Enzyme Functions and Catalysis Quiz
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Questions and Answers

What role do enzymes play in biochemical reactions?

  • They decrease the activation energy and alter ΔG.
  • They change the equilibrium of reactions.
  • They increase the reaction rates without being consumed. (correct)
  • They always require ATP to function.

    • Which statement correctly differentiates between a holoenzyme and an apoenzyme?

  • An apoenzyme is active without a cofactor.
  • Both holoenzyme and apoenzyme are proteins.
  • A holoenzyme is always a RNA molecule.
  • A holoenzyme contains a cofactor, while an apoenzyme does not. (correct)

    • What is the physiological significance of enzymes?

  • They create energy by lowering ΔG in reactions.
  • They maintain body equilibrium at all temperatures.
  • They regulate biochemical reactions at body temperature and pH. (correct)
  • They replace the need for chemical catalysts.

    • Which type of cofactor can be considered a prosthetic group?

    <p>Tightly bound cofactors</p> Signup and view all the answers

    Why is it important to understand enzyme mechanisms?

    <p>To develop effective therapeutic agents like antibiotics.</p> Signup and view all the answers

    What happens to the overall ΔG free energy of a reaction when enzymes are used?

    <p>It remains unchanged.</p> Signup and view all the answers

    Which of the following statements about ribozymes is accurate?

    <p>Ribozymes are RNA molecules that can catalyze reactions.</p> Signup and view all the answers

    Which factor is commonly required by some enzymes to function properly?

    <p>Cofactors or coenzymes</p> Signup and view all the answers

    What is a common characteristic of enzymes?

    <p>They are specific for their substrates.</p> Signup and view all the answers

    What is the primary role of substrate in enzyme activity?

    <p>Serves as a positive stimulator for synthesis</p> Signup and view all the answers

    Which statement best describes irreversible inhibitors?

    <p>They permanently inactivate the enzyme by reacting with it.</p> Signup and view all the answers

    How do reversible inhibitors affect enzyme activity?

    <p>They can dissociate from the enzyme after binding.</p> Signup and view all the answers

    What is the result of an irreversible inhibitor's action on an enzyme?

    <p>One molecule of inhibitor can permanently deactivate one enzyme molecule.</p> Signup and view all the answers

    Which of the following statements is true regarding bacterial ADP-ribosylating exotoxins?

    <p>They transfer an ADP-Ribose moiety of NAD+ to target proteins.</p> Signup and view all the answers

    What occurs when a reversible inhibitor binds to the free enzyme?

    <p>It prevents the binding of the substrate.</p> Signup and view all the answers

    What dietary precursor is required for the coenzyme Biocytin?

    <p>Biotin</p> Signup and view all the answers

    Which of the following coenzymes is responsible for transferring acyl groups?

    <p>Coenzyme A</p> Signup and view all the answers

    Which coenzyme is derived from Pantothenic acid?

    <p>Coenzyme A</p> Signup and view all the answers

    What type of chemical group does Flavin adenine dinucleotide transfer?

    <p>Electrons</p> Signup and view all the answers

    Which coenzyme does not have a dietary requirement?

    <p>Lipoate</p> Signup and view all the answers

    Which statement about chymotrypsin is true?

    <p>Chymotrypsin is classified as a serine protease.</p> Signup and view all the answers

    What is the first step in the chymotrypsin mechanism?

    <p>Substrate binding occurs.</p> Signup and view all the answers

    What is the function of Tetrahydrofolate in biochemical processes?

    <p>Transferring one-carbon groups</p> Signup and view all the answers

    Which of the following describes the action of allosteric regulators?

    <p>Allosteric effectors can either positively or negatively modulate enzymatic catalysis.</p> Signup and view all the answers

    The dietary precursor for Nicotinamide adenine dinucleotide is:

    <p>Niacin</p> Signup and view all the answers

    How do the kinetics of allosteric regulators differ from Michaelis-Menten kinetics?

    <p>Allosteric kinetics do not exhibit a distinct Vmax.</p> Signup and view all the answers

    Which coenzyme is primarily involved in the transfer of amino groups?

    <p>Pyridoxal phosphate</p> Signup and view all the answers

    Which vitamin corresponds to the dietary precursor of Flavin adenine dinucleotide?

    <p>Vitamin B2</p> Signup and view all the answers

    What stage follows the nucleophilic attack in the chymotrypsin mechanism?

    <p>Substrate cleavage.</p> Signup and view all the answers

    Which coenzyme is involved in the transfer of hydride ions?

    <p>Nicotinamide adenine dinucleotide</p> Signup and view all the answers

    What modifies enzyme activity through covalent means?

    <p>Covalent modification.</p> Signup and view all the answers

    Which of the following is NOT a component involved in enzyme functionality?

    <p>Plasticizer.</p> Signup and view all the answers

    Which process occurs after water attacks in the chymotrypsin mechanism?

    <p>The product dissociates from the enzyme.</p> Signup and view all the answers

    What is an example of a coenzyme that participates in various catalytic reactions?

    <p>CoA (Coenzyme A).</p> Signup and view all the answers

    What correctly describes noncovalent modifications?

    <p>They typically involve small chemical molecules that modify activity.</p> Signup and view all the answers

    What is the role of enzymes in relation to activation barriers during chemical reactions?

    <p>They decrease the activation energy needed for the reaction.</p> Signup and view all the answers

    How do enzymes organize substrates to lower ΔG‡?

    <p>By forming a fairly rigid enzyme-substrate (ES) complex.</p> Signup and view all the answers

    What is the significance of binding energy in enzyme activity?

    <p>It helps to organize substrates into a transition state.</p> Signup and view all the answers

    Which of the following statements about enzyme active sites is true?

    <p>Active sites best bind the transition states.</p> Signup and view all the answers

    Who proposed the idea that enzymes bind transition states better than substrates?

    <p>Linus Pauling</p> Signup and view all the answers

    Which inorganic ion is NOT listed as a cofactor for enzymes?

    <p>Fe4+</p> Signup and view all the answers

    What happens during the transition state compared to the ground state regarding enzyme interactions?

    <p>Stronger/additional interactions occur with the transition state.</p> Signup and view all the answers

    Which of the following enzymes is associated with the cofactor K+?

    <p>Hexokinase</p> Signup and view all the answers

    What effect do uncatalyzed reactions have compared to enzyme-catalyzed reactions?

    <p>They may have unorganized reactants leading to unfavorable transitions.</p> Signup and view all the answers

    Which of the following cofactors is associated with the enzyme arginase?

    <p>Mn2+</p> Signup and view all the answers

    Study Notes

    Enzyme Functions and Catalysis

    • Enzymes are highly specific biological catalysts that regulate biochemical reactions without being consumed or altering equilibrium.
    • Reactions are accelerated by enzymes, increasing reaction rates by factors ranging from 10^5 to 10^17.
    • Most enzymes are proteins; however, some RNA molecules (ribozymes) can also have catalytic functions.

    Enzyme Structure

    • Enzymes may require cofactors, which can be:
      • Inorganic ions (e.g., Fe++, Mg++, Zn++)
      • Organic coenzymes (e.g., NADP, heme)
    • A holoenzyme includes the cofactor, whereas an apoenzyme lacks it.
    • Prosthetic groups are closely bound cofactors; other cofactors may be loosely associated.

    Mechanism of Enzymatic Catalysis

    • Enzymes do not affect the overall free energy change (ΔG) of reactions but lower the activation energy (ΔG‡).
    • Enzymes organize reactive groups into optimal proximity and orientation, facilitating transition states.
    • The concept introduced by Linus Pauling states that enzymes bind transition states more effectively than substrates, lowering activation barriers.

    Cofactors and Coenzymes

    • Important cofactors include:
      • Cu2+ for cytochrome oxidase
      • Fe2+/Fe3+ for catalase, peroxidase
      • Mg2+ for hexokinase
      • Zn2+ for carboxypeptidases
    • Coenzymes facilitate the transfer of specific functional groups (e.g., Coenzyme A for acyl groups, NAD for hydride ions) and have dietary precursors.

    Enzyme Classifications

    • Enzymes are categorized based on their functions and reaction mechanisms; they follow saturation kinetics where reaction velocity does not proportionally increase with substrate concentration.

    Chymotrypsin and Its Mechanism

    • Chymotrypsin, a serine protease, hydrolyzes peptide bonds adjacent to aromatic amino acids.
    • The catalytic mechanism includes:
      • Substrate binding
      • Nucleophilic attack
      • Cleavage of the peptide bond
      • Water molecule activation to assist in cleavage
      • Product release

    Regulation of Enzyme Activity

    • Enzyme activity can be regulated through:
      • Noncovalent modification (allosteric regulation)
      • Covalent modifications
      • Reversible/irreversible inhibitors
    • Allosteric regulators can enhance or inhibit enzyme activity, demonstrating different kinetics compared to Michaelis-Menten enzymes.

    Enzyme Inhibition

    • Inhibitors reduce enzyme activity:
      • Irreversible inhibitors permanently deactivate enzymes, often functioning as toxins or drugs.
      • Reversible inhibitors associate with enzymes but can be displaced; they include competitive and non-competitive inhibitors.
    • Examples of irreversible inhibitors include bacterial ADP-ribosylating exotoxins, such as cholera and diphtheria toxins.

    Key Terms

    • Understand the definitions and roles of:
      • Holoenzyme, apoenzyme, cofactor, coenzyme, substrate, active site, and prosthetic group.
    • Study specific catalytic mechanisms and key amino acids involved in enzyme reactions, particularly regarding chymotrypsin.

    Physiological Significance

    • Enzymes are vital for life, facilitating numerous biochemical reactions necessary for metabolism, DNA replication, and cellular repair mechanisms under physiological conditions.

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    Biochem Exam 2 PDF

    Description

    Test your knowledge on enzymes, their functions, and catalysis. This quiz covers enzyme structure, the role of cofactors, and the mechanisms of enzymatic catalysis. Challenge yourself with questions that will deepen your understanding of these vital biological catalysts.

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