Enzyme Mechanisms and Specificity Quiz
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Questions and Answers

What type of specificity allows an enzyme to act on only one kind of functional group?

  • Stereospecificity
  • Group specificity (correct)
  • Absolute specificity
  • Linkage specificity

Which mechanism of catalysis involves an enzyme using side chains to donate or accept protons?

  • Covalent catalysis
  • Proximity
  • Acid-base catalysis (correct)
  • Metal ion catalysis

What role does Zn²⁺ play in the function of carbonic anhydrase?

  • It acts as an enzyme's active site template
  • It increases the overall thermodynamics
  • It forms covalent bonds with substrates
  • It stabilizes the negative charge and polarizes water molecules (correct)

Which statement best describes transition state stabilization?

<p>Active sites promote transition state intermediates (D)</p> Signup and view all the answers

Which type of specificity refers to an enzyme's ability to selectively catalyze one stereoisomer over another?

<p>Stereospecificity (C)</p> Signup and view all the answers

In enzyme reactions, what is primarily affected when increasing the concentration of substrate?

<p>Enzyme saturation kinetics (A)</p> Signup and view all the answers

Which mechanism involves amino acid side chains forming temporary covalent bonds with substrates?

<p>Covalent catalysis (D)</p> Signup and view all the answers

Which mechanism of enzyme action is NOT relevant for isomerases?

<p>Proximity (B)</p> Signup and view all the answers

What happens to enzyme synthesis when tryptophan levels are high?

<p>Repressor protein binds, halting enzyme synthesis. (C)</p> Signup and view all the answers

Which mechanism prevents self-digestion of digestive enzymes?

<p>Activation by zymogens. (B)</p> Signup and view all the answers

How does phosphorylation affect glycogen synthase and glycogen phosphorylase?

<p>Glycogen phosphorylase is activated while glycogen synthase is inactivated. (C)</p> Signup and view all the answers

What role does ATP play in the function of Aspartate Transcarbamoylase?

<p>It activates the enzyme and enhances pyrimidine synthesis. (A)</p> Signup and view all the answers

What is a characteristic of multifunctional enzymes?

<p>They possess multiple catalytic activities on a single polypeptide chain. (A)</p> Signup and view all the answers

Which of the following statements regarding allosteric control is true?

<p>Binding of a ligand can shift the enzyme between tense and relaxed states. (D)</p> Signup and view all the answers

What is the effect of decreasing lactose consumption after weaning on lactase enzyme synthesis?

<p>There is a decrease in lactase enzyme transcription. (A)</p> Signup and view all the answers

What is the primary reason for the cleavage of chymotrypsinogen into active α-chymotrypsin?

<p>To prevent self-digestion during transport. (B)</p> Signup and view all the answers

What is the role of the aspartic acid side chain in the catalytic triad of chymotrypsin?

<p>It takes a proton from the histidine side chain. (A)</p> Signup and view all the answers

What does a lower Km value indicate about an enzyme's substrate affinity?

<p>The reaction can proceed with a smaller amount of substrate. (C)</p> Signup and view all the answers

In the context of enzyme kinetics, what occurs when the substrate concentration exceeds Km?

<p>The enzyme reaction rate reaches Vmax. (C)</p> Signup and view all the answers

What is the function of the electrostatic catalysis in the enzymatic reaction described?

<p>To stabilize the negative charge of the substrate. (C)</p> Signup and view all the answers

Which step in chymotrypsin's mechanism involves the formation of a tetrahedral transition state?

<p>The hydrolysis of the peptide bond. (D)</p> Signup and view all the answers

What effect does a saturated enzyme have on the rate of reaction as substrate concentration increases?

<p>The rate of reaction levels off and becomes independent of substrate concentration. (C)</p> Signup and view all the answers

Which factor is CRUCIAL for maintaining the pH during the enzymatic reaction involving bicarbonate?

<p>The proton released maintains pH balance. (C)</p> Signup and view all the answers

What reaction does lysozyme primarily catalyze through acid-base catalysis?

<p>Hydrolysis of glycosidic bonds in carbohydrates. (D)</p> Signup and view all the answers

Flashcards

Enzyme Stereospecificity

Enzymes' ability to selectively catalyze reactions of one stereoisomer over another.

Enzymatic Absolute Specificity

An enzyme catalyzes only one specific reaction.

Enzyme Group Specificity

Enzymes that act on a specific functional group of a molecule.

Enzyme Linkage Specificity

Enzymes that act on a particular type of chemical bond.

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Enzyme Catalytic Power

Enzymes increase reaction rates by orders of magnitude, often up to 10^12 times.

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Activation Energy

The energy needed for a reaction to proceed to the transition state.

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Enzyme Proximity Effect

Enzymes bring reactants closer together in the active site and arrange them to have more favorable collisions, decreasing entropy.

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Acid-Base Catalysis

Enzymes use weak acid or base side chains to facilitate reactions by donating or accepting protons, stabilizing the transition state.

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Gene Expression Regulation (e.g., Trp, Lac)

Levels of substrates or products control enzyme synthesis. High levels of a product inhibit further synthesis; low levels allow resumption of enzyme production.

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Zymogen Activation

Inactive digestive enzymes (zymogens) are cleaved to become active, preventing self-digestion.

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Covalent Modification

Phosphorylation (adding a phosphate group) and dephosphorylation (removing it) change an enzyme's activity through polarity changes.

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Feedback Inhibition

The end product of a reaction inhibits its own synthesis to prevent overproduction..

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Allosteric Regulation

Enzyme activity is altered by the binding of a molecule (activator or inhibitor) at a site other than the active site, changing the enzyme shape.

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Allosteric Effector

A molecule that binds to an enzyme, causing a change in its shape, thus altering enzyme activity.

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Multifunctional Enzyme

A single polypeptide chain with multiple catalytic activities.

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Blood Clotting Cascade

A series of enzymatic activations where one factor activates another, ultimately forming a blood clot.

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What is the role of OH- in carbonic anhydrase?

Hydroxide ions (OH-) attack carbon dioxide molecules, forming bicarbonate ions (HCO3-) and releasing a proton (H+). This process helps maintain pH balance.

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How does lysozyme catalyze the breakdown of bacterial cell walls?

Lysozyme employs general acid catalysis, electrostatic catalysis, and transition state catalysis. It uses glutamic acid to donate a proton, forming a positively charged transition state, and aspartate to balance the charge. Finally, hydrolysis breaks the glycosidic bond.

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What is the catalytic triad in chymotrypsin?

The catalytic triad consists of three amino acid residues: Serine, Histidine, and Aspartic acid. These residues form a charge relay system that allows for efficient polypeptide hydrolysis.

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How does chymotrypsin hydrolyze polypeptides?

Chymotrypsin uses its catalytic triad to hydrolyze polypeptides. Histidine removes a proton from serine, creating a reactive intermediate. This intermediate attacks the peptide bond, forming a tetrahedral transition state. Water then enters the active site to complete the reaction.

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What is a covalent acyl enzyme intermediate?

A covalent acyl enzyme intermediate forms when the enzyme's active site forms a covalent bond with the substrate during catalysis. This intermediate is crucial for the catalytic cycle.

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What are the assumptions of Michaelis-Menten kinetics?

Michaelis-Menten kinetics assumes a single substrate, reversible binding, negligible reverse reaction, and excess substrate compared to enzyme concentration.

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What is Vmax?

Vmax is the maximum rate of an enzymatic reaction when the enzyme is fully saturated with substrate. It represents the highest possible reaction rate under given conditions.

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What is Km?

Km is the Michaelis constant, which represents the substrate concentration at which the reaction rate is half of Vmax. It reflects the affinity of the enzyme for its substrate.

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