Enzymes: Catalysts in Biochemistry

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Questions and Answers

What is an apoenzyme?

An enzyme without its cofactor (correct)

An enzyme that catalyzes reactions at high pH only

An enzyme that has undergone a structural change

An enzyme in its active form with a cofactor

How do enzyme cofactors affect enzymatic activity?

They increase the pH of the reaction environment

They convert the enzyme into a different protein type

They decrease the activation energy of the reaction (correct)

They act as substrates in the reaction

What is the primary characteristic of the active site of an enzyme?

It is complementary in shape to the substrate upon binding (correct)

It is where the substrate and product are released

It has a fixed shape that does not change during enzyme function

It prevents enzyme-substrate complexes from forming

Which of the following statements about proteolytic enzymes is correct?

They break peptide bonds among amino acids Signup and view all the answers

What is a characteristic feature of the induced-fit model of enzyme function?

The substrate binds and then the enzyme adapts its shape Signup and view all the answers

What does a negative Gibbs Free Energy change (ΔG < 0) indicate about a reaction?

The reaction will produce more product until equilibrium is reached. Signup and view all the answers

How does the presence of an enzyme affect a chemical reaction?

It lowers the activation energy required to reach the transition state. Signup and view all the answers

In Michaelis-Menten kinetics, what does Km represent?

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

Which statement correctly describes the relationship between reaction rate and reactant concentration in first-order reactions?

The reaction rate is directly proportional to the reactant concentration. Signup and view all the answers

What does kcat represent in enzyme kinetics?

The maximum rate of product formation when the enzyme is fully saturated. Signup and view all the answers

What is the main purpose of the Lineweaver-Burk plot?

To simplify the determination of kinetic parameters. Signup and view all the answers

In a Lineweaver-Burk plot, how is $K_M$ determined?

As the negative reciprocal of the x-intercept. Signup and view all the answers

What type of plot is created by plotting $V$ against $V/[S]$?

Eadie-Hofstee diagram. Signup and view all the answers

What characteristic is common to allosteric enzymes?

They have multiple active sites located on different subunits. Signup and view all the answers

What happens when an allosteric inhibitor binds to an enzyme?

All active sites become less effective. Signup and view all the answers

What type of regulation involves a regulator molecule binding to an enzyme at a site other than the active site?

Allosteric regulation. Signup and view all the answers

In cooperativity, how does a substrate affect other active sites on an allosteric enzyme?

It enhances their activity once one active site is occupied. Signup and view all the answers

The slope of an Eadie-Hofstee plot represents what kinetic parameter?

The negative value of $K_M$. Signup and view all the answers

Which of the following statements about competitive and noncompetitive inhibition is correct?

Only competitive inhibition can be reversed by increasing substrate concentration. Signup and view all the answers

Chymotrypsin is an example of which type of enzymatic behavior?

Enzyme that obeys Michaelis–Menten kinetics. Signup and view all the answers

Study Notes

Enzymes: Remarkable Catalysts

Enzymes speed up biochemical reactions.
Most enzymes are proteins, some are RNA.
Enzymes stabilize the transition state, the high-energy point in a reaction.
Enzymes function optimally at specific temperatures and pH levels.

Enzymes Catalyze Highly Specific Reactions

Reactants in enzyme-catalyzed reactions are called substrates.
Enzymes are highly specific, like proteolytic enzymes that hydrolyze peptide bonds between amino acids.

Proteases Readily Break Peptide Bonds

Proteases are enzymes that catalyze the breaking of peptide bonds.

Many Enzymes Require Cofactors for Activity

Enzyme cofactors are non-protein molecules or ions that assist enzymes.

Active Sites of Enzymes

Enzymes have catalytic and binding sites.
The catalytic site facilitates the conversion of substrates to products.
The binding site, or active site, is highly specific allowing enzymes to interact selectively with substrates.
The lock-and-key model suggests a rigid active site that is complementary to the substrate.
The induced-fit model proposes a flexible active site that changes shape to fit the substrate.

Thermodynamics and Enzymes

Gibbs Free Energy (G) is a useful thermodynamic function for understanding enzymes.
The change in Gibbs free energy (ΔG) determines the direction of a reaction (ΔG < 0, proceeds to the right; ΔG > 0, proceeds to the left).
Enzymes do not change the equilibrium of a reaction, but they accelerate the rate of reaction.
Reactions with a negative ΔG will release energy.

Michaelis-Menten Kinetics

Km is the Michaelis-Menten constant, a measure of the enzyme's affinity for the substrate.
Vmax is the maximal reaction rate.
kcat is the turnover number, a measure of the enzyme's catalytic efficiency.
Enzyme kinetics are typically mathematical.

Allosteric Regulation

Allosteric regulation involves a regulatory molecule binding to the enzyme at a site other than the active site.
This alters the enzyme's activity.
Competitive inhibition occurs when a molecule similar to the substrate competes for the active site.
Noncompetitive inhibition occurs when the inhibitor binds to a separate site, reducing enzyme function.

Examples of Enzymes that do not obey Michaelis-Menten Kinetics

Some enzymes, like allosteric enzymes, do not follow Michaelis-Menten kinetics because of their cooperative substrate binding.

Proteases

Proteases use a catalytic triad to break peptide bonds.
Proteases show intricate mechanisms.

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Description

Explore the remarkable world of enzymes and their role as catalysts in biochemical reactions. This quiz covers enzyme specificity, the role of cofactors, and the significance of active sites. Test your knowledge on how enzymes operate and the essential functions they perform.