Enzyme Inhibition Types

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Questions and Answers

What is the role of allopurinol in the treatment of gout?

It promotes the formation of hypoxanthine.

It inhibits the enzyme xanthine oxidase. (correct)

It enhances uric acid production.

It serves as a structural analog of xanthine.

How do sulfonamides function as competitive inhibitors?

By enhancing bacterial growth.

By mimicking a structural analog of PABA. (correct)

By promoting folic acid synthesis.

By directly inhibiting protein synthesis.

What is the effect of statins on cholesterol levels?

They lower plasma cholesterol levels. (correct)

They act as allosteric inhibitors of enzymes.

They have no effect on HMG-CoA reductase.

They increase cholesterol synthesis.

What characterizes competitive inhibitors like warfarin?

They are structural analogs of vitamin K. Signup and view all the answers

What is the primary function of competitive inhibitors?

To compete with substrate for the active site. Signup and view all the answers

What does the Lineweaver-Burk plot help visualize?

The kinetics of enzyme reactions. Signup and view all the answers

What distinguishes allosteric inhibitors from competitive inhibitors?

They cause conformational changes in the enzyme. Signup and view all the answers

Which of the following enzymes is inhibited by statins?

HMG-CoA reductase. Signup and view all the answers

What is the primary clinical application of acid phosphatase?

Detecting prostate cancer Signup and view all the answers

Which enzyme is primarily associated with parotitis?

Amylase Signup and view all the answers

Which enzyme's principal source includes the pancreas and salivary glands?

Amylase Signup and view all the answers

What clinical application is primarily linked to lactate dehydrogenase?

Tumor marker and hepatic parenchymal diseases Signup and view all the answers

Which enzyme is primarily indicated in muscle diseases and myocardial infarction?

Creatine kinase Signup and view all the answers

What happens to the reaction velocity as substrate concentration increases until the enzyme is saturated?

The reaction velocity increases to a maximum value. Signup and view all the answers

What does a smaller value of Km indicate about an enzyme?

The enzyme has a higher affinity for its substrate. Signup and view all the answers

Which of the following best describes the Lineweaver-Burk plot?

It is a transformation of the Michaelis-Menten equation into a straight line. Signup and view all the answers

At what temperature does enzyme action virtually stop?

0 °C Signup and view all the answers

What is the primary effect of rising temperature on enzyme reactions?

Increased kinetic energy and reaction velocity. Signup and view all the answers

Which statement accurately describes the Michaelis-Menten equation?

It relates the initial velocity to substrate concentration and Km. Signup and view all the answers

In a Lineweaver-Burk plot, what does the y-intercept represent?

1/Vmax Signup and view all the answers

What does Km denote in enzyme kinetics?

The substrate concentration that achieves half of Vmax. Signup and view all the answers

What happens to enzyme activity if the temperature exceeds its optimum level?

The reaction rate decreases due to denaturation. Signup and view all the answers

What is the optimum temperature for most animal enzymes?

37 °C Signup and view all the answers

How does pH affect enzyme activity?

Slight changes in pH can significantly affect activity. Signup and view all the answers

Which type of enzyme inhibition is characterized by inhibitors that are structurally similar to the substrate?

Competitive inhibition Signup and view all the answers

What is the result of a competitive inhibitor on the Km value?

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

At what pH is pepsin, a digestive enzyme in the stomach, maximally active?

pH 2 Signup and view all the answers

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

It can eventually overcome the inhibition. Signup and view all the answers

What occurs to enzyme activity when pH deviates significantly from the optimum?

It stops due to denaturation and irreversible inhibition. Signup and view all the answers

What is the effect of allosteric inhibitors on enzyme activity?

Decrease the affinity for the substrate and decrease Vmax Signup and view all the answers

What characterizes feedback inhibition in enzyme activity?

It involves the binding of the end product at the allosteric site Signup and view all the answers

Which of the following describes antienzymes?

They specifically inactivate the enzyme they bind to Signup and view all the answers

What type of inhibitor is aspirin, and how does it act?

Inhibitor of hydroxyl groups through acetylation of serine Signup and view all the answers

Which mechanism do fluoride ions utilize to inhibit enzymes?

By chelating essential metal ions required for enzyme activity Signup and view all the answers

Which statement about irreversible enzyme inhibitors is incorrect?

They lead to temporary changes in enzyme activity Signup and view all the answers

How is the rate of metabolic reactions controlled in organisms?

Through various mechanisms including changing enzyme activity Signup and view all the answers

Cyanide and carbon monoxide inhibit which type of enzyme?

Enzymes of the respiratory chain that contain heme Signup and view all the answers

Study Notes

Competitive Inhibition

Competitive inhibitors are structurally similar to the substrate and bind reversibly at the active or catalytic site.
The effect of competitive inhibitors can be reversed by increasing the substrate concentration.
Competitive inhibitors increase the apparent Km for a given substrate, requiring more substrate to achieve half maximal velocity.

Allosteric Inhibition

Small organic molecules bind to a specific site away from the catalytic site.
Conformational changes in the protein structure lead to decreased enzyme activity.
Allosteric inhibitors decrease the enzyme's affinity for its substrate (increase Km), decrease maximal catalytic activity (decrease Vmax), or both.

Feedback Inhibition

Inhibition of the activity of an enzyme in a pathway by the end products of that pathway.
End products bind to an allosteric site on the regulatory key enzyme.
Prevents the accumulation of unwanted amounts of metabolic end products.

Irreversible Enzyme Inhibition

Inhibitor effects are permanent, often by destroying or modifying the enzyme.
Examples include denaturing agents, antienzymes, and inhibitors that block chemical groups.

Effect of Substrate Concentration

The velocity of the reaction increases as substrate concentration increases, up to a point of enzyme saturation.
The Michaelis constant (Km) is the substrate concentration that produces half the maximal velocity (Vmax).
A smaller Km reflects a higher affinity of the enzyme for its substrate, and vice versa.

Effect of Temperature

Enzyme activity stops at 0°C due to molecule movement inhibition.
As temperature rises, reaction velocity increases up to the optimum temperature due to increased kinetic energy and collisions.
Activity stops around 70°C due to enzyme protein denaturation.
Optimum temperatures vary: ~37°C for most animal enzymes, ~50°C for plant enzymes.

Effect of pH

Each enzyme has an optimal pH for maximal activity.
Activity decreases as pH deviates from the optimum.
Slight pH changes alter substrate and catalytic site charges, impacting activity.
Extreme pH changes cause denaturation and irreversible inhibition.
Most enzymes have optima between pH 5 and 9, with exceptions like pepsin (optimum pH 2).

Clinically Important Enzymes and Diagnostic Applications

Acid phosphatase: Red cells and prostate, used in diagnosing prostate cancer.
Alanine aminotransferase (ALT): Liver, used for assessing hepatic parenchymal diseases.
Alkaline phosphatase: Liver, bone, intestinal mucosa, and placenta; used in diagnosing bone diseases and hepatobiliary diseases.
Amylase: Salivary glands and pancreas, used in diagnosing parotitis and pancreatitis.
Aspartate aminotransferase (AST): Liver, skeletal muscle, and heart; used in diagnosing hepatic parenchymal diseases, muscle, and cardiac diseases.
Creatine kinase: Skeletal muscle and heart, used in diagnosing muscle diseases and myocardial infarction.
Lactate dehydrogenase (LDH): Heart, liver, skeletal muscle, erythrocytes, platelets, and lymph nodes; used in diagnosing hemolysis, hepatic parenchymal diseases, and as a tumor marker.

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Description

This quiz covers the different types of enzyme inhibition, including competitive, allosteric, and feedback inhibition. You will learn how these mechanisms affect enzyme activity and the importance of substrate concentration. Test your understanding of enzyme kinetics and regulatory processes.