inhibitor binds reversibly to the active site that the substrate would normally occupy.
Consequently, the substrate cannot bind.
Increasing substrate concentration reverses this effect
Competitive inhibition increases the apparent Km but does not change Vmax.
In a Lineweaver-Burk plot, competitive inhibition shows a change in the x-intercept, but not the y-intercept.

Non-Competitive Inhibition

In non-competitive inhibition, the inhibitor does not compete with the substrate for the active site.
It binds to a different site on the enzyme.
This binding changes the enzyme's shape, impacting its ability to bind the substrate.
Non-competitive inhibition reduces Vmax but does not change Km.
In a Lineweaver-Burk plot, non-competitive inhibition shows a change in the y-intercept, but not the x-intercept.
Heavy metals are an example of non-competitive inhibitor

Allosteric Inhibition

Allosteric enzymes are regulated by molecules called effectors (or modifiers).
Modifiers bind non-covalently at a site other than the active site.
This binding can alter the enzyme's affinity for its substrate or its maximal catalytic activity.
Positive effectors increase enzyme activity, while negative effectors decrease it.
Homotropic effectors are the substrate itself;
Heterotropic effectors are different from the substrate. Examples are feedback inhibition.

Covalent Modification

Many enzymes can be regulated by adding or removing phosphate groups from specific amino acid residues (serine, threonine, or tyrosine).
Phosphorylation reactions are catalyzed by protein kinases.
Dephosphorylation is catalyzed by phosphatases.
Phosphorylation can increase or decrease an enzyme's activity.

Induction and Repression

Enzymes may be regulated by the rates of their synthesis or degradation.
Increased or decreased synthesis affects the total number of active enzyme sites.
This process is slower than allosteric or covalent modification.

Interactive Question Examples

Correct answer: Captopril inhibition can be relieved by increasing substrate concentration.
Correct answer: Heavy metal enzyme inhibitors bind to different sites than the active site.

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Description

Explore the concept of enzyme inhibition in this quiz focusing on competitive and non-competitive inhibitors. Understand how these inhibitors affect enzyme-catalyzed reactions, including their impact on kinetic parameters like Km and Vmax. Test your knowledge on the mechanisms and implications of enzyme regulation.