Enzyme Action Models Quiz
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What does the 'Lock and Key' model of enzyme action describe?

  • Substrates fit into the 3-D structure of the enzyme's active site. (correct)
  • Enzymes change shape after substrate binding.
  • Substrates cause enzymes to form covalent bonds with each other.
  • Enzymes only work with specific substrates under extreme conditions.

    • Which aspect of the 'Induced Fit' model distinguishes it from the 'Lock and Key' model?

  • The active site remains unchanged until the reaction is complete.
  • Weak chemical bonds are not involved in substrate binding.
  • Enzymes catalyze a reaction without any substrates.
  • The enzyme changes shape after substrate binding for a better fit. (correct)

    • What type of bonds are formed between the enzyme and substrate according to the 'Lock and Key' model?

  • Covalent bonds only
  • Weak chemical bonds (correct)
  • Hydrogen bonds exclusively
  • Ionic bonds only

    • In the 'Induced Fit' model, what is the primary result of the substrate binding?

    <p>Conformational change brings chemical groups in position to catalyze reactions.</p> Signup and view all the answers

    How is the 'Induced Fit' model considered more accurate compared to the 'Lock and Key' model?

    <p>It accounts for dynamic changes in the enzyme's structure during substrate binding.</p> Signup and view all the answers

    What is the term for the complete, catalytically active enzyme with its bound coenzyme and/or metal ion?

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

    Which of the following best describes coenzymes?

    <p>Organic cofactors that are loosely bound and easily released</p> Signup and view all the answers

    What role do coenzymes typically play in enzymatic reactions?

    <p>Functioning as co-substrates or carriers of functional groups</p> Signup and view all the answers

    Which one of the following is NOT an example of a coenzyme?

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

    What suffix is commonly added to the name of an enzyme derived from its substrate?

    <p>-ase</p> Signup and view all the answers

    Why are enzymes crucial for biochemical reactions in the body?

    <p>They speed up chemical reactions that are otherwise too slow</p> Signup and view all the answers

    Which class of enzymes is responsible for oxidation-reduction reactions?

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

    What is the protein part of an enzyme called when it is not associated with its cofactor?

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

    What is the primary function of enzymes in biological processes?

    <p>Catalyze chemical reactions</p> Signup and view all the answers

    Which vitamin is NOT associated with a coenzyme mentioned in the content?

    <p>Thiamine (B1)</p> Signup and view all the answers

    Which of the following correctly describes the general structure of most enzymes?

    <p>Globular proteins</p> Signup and view all the answers

    What distinguishes prosthetic groups from coenzymes?

    <p>Prosthetic groups are tightly bound to enzymes</p> Signup and view all the answers

    Which type of enzyme inhibition is characterized by the inhibitor binding to the active site?

    <p>Competitive inhibition</p> Signup and view all the answers

    Which plot is commonly used to analyze enzyme kinetics?

    <p>Michaelis-Menten Plot</p> Signup and view all the answers

    What do enzymes require in order to catalyze reactions effectively?

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

    What is the significance of enzyme inhibition in medicine?

    <p>It can be used to regulate metabolic pathways.</p> Signup and view all the answers

    What role do cofactors play in enzymatic reactions?

    <p>They assist enzymes in catalyzing reactions but are not proteins.</p> Signup and view all the answers

    Which classification number indicates that hexokinase is a transferase?

    <p>2</p> Signup and view all the answers

    Which type of enzyme is involved in isomerization reactions?

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

    What is a common characteristic of enzyme structure?

    <p>Enzymes possess a globular shape and complex 3-D structure.</p> Signup and view all the answers

    Which of the following metals is NOT commonly noted as a metal ion cofactor?

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

    What is the function of the active site in an enzyme?

    <p>It determines which substrates can bind to the enzyme.</p> Signup and view all the answers

    Which of the following describes lyases?

    <p>They are involved in group elimination to form double bonds.</p> Signup and view all the answers

    What is the systematic name of hexokinase?

    <p>ATP:glucose phosphotransferase</p> Signup and view all the answers

    What happens to the reaction rate as enzyme concentration increases?

    <p>It levels off when substrate concentration is limiting.</p> Signup and view all the answers

    How does substrate concentration affect the reaction rate?

    <p>It increases until all enzyme active sites are engaged.</p> Signup and view all the answers

    What effect does a temperature increase beyond the optimum have on enzymes?

    <p>It causes enzyme denaturation and loss of function.</p> Signup and view all the answers

    What is the optimum temperature for human enzymes?

    <p>37°C</p> Signup and view all the answers

    How does pH affect enzyme function?

    <p>It can impact the charge of enzyme and substrate molecules.</p> Signup and view all the answers

    What occurs when the substrate concentration is extremely high?

    <p>All active sites become saturated, maximizing reaction rate.</p> Signup and view all the answers

    What is the typical optimum pH range for most human enzymes?

    <p>6-8</p> Signup and view all the answers

    What initial effect does increasing temperature have on enzyme-catalyzed reactions?

    <p>It increases the rate of molecular collisions.</p> Signup and view all the answers

    What is the main consequence of enzyme denaturation?

    <p>Loss of enzyme's 3D structure and functionality.</p> Signup and view all the answers

    What limits further increases in reaction rate when enzyme concentration is high?

    <p>Lack of available substrate.</p> Signup and view all the answers

    What pH range is optimal for the enzyme pepsin to function effectively?

    <p>pH 2-3</p> Signup and view all the answers

    Which change can lead to enzyme denaturation?

    <p>Extreme pH levels</p> Signup and view all the answers

    What is indicated by the term 'saturation effect' in enzyme kinetics?

    <p>Reaction velocity becomes constant due to a lack of available enzyme</p> Signup and view all the answers

    What does the Michaelis constant (KM) represent?

    <p>The substrate concentration at which the reaction proceeds at half maximal velocity</p> Signup and view all the answers

    In the Michaelis-Menten equation, what does Vmax represent?

    <p>Maximum reaction velocity at saturating concentrations of substrate</p> Signup and view all the answers

    What effect does extreme salinity have on enzyme function?

    <p>Causes enzyme denaturation</p> Signup and view all the answers

    Which plot is used to represent a linear transformation of the Michaelis-Menten equation?

    <p>Lineweaver-Burk Plot</p> Signup and view all the answers

    Which of the following describes the relationship between substrate concentration and reaction velocity in enzyme kinetics?

    <p>Proportional until saturation occurs</p> Signup and view all the answers

    How are the rates of formation and breakdown of the enzyme-substrate complex represented mathematically?

    <p>Rate of formation = k1[E][S], Rate of breakdown = (k-1 + k2)[ES]</p> Signup and view all the answers

    What type of graph exhibits a rectangular hyperbola in enzyme kinetics?

    <p>Plot of initial reaction velocity against substrate concentration</p> Signup and view all the answers

    Which statement best describes the role of cations and anions with respect to enzyme activity?

    <p>Changes in their concentrations can affect enzyme activity and denaturation.</p> Signup and view all the answers

    At which point does an enzyme reach saturation with its substrate according to Michaelis-Menten kinetics?

    <p>When further increases in substrate concentration do not increase reaction velocity</p> Signup and view all the answers

    How would an increase in pH beyond optimal levels likely affect trypsin activity?

    <p>It would cause denaturation and decreased activity</p> Signup and view all the answers

    Study Notes

    Lecture Outline

    • Enzymes are specialized, catalytically active biological macromolecules.
    • They act as specific, efficient catalysts for chemical reactions in aqueous solution.
    • Most enzymes are globular proteins; some are RNA (e.g., ribozymes and ribosomal RNA).

    Enzyme Naming and Classification

    • Enzymes are named by adding the suffix "-ase" to the name of their substrate or a description of their catalytic action.
    • Classified based on the type of reaction catalyzed.
      • Oxidoreductases: Oxidation-reduction reactions.
      • Transferases: Transfer of functional groups.
      • Hydrolases: Hydrolysis reactions.
      • Lyases: Group elimination to form double bonds.
      • Isomerases: Isomerization.
      • Ligases: Bond formation coupled with ATP hydrolysis.

    International Classification of Enzymes

    • Each enzyme is assigned a four-part classification number and a systematic name.
    • The systematic name identifies the reaction it catalyzes.
    • (Each class has subclasses further classifying the type of reaction.)

    Naming of Enzymes

    • Each enzyme has a formal name, often including the substrate and type of reaction.
    • Enzymes also have a systematic (EC) number, uniquely identifying the specific enzyme.

    Key Structure-Function Features of Enzymes

    • Enzymes are proteins.
    • They have a globular shape and complex 3D structure.
    • They have an active site with a specific shape and chemical environment to bind substrates.
    • Some enzymes require cofactors (metal ions or organic/metallo-organic molecules) to function properly.

    Enzyme Cofactors

    • Cofactors are helper molecules that increase enzyme function.
    • Metallic ions like Mg2+, Zn2+, Fe3+ assist in catalysis.
    • Coenzymes are organic cofactors readily released.
    • Prosthetic groups are tightly bound organic cofactors.

    Enzyme Cofactors (Metal Ion Cofactors)

    • Small inorganic ions (Mg2+, K+, Ca2+, Zn2+, Cu2+, Co, Fe) may be free or held in complexes within enzyme proteins.
    • Help with catalysis.

    Enzyme Cofactors (Organic/Metallo-organic Cofactors)

    • Coenzymes are organic molecules, easily released.
    • Prosthetic groups are organic molecules, tightly bound.
    • Many are derived from vitamins.
    • Examples include NAD (niacin, B3), FAD (riboflavin, B2), Coenzyme A.
    • Some coenzymes participate as co-substrates or as transient carriers (for functional groups).
    • Coenzymes may be helpful for transferring or acting on specific parts of a reactant molecule.

    Enzyme & Cofactors

    • Holoenzyme: The complete, catalytically active enzyme with bound cofactors and/or metal ions.
    • Apoenzyme/apoprotein: The protein portion of the enzyme (before the cofactor is added).

    Why Are Enzymes Important?

    • Enzymes catalyze biochemical reactions in the body by speeding them up.
    • Most biochemical and physiological reactions proceed at very slow paces without enzymes.

    Enzymes & Cellular Metabolism

    • Anabolism is the building of complex molecules from simpler ones via bond formation.
    • Catabolism is the breakdown of complex molecules into simpler ones via bond breaking.
    • Both anabolic and catabolic reactions require energy expenditure/release, and are tightly regulated by enzymes.

    Enzymes & Cellular Metabolism(Anabolism)

    • Enzymes create complex molecules through biosynthetic reactions, involving dehydration synthesis.
    • Anabolic reactions generally consume more energy than they release.

    Enzymes & Cellular Metabolism(Catabolism)

    • Enzymes break down complex molecules into simpler ones, requiring hydrolytic reactions (use of water).
    • Catabolic reactions generally produce more energy than they consume.

    Cellular metabolism

    • Catabolic reactions transform complex molecules to simpler ones, converting energy into usable forms like ATP.
    • Anabolic reactions take small molecules and build them into large ones, while consuming energy.

    Enzyme-catalyzed Metabolic Reactions

    • Enzymes speed up metabolic reactions by lowering activation energy (EA).
    • Enzymes provide an alternative pathway for reactions to occur.
    • Enzymes transiently bind to a substrate, and then releases it as products once the reaction is complete.

    How Do Enzymes Work?

    • Enzymes act as catalysts to speed up reactions without being consumed or chemically altered.
    • Enzymes accelerate the reaction rate.
    • The shape of the active site slightly changes to bind the substrate, (induced fit).

    Enzyme Action (Lock and Key/Induced Fit)

    • The Lock and Key model is a simpler representation.
    • The induced fit model is more accurate, as the active site changes shape to accommodate the substrate, forming a more precise, tight fit.

    Enzyme-catalyzed Metabolic Reactions

    • Graphs illustrate enzyme activity (rate or velocity) in the presence of different substrate concentrations.
    • Maximum reaction velocity(Vmax) is reached when all active sites are occupied, and addition substrate doesn't lead to a higher reaction rate.
    • The Michaelis constant (KM)—the substrate concentration when velocity is half of Vmax—indicates an enzyme's affinity for its substrate; lower KM = higher affinity.

    Factors Affecting Enzyme Function

    • Enzyme concentration, substrate concentration, temperature, pH, and salinity influence the rate of enzyme-catalyzed reactions.

    Factors Affecting Enzyme Activity (Enzyme Concentration)

    • Increasing enzyme concentration leads to a faster reaction rate, up to a certain point where all active sites for the reaction are bound.

    Factors Affecting Enzyme Activity (Substrate Concentration)

    • Increasing substrate concentration increases reaction rate until all active sites are occupied, resulting in the maximum sustainable rate, Vmax.

    Factors Affecting Enzyme Activity (Temperature)

    • Increasing temperature initially enhances the reaction rate due to more collisions but excessively high temperatures lead to enzyme denaturation which decreases activity.

    Factors Affecting Enzyme Activity (Optimum Temperature)

    • The optimal temperature for enzyme function where it is most effective at catalyzing reactions, due to the maximum possible amount of collisions between the enzyme and substrate.

    Factors Affecting Enzyme Activity (pH)

    • Each enzyme has an optimal pH range; extremes can negatively affect enzyme function by denaturation, or disrupting the charge of amino acid residues within the active site.

    Factors Affecting Enzyme Activity (Salinity)

    • Changes in salinity, causing an increase or decrease in ions affect enzyme function. Extreme salinity disruptions between charged amino acids within the enzyme and affects its 3D structure leading to denaturation.

    Enzyme Kinetics

    • Enzyme kinetics studies the rates of enzyme-catalyzed reactions to understand mechanisms through which activity is controlled.
    • Michaelis-Menten kinetics explain relationships between substrate concentration, reaction velocity, and enzyme activity.

    Michaelis-Menten Kinetics

    • All enzymes display a saturation effect with their substrate(s).
    • At low substrate concentrations, velocity (V) is proportional to substrate concentration.
    • At high substrate concentrations, velocity plateaus and becomes independent of substrate concentration.

    Michaelis-Menten Kinetics

    • Initial reaction velocities(V0) against substrate concentration([S]) display a rectangular hyperbola shape.
    • Derived equations use kinetics models and explain the saturation effect for enzyme activity.

    Michaelis-Menten Kinetics

    • Michaelis-Menten model and scheme postulates how enzymes bind substrates, and undergoes catalytic reactions and/or reverses back to its original form.

    Graphical Determination of the Inhibitor Constant (Ki)

    Significance of KM (Michaelis Constant)

    • Lower KM values, the greater the affinity of an enzyme for its substrate, as evident through faster and more efficient reactions, with lower substrate concentrations.

    Significance of Vmax

    • Vmax indicates the maximum catalytic rate of an enzyme under optimal conditions.
    • Higher Vmax correlates to a greater reaction rate; or efficiency at which the substrate is converted into products.

    Enzyme Inhibition

    • The activity of enzymes (or their efficiency in catalyzing reactions) must be regulated.
    • Enzyme inhibition is a mechanism for regulating and controlling the activity.

    Types of Enzyme Inhibition

    • Two types are irreversible and reversible.
    • Reversible inhibition can be competitive, non-competitive, or uncompetitive in nature.

    Types of Enzyme Inhibition-Competitive

    • Competitive inhibition happens when an inhibitor competes with the substrate for binding to the active site on the enzyme.
    • The presence of excess substrate can shift the balance in favor of substrate binding to the active site, effectively reversing the inhibition.

    Types of Enzyme Inhibition- Non-Competitive

    • Non-competitive inhibition occurs when the inhibitor binds to a separate site on the enzyme other than the enzyme's active site, which alters the active site structure that affects or preventing the binding of substrate(s).
    • Substrate cannot bind to the altered active site.

    Types of Enzyme Inhibition- Uncompetitive

    • Uncompetitive inhibition takes place when the inhibitor binds only to the enzyme-substrate complex, preventing the formation of the product.
    • The binding of the inhibitor decreases both apparent KM and Vmax values.

    Summary of the Effect of Enzyme Inhibition on the KM and Vmax

    • Each type of enzyme inhibition results in distinct effects on apparent KM and/or Vmax, providing a mechanism for regulating enzyme activity.

    Inhibitors Constant (Ki)

    • Ki is a measure of how tightly an inhibitor binds to the enzyme, enabling comparison and classification.

    Enzymes as Important Drug Targets

    • Enzymes are potential targets for drugs; inhibitors can be used to treat various diseases.

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    Description

    Test your knowledge on the 'Lock and Key' and 'Induced Fit' models of enzyme action. This quiz covers important concepts such as coenzymes, enzyme-substrate interactions, and the significance of enzymes in biochemical reactions. Perfect for biochemistry students seeking to deepen their understanding of enzyme function.

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