Enzyme Action Mechanism and Factors

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Questions and Answers

What distinguishes irreversible inhibitors from other types of inhibitors?

They covalently modify the enzyme. (correct)

They increase the Km value of substrates.

They temporarily inhibit enzyme activity.

They can be easily reversed by increasing substrate concentration.

Which effect can result from the inhibition of acetylcholinesterase by diisopropyl fluorophosphate (DFP)?

Paralysis or death. (correct)

Enhanced muscle activity.

Increased nerve impulse transmission.

Improved enzymatic functioning.

What is a common therapeutic application of enzyme inhibitors?

To increase the effectiveness of all enzymes.

To promote enzyme activity in tumor cells.

To reduce the toxicity of antiviral drugs.

To lower arterial blood pressure through ACE inhibition. (correct)

Which class of drugs is exemplified by captopril, an enzyme inhibitor?

Antihypertensive agents Signup and view all the answers

Which of the following statements about enzyme inhibitors is true?

Certain synthetic drugs act as enzyme inhibitors with limited toxicity. Signup and view all the answers

What does Vmax represent in the Michaelis–Menten equation?

The maximum velocity obtainable by the reaction Signup and view all the answers

Why is Km important in enzyme kinetics?

It reflects the binding affinity of the enzyme for its substrate Signup and view all the answers

How does a high Km value affect enzyme-substrate binding affinity?

It indicates low binding affinity Signup and view all the answers

What type of curve is derived from plotting Vo against [S] in enzyme kinetics?

Hyperbolic curve Signup and view all the answers

What information can be obtained from a Lineweaver–Burk plot?

Exact values of Vmax and Km Signup and view all the answers

What happens to an enzyme when the temperature increases significantly?

It is denatured and loses its catalytic activity. Signup and view all the answers

What does a low Km value indicate about an enzyme-substrate pair?

The enzyme binds to the substrate with high affinity Signup and view all the answers

How does a change in pH affect enzyme activity?

It can denature the enzyme at extreme pH levels. Signup and view all the answers

Which statement describes the measurement of Vo in enzyme kinetics?

It is measured during the first few minutes of reaction Signup and view all the answers

Which statement is true regarding enzyme concentration and substrate concentration?

Increased enzyme concentration can increase the reaction rate when substrate is unlimited. Signup and view all the answers

What occurs as the substrate concentration increases past the saturation point?

The reaction rate remains constant despite additional substrate. Signup and view all the answers

What effect does increasing substrate concentration have on the reaction rate until Vmax is reached?

The reaction rate increases until a saturation point Signup and view all the answers

What effect can accumulating end-products have on enzyme activity?

They can cause a change in the surrounding pH. Signup and view all the answers

How do enzymes function at low concentrations?

They can catalyze reactions multiple times due to reusability. Signup and view all the answers

Which of the following describes an effect of temperature on enzyme function?

Extreme temperatures can lead to denaturation of the enzyme. Signup and view all the answers

What is a consequence of changing the pH outside an enzyme's optimum range?

It can lead to a loss of activity due to denaturation. Signup and view all the answers

What is the effect of uncompetitive inhibitors on the enzyme's efficiency?

They decrease both Km and Vmax. Signup and view all the answers

How does the binding of an inhibitor at a site other than the active site affect the enzyme?

It may change the enzyme's shape, affecting substrate binding. Signup and view all the answers

What distinguishes irreversible inhibitors from other types of enzyme inhibitors?

They permanently alter the enzyme's structure. Signup and view all the answers

What happens to Vmax and Km when an irreversible inhibitor is present?

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

Which of the following statements about the double reciprocal plot for uncompetitive inhibition is correct?

It displays parallel lines to that of the uninhibited enzyme. Signup and view all the answers

Heavy metal ions like mercury affect enzyme activity by:

Breaking disulphide bonds and altering enzyme shape. Signup and view all the answers

In non-competitive inhibition, how does the inhibitor interact with the enzyme?

It can bind to both the enzyme and the enzyme-substrate complex. Signup and view all the answers

What is a key characteristic of enzyme inhibition by covalent modification?

It can lead to complete loss of enzyme function. Signup and view all the answers

What is a characteristic feature of competitive inhibitors?

They occupy the active site of the enzyme. Signup and view all the answers

How does competitive inhibition affect Km?

Km increases. Signup and view all the answers

Which compound is an example of a competitive inhibitor that interferes with microbial growth?

Sulphonamides Signup and view all the answers

What does the presence of a competitive inhibitor indicate on a double reciprocal plot?

A shift in the x-intercept. Signup and view all the answers

In the context of competitive inhibition, how does substrate concentration affect the reaction rate?

Increased substrate concentration increases the reaction rate. Signup and view all the answers

What is the EI complex in competitive inhibition?

The complex formed between the inhibitor and enzyme. Signup and view all the answers

Which enzyme is specifically mentioned as being inhibited by malonic acid?

Succinic dehydrogenase Signup and view all the answers

What is the incorrect result of competitive inhibition on enzyme kinetics?

Decreased maximum reaction rate. Signup and view all the answers

What effect does a non-competitive inhibitor have on the Vmax of an enzyme?

Vmax decreases Signup and view all the answers

How does a non-competitive inhibitor alter the shape of the enzyme?

By forming a complex at a site other than the active site Signup and view all the answers

What happens to the Km value when a non-competitive inhibitor is present?

Km remains unaffected Signup and view all the answers

Which of the following statements is true regarding uncompetitive inhibitors?

They bind specifically to the enzyme-substrate complex Signup and view all the answers

What is a key characteristic of non-competitive inhibitors regarding substrate concentration?

Substrate concentration has no effect on inhibitor binding Signup and view all the answers

Which example illustrates non-competitive inhibition?

Cyanide binding to cytochrome oxidase Signup and view all the answers

What type of complexes are formed by non-competitive inhibitors when binding occurs?

Binary and ternary complexes Signup and view all the answers

How does the binding of a non-competitive inhibitor affect the enzyme's efficiency?

Decreases efficiency due to shape change Signup and view all the answers

Study Notes

Mechanism of Enzyme Action

Enzymes are typically proteins with a unique shape (conformation).
Within the enzyme molecule is an active site with specific properties to bind tightly to the substrate(s).
Enzyme-substrate interactions are explained by different theories:
- Lock and key model: The active site of the enzyme is complementary in shape to the substrate. The substrate fits into the active site like a key into a lock.
- Induced fit model: The active site changes shape slightly as the substrate binds, fitting tightly to the substrate. This accommodates the transition state.
- Transition state theory: Enzymes bind to the transition state complex more strongly than to the reactants, accelerating the reaction.

Factors Affecting Enzyme Rate

Temperature: Increasing temperature increases kinetic energy, leading to more frequent collisions between enzyme and substrate, and increasing the reaction rate. However, high temperatures denature the enzyme, losing its catalytic activity irreversibly.
pH: Changes in pH alter the ionic charge of acidic and basic groups within the enzyme, affecting its shape and active site function. Each enzyme has an optimal pH range for efficient activity; outside this range, enzyme activity decreases. Extremes of pH may denature the enzyme.
Enzyme concentration: At low enzyme concentrations the reaction rate increases with enzyme concentration but plateaus eventually at high enzyme concentrations.
Substrate concentration: Increasing substrate concentration increases the reaction rate up to the saturation point where all enzyme active sites are occupied. Further increase in substrate concentration does not increase the rate.
End-product concentration: Accumulation of end-products can alter the pH of the medium and can inhibit enzyme activity by negative feedback (combining with the enzyme).
Inhibition: Inhibitors, small molecules can reduce enzyme activity. Inhibition can be reversible or irreversible.

Types of Inhibition

Reversible inhibition: The inhibitor is easily removed from the enzyme, causing no permanent damage.
- Competitive inhibition: The inhibitor resembles the substrate, competing for the active site of the enzyme. Increasing substrate concentration can overcome competitive inhibition.
- Non-competitive inhibition: The inhibitor binds to a site other than the active site, changing the enzyme's shape and thus reducing activity. Increasing substrate concentration does not overcome non-competitive inhibition.
- Uncompetitive inhibition: The inhibitor binds only to the enzyme-substrate complex (ES), preventing the reaction. Both Km and Vmax decrease.
Irreversible inhibition: The inhibitor irreversibly binds to the enzyme, permanently altering its shape and thus inactivating the enzyme. Heavy metal ions and certain toxins can cause irreversible inhibition.

Michaelis-Menten Kinetics

The Michaelis-Menten model describes the relationship between reaction rate and substrate concentration.
It assumes a single substrate, higher substrate concentration than enzyme, and initial velocity is measured.
Vmax is the maximum reaction rate possible by an enzyme-catalyzed reaction when the active sites are completely saturated with substrate.
Km is the Michaelis constant and signifies the substrate concentration at which the reaction rate is half of Vmax. A low Km indicates high substrate affinity.

Lineweaver-Burk Plot

A double reciprocal plot (1/V vs. 1/[S]) of the Michaelis-Menten equation produces a straight line.
The slope and y-intercept of this line can be used to determine Km and Vmax, which can help reveal mechanisms of enzyme inhibition.

Therapeutic Applications of Enzyme Inhibitors

Several drugs and natural compounds act as enzyme inhibitors to treat various conditions, such as hypertension, hypercholesterolaemia, or cancer.
Competitive inhibitors are similar to substrates in structure, which also shows how they can be used to treat diseases. Different types of inhibitors affect different types of enzymes.

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Description

Explore the intricate mechanisms of enzyme action, including the guiding theories of enzyme-substrate interactions such as the lock and key model and the induced fit model. Learn how various factors, particularly temperature, affect the rate of enzyme reactions. This quiz covers essential concepts that will deepen your understanding of enzyme functionality in biological systems.