Biochemistry I - CHM219: Enzyme Kinetics
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Questions and Answers

What is the metabolic role of the nicotinamide portion in NAD+?

  • It acts as an irreversible catalyst.
  • It serves as an oxidizing agent. (correct)
  • It is involved in peptide bond formation.
  • It acts solely as a reducing agent.

    • Which enzyme class is responsible for oxidation-reduction reactions?

  • Lyases
  • Hydrolases
  • Oxidoreductases (correct)
  • Transferases

    • How does the zinc ion assist in the function of carboxypeptidase A?

  • It catalyzes the hydrolysis without any effect on charge.
  • It stabilizes the negative charge on the oxygen during the reaction. (correct)
  • It transfers functional groups between molecules.
  • It directly hydrolyzes peptide bonds.

    • What does the IUBMB enzyme classification number EC 3.4.21.5 indicate?

    <p>It belongs to the hydrolase class with a specific subclass.</p> Signup and view all the answers

    Which of the following statements about ribozymes is true?

    <p>They can catalyze specific phosphodiester bond hydrolysis.</p> Signup and view all the answers

    What is feedback control in enzyme regulation primarily aimed at?

    <p>The efficient regulation of complex metabolic pathways.</p> Signup and view all the answers

    What is the primary function of transferases?

    <p>They transfer functional groups between molecules.</p> Signup and view all the answers

    Which reaction exemplifies the action of NAD+ as an oxidizing agent?

    <p>Conversion of alcohols to aldehydes or ketones.</p> Signup and view all the answers

    What characterizes a competitive inhibitor in enzyme kinetics?

    <p>It competes with the substrate for the active site.</p> Signup and view all the answers

    How can the dissociation constant of a competitive inhibitor, KI, be determined?

    <p>From the slope of a Lineweaver-Burk plot at varying [I].</p> Signup and view all the answers

    What is the effect of an uncompetitive inhibitor on enzyme kinetics?

    <p>It affects the catalytic event and reduces both Vmax and KM.</p> Signup and view all the answers

    What distinguishes mixed inhibition from competitive and uncompetitive inhibition?

    <p>The inhibitor binds to the enzyme and alters substrate affinity.</p> Signup and view all the answers

    What happens to the Vmax and KM values in a Lineweaver-Burk plot with mixed inhibition?

    <p>Vmax decreases and KM increases.</p> Signup and view all the answers

    What does an Eadie-Hofstee plot directly graph?

    <p>Velocity versus the ratio of velocity to substrate concentration</p> Signup and view all the answers

    What occurs during irreversible inhibition via adduct formation?

    <p>The enzyme's active site becomes permanently altered.</p> Signup and view all the answers

    Which of the following describes the role of cofactors and vitamins in enzyme function?

    <p>They assist in enzyme catalysis and are often derived from vitamins.</p> Signup and view all the answers

    Which type of substrate binding requires one substrate to bind before another?

    <p>Ordered Substrate Binding</p> Signup and view all the answers

    What does the presence of a covalent bond between an irreversible inhibitor and an enzyme indicate?

    <p>The enzyme becomes completely inactive.</p> Signup and view all the answers

    What is the primary effect of a competitive inhibitor on KM?

    <p>It increases apparent KM.</p> Signup and view all the answers

    In the Ping-Pong mechanism, what happens after a substrate is bound?

    <p>A product is released and a second substrate binds.</p> Signup and view all the answers

    Which of the following statements is true about enzyme inhibition?

    <p>Enzyme inhibition can be both reversible and irreversible.</p> Signup and view all the answers

    Which characteristic distinguishes random substrate binding from ordered substrate binding?

    <p>Requirement of sequential binding</p> Signup and view all the answers

    How can the effects of an amino acid mutation in an enzyme active site be analyzed?

    <p>By observing effects on substrate binding (KM) and transition-state stabilization (kcat).</p> Signup and view all the answers

    What is a key feature of the Lineweaver-Burk plot?

    <p>It is a double-reciprocal plot used to determine KM and kcat.</p> Signup and view all the answers

    What role do kinases play in the regulation of enzyme activity?

    <p>They phosphorylate target residues such as serine, threonine, or tyrosine.</p> Signup and view all the answers

    What happens to zymogens during their activation process?

    <p>They become catalytically active through proteolytic cleavage.</p> Signup and view all the answers

    How does the blood clotting cascade initiate?

    <p>Through exposure of blood to damaged tissue surfaces or internal trauma.</p> Signup and view all the answers

    What is the result of thrombin acting on fibrinogen?

    <p>It removes fibrinopeptides to allow monomer association.</p> Signup and view all the answers

    Which of the following correctly describes the structural changes during chymotrypsinogen activation?

    <p>Cleavage between specific amino acids leads to the formation of active forms.</p> Signup and view all the answers

    What is the role of disulfide bonds during the activation of pancreatic zymogens?

    <p>They hold the structure together even after proteolytic cleavage.</p> Signup and view all the answers

    Which statement accurately describes the interaction of fibrin monomers in clot formation?

    <p>The overlapping of fibrin monomers creates fibers with distinct sizes.</p> Signup and view all the answers

    In the context of blood clotting, what is the significance of the proteolytic activation cascade?

    <p>It regulates the sequential activation of proteases, leading to fibrin formation.</p> Signup and view all the answers

    How does the T state of an allosteric enzyme compare to the R state in terms of KM?

    <p>The T state has a higher KM than the R state.</p> Signup and view all the answers

    What effect do activators have on the allosteric enzyme system?

    <p>They shift the system toward the R state.</p> Signup and view all the answers

    In the context of pyrimidine synthesis, which step is considered the first committed step?

    <p>Formation of N-carbamoyl-L-aspartate from carbamoyl phosphate and aspartate.</p> Signup and view all the answers

    What is the role of ATP in the regulation of ATCase?

    <p>ATP is an activator of ATCase.</p> Signup and view all the answers

    What characterizes the v vs. [S] curve of an allosteric enzyme in the absence of effectors?

    <p>It is sigmoidal.</p> Signup and view all the answers

    Which statement accurately describes the effect of extreme positive cooperativity in substrate binding?

    <p>The enzyme is inactive below a certain substrate concentration.</p> Signup and view all the answers

    How are the regulatory and catalytic subunits of ATCase organized?

    <p>The regulatory subunits lie on the outer surfaces and control the catalytic subunits.</p> Signup and view all the answers

    What is the effect of CTP on ATCase activity?

    <p>CTP acts as an inhibitor.</p> Signup and view all the answers

    What does the term 'induced fit' imply in the context of enzyme catalysis?

    <p>The unbound enzyme exhibits conformational homogeneity.</p> Signup and view all the answers

    Which equation represents the relationship of reaction velocity to the concentration of the enzyme-substrate complex?

    <p>$v = kcat[ES]$</p> Signup and view all the answers

    What principle is applied when substrate binding alters the conformational equilibrium of the unbound enzyme?

    <p>Le Chatelier’s principle</p> Signup and view all the answers

    Under what condition does the assumption of equilibrium between E, S, and ES hold true?

    <p>When the reaction is initiated by mixing enzymes and substrates.</p> Signup and view all the answers

    What is the significance of the steady state in enzyme kinetics?

    <p>It shows that the concentration of ES remains constant.</p> Signup and view all the answers

    Which statement is true regarding the simplification of the rate equation for enzyme-catalyzed reactions?

    <p>It relies on the assumption that k1, k-1, and k3 are much larger than k2.</p> Signup and view all the answers

    What do cofactors, vitamins, and essential metals contribute to enzyme activity?

    <p>They stabilize the enzyme structure and function.</p> Signup and view all the answers

    What characterizes the process of conformational selection in enzyme-substrate interactions?

    <p>Substrate binds preferentially to the pre-existing conformation of the enzyme.</p> Signup and view all the answers

    Study Notes

    Biochemistry I - CHM219

    • Course taught by Assist. Prof. Dr. Esra Aydemir
    • Focuses on Enzymes, their kinetics, and regulation
    • Includes topics on the kinetics of enzymatic catalysis, enzyme inhibition, cofactors, vitamins, essential metals, non-protein biocatalysts (catalytic nucleic acids), allosteric enzymes, covalent modifications, multisubstrate reactions, and more.

    Enzyme Kinetics

    • Enzymes are biological catalysts
    • The Michaelis-Menten equation relates initial reaction rate (Vo), maximum reaction rate (Vmax), and substrate concentration ([S]) through the Michaelis constant (KM)
    • KM is a measure of substrate-binding affinity.
    • The steady-state assumption proposes that the concentration of the enzyme-substrate complex (ES) remains nearly constant during most of the reaction
    • Vmax is approached asymptotically as [S] increases
    • To analyze the initial rate, assumes k1, k-1, and k3 are >> k2
    • Equation simplifies to Vo = (kcat[E]T[S])/(KM + [S])
    • kcat is the apparent rate constant for the rate-determining conversion of substrate to product
    • [ES] is difficult to measure experimentally
    • Vo = kcat[ES]

    Enzyme Inhibition

    • Enzyme inhibition can be reversible or irreversible
    • Competitive inhibitors compete with the substrate for the active site
    • Competitive inhibitors increase the apparent KM but do not affect Vmax
    • Uncompetitive inhibitors bind only to the enzyme-substrate complex (ES)
    • Uncompetitive inhibitors decrease both apparent Vmax and apparent KM
    • Mixed inhibitors bind to both the enzyme and the enzyme-substrate complex (ES)
    • Different effects on KM and Vmax depending on the inhibitor's affinity for each form.

    Cofactors, Vitamins, and Essential Metals

    • Many essential vitamins are constituents of enzyme cofactors
    • Cofactors are non-protein components that are essential for the catalytic function of some enzymes
    • Essential metals such as Zn, Fe, Cu, Co, Mo, V, Se, Mg are important cofactors
    • Examples were given, such as of reaction involving NAD/NADH, and other cofactors related to vitamins.

    Nonprotein Biocatalysts: Catalytic Nucleic Acids

    • Ribozymes (catalytic RNA) are a class of ribonucleic acids that also function as biological catalysts.
    • The production of tRNA from pre-tRNA is catalyzed by a ribonucleases P complex.
    • The RNA portion of ribonuclease P can catalyze the hydrolysis of the specified phosphodiester bond.

    Regulation of Enzyme Activity: Allosteric Enzymes

    • Regulation of enzyme activity is essential for efficient and ordered flow of metabolism
    • Feedback control is important in regulating complex metabolic pathways
    • Allosteric enzymes show cooperative substrate binding
    • Allosteric enzymes can be activated or inhibited by effectors (e.g., ATP, CTP)

    Covalent Modifications

    • Phosphorylation and dephosphorylation are examples of reversible covalent modification.
    • The enzymes that carry out these modifications (kinases/phosphatases) are regulated by ATP/ADP
    • Other covalent modifications include adenylylation, acetylation, and ADP-ribosylation

    Zymogens

    • Some enzymes are activated by proteolytic cleavage after initial synthesis as zymogens.
    • Examples include pancreatic proteases (trypsinogen, chymotrypsinogen)

    Blood Clotting

    • Blood clotting involves a cascade of proteolytic activations of specific proteases
    • Each factor can exist in an inactive or active form involved in this cascade.
    • The cascade can start from exposure to damaged tissue surfaces (extrinsic) or internal trauma to blood vessels (intrinsic).
    • The common result is activation of fibrinogen to form clotting fibrin.

    Multisubstrate Reactions

    • Multisubstrate reactions are categorized by the order of substrate binding (Random, Ordered, Ping-Pong).

    Lineweaver-Burk plot, Eadie-Hofstee Plots

    • These linear plots are commonly used for analysis of enzymatic kinetics
    • These plots can be used to confirm a number of different kinetic behaviours.
    • Useful plots to determine important kinetic variables (Vmax and KM).

    Other

    • The notes contain diagrams and tables to illustrate enzyme mechanisms and examples of enzyme function
    • Contains information on enzyme kinetics, inhibition, cofactors, catalysis, regulation mechanisms, and various enzymes from example examples including ribonuclease and chymotrypsin.

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    Biochemistry I CHM219 Lecture Notes PDF

    Description

    This quiz covers the essential concepts of enzyme kinetics as presented in Biochemistry I. It includes discussions on the Michaelis-Menten equation, enzyme-inhibitor interactions, and the importance of cofactors and vitamins in enzymatic reactions. Test your understanding of enzyme behavior and their regulation!

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