Enzyme Function and Active Sites

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Questions and Answers

How do enzymes accelerate reactions in biological systems?

By decreasing the time it takes for a reaction to reach equilibrium. (correct)
By directly providing energy to the reactants.
By increasing the activation energy required for the reaction.
By altering the equilibrium constant of the reaction.

What is the primary role of enzymes in biological systems?

To serve as structural components of cells.
To act as catalysts and speed up reactions. (correct)
To store genetic information.
To transport molecules across cell membranes.

Which of the following best describes the interaction between a ligand and its binding site?

A reversible association mediated by non-covalent and or covalent bonds. (correct)
A random encounter without any specific affinity.
A strong, irreversible interaction that permanently activates the target.
A permanent, covalent bond that alters the ligand's structure.

Which of the following is an example of a ligand?

A hormone. (A) Signup and view all the answers

What is the significance of the binding site (active site) on an enzyme?

It is where the substrate binds and the reaction occurs. (B) Signup and view all the answers

How do enzymes affect the activation energy of a reaction?

They decrease the activation energy. (A) Signup and view all the answers

How would you describe the bonds between the ligand and binding site?

Covalent and Non-covalent bonds. (C) Signup and view all the answers

Which of the following statements accurately describes enzymes?

Enzymes are globular proteins that act as catalysts. (D) Signup and view all the answers

Which amino acid side chain is MOST likely to engage in pi-stacking interactions within an enzyme's active site?

Phenylalanine (B) Signup and view all the answers

An enzyme active site contains a negatively charged amino acid residue. Which of the following interactions is MOST likely to occur?

Electrostatic attraction of positively charged residues (D) Signup and view all the answers

In enzyme catalysis, what is the PRIMARY role of bringing reactants together and positioning them correctly?

To weaken bonds in the reactants (C) Signup and view all the answers

Which amino acids are MOST likely to participate directly in acid-base catalysis within an enzyme's active site?

Histidine and Cysteine (A) Signup and view all the answers

Which aspect of enzyme catalysis does the induced fit model BEST explain?

The change in enzyme shape upon substrate binding and the specificity of enzymes (D) Signup and view all the answers

According to the induced fit model, what happens to the enzyme's active site when the substrate binds?

It undergoes a conformational change to better fit the substrate. (D) Signup and view all the answers

Which amino acid side chain can MOST readily act as a nucleophile in enzyme catalysis?

Lysine (A) Signup and view all the answers

What is the PRIMARY role of covalent bonds in enzyme catalysis?

To form a temporary enzyme-substrate intermediate. (D) Signup and view all the answers

Which type of interaction involves attraction between closely aligned nonpolar atoms of an enzyme and a substrate?

Van der Waals forces (D) Signup and view all the answers

What is primarily responsible for the specificity of a chemical binding site for its substrate?

The arrangement of complementary amino acid residues. (A) Signup and view all the answers

Which of the following amino acid pairs are most likely to participate in ionic interactions within a binding site?

Lysine and Arginine (C) Signup and view all the answers

In a binding site, what is the role of hydrophobic interactions?

To exclude water and stabilize nonpolar regions. (A) Signup and view all the answers

What type of interaction would most likely occur between a hydroxyl group on an amino acid in the binding site and a functional group on the substrate?

Hydrogen bond (A) Signup and view all the answers

If a mutation in an enzyme's binding site replaces a valine residue with glutamic acid, how might this affect substrate binding?

Introduce electrostatic repulsion (B) Signup and view all the answers

An inhibitor molecule binds tightly to the active site of an enzyme but does not undergo any chemical change. Which type of interaction is LEAST likely to be involved in this binding?

Covalent bonds (B) Signup and view all the answers

An enzyme's optimal activity is observed at a specific pH. Altering the pH significantly affects the ionization state of amino acid residues in the active site. What type of interaction would be MOST directly affected by this pH change?

Ionic interactions (B) Signup and view all the answers

An enzyme's allosteric site is BEST described as:

A region distinct from the active site that can influence enzyme activity upon binding a molecule. (A) Signup and view all the answers

Which of the following BEST illustrates the concept of 'induced fit' in enzyme-substrate interactions?

The enzyme's active site changes shape slightly to better accommodate the substrate. (A) Signup and view all the answers

An enzyme's specificity for its substrate is primarily due to:

The unique shape and chemical properties of the enzyme's binding site. (A) Signup and view all the answers

Compared to a rigid lock-and-key model, how does the flexibility of an enzyme's binding site contribute to its function?

It enables a tighter, more precise fit with the substrate, optimizing catalysis. (B) Signup and view all the answers

Which of the following is LEAST likely to be a feature that dictates the binding specificity between an enzyme and its substrate?

The enzyme's ability to permanently alter the substrate's chemical structure before binding. (B) Signup and view all the answers

An inhibitor binds to an enzyme and distorts the active site. This is an example of:

Allosteric inhibition (B) Signup and view all the answers

An enzyme is most complementary to:

The transition state (C) Signup and view all the answers

Which statement is NOT true about the enzyme-substrate complex:

It increases the energy of activation. (A) Signup and view all the answers

How is $V_{max}$ determined from a Lineweaver-Burk plot?

By calculating the reciprocal of the y-intercept. (C) Signup and view all the answers

Which of the following statements correctly describes the relationship between $K_m$ and the affinity of an enzyme for its substrate?

A low $K_m$ indicates strong binding affinity because the enzyme requires a lower substrate concentration to reach half of $V_{max}$. (A) Signup and view all the answers

How is $K_m$ calculated from the x-intercept in a Lineweaver-Burk plot?

$K_m$ is equal to the negative value of the x-intercept. (D) Signup and view all the answers

What does the Michaelis-Menten constant ($K_m$) represent?

The substrate concentration at half the maximum reaction rate. (C) Signup and view all the answers

In a Michaelis-Menten plot, how is $V_{max}$ typically determined?

By locating the point on the curve where the reaction velocity (V) no longer increases with increasing substrate concentration. (D) Signup and view all the answers

How does $K_m$ relate to the affinity of an enzyme for its substrate?

A higher $K_m$ indicates a lower affinity. (B) Signup and view all the answers

How does a Lineweaver-Burk plot differ from a Michaelis-Menten plot in representing enzyme kinetics?

The Lineweaver-Burk plot is a double reciprocal plot, resulting in a straight line, while the Michaelis-Menten plot is a curve. (C) Signup and view all the answers

What does $V_{max}$ primarily reflect regarding enzyme kinetics?

The enzyme's catalytic capacity when the substrate is saturated. (B) Signup and view all the answers

What does a low $K_m$ value suggest about the enzyme-substrate interaction, and how does it affect the reaction rate at low substrate concentrations?

A low $K_m$ indicates strong binding, allowing the enzyme to achieve a significant reaction rate even at low substrate concentrations. (A) Signup and view all the answers

If an enzyme's $V_{max}$ is increased but the $K_m$ remains the same, what can be inferred about the enzyme's behavior?

The enzyme's efficiency at high substrate concentrations has improved. (D) Signup and view all the answers

Which statement best describes isozymes?

They catalyze the same reaction but differ in primary structure and tissue distribution. (D) Signup and view all the answers

What is the main difference between the structure of an enzyme and its isozymes?

Isozymes differ in their primary structure. (C) Signup and view all the answers

In a Lineweaver-Burk plot, how are $V_{max}$ and $K_m$ determined from the graph?

$V_{max}$ is the inverse of the y-intercept, and $K_m$ is the negative inverse of the x-intercept. (A) Signup and view all the answers

Which of the following scenarios would result in an increased $K_m$ value for an enzyme?

A mutation that weakens the enzyme's binding affinity for its substrate. (A) Signup and view all the answers

How can isozymes be useful targets in drug discovery?

By targeting a specific isozyme, drugs can achieve greater tissue specificity and reduce side effects. (C) Signup and view all the answers

How would you interpret a Michaelis-Menten curve that shows a high $V_{max}$ and a high $K_m$?

The enzyme has a low affinity for its substrate, but can achieve a high maximum reaction rate when substrate concentration is not limiting. (C) Signup and view all the answers

Flashcards

Enzyme

Globular proteins that act as biological catalysts, speeding up reactions by lowering the activation energy.

Binding/Active site

The specific area on an enzyme where a substrate binds.