Biochemistry Enzymes Overview
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Questions and Answers

What is the primary function of a catalyst in a chemical reaction?

  • To decrease the reaction rate by binding to the substrate.
  • To be consumed in the reaction and become part of the product.
  • To increase the reaction rate without being permanently altered. (correct)
  • To shift the reaction's equilibrium towards the products.

    • In the context of an enzymatic reaction, what does the symbol ⇌ typically signify?

  • The reaction is reversible. (correct)
  • The reactants and products exist in equal concentrations.
  • The reaction only proceeds towards the products.
  • The reaction is irreversible.

    • Which of the following statements is true regarding the effect of enzymes on reaction equilibrium?

  • Enzymes shift the equilibrium to favor substrate formation.
  • Enzymes have no effect on the equilibrium position. (correct)
  • Enzymes increase the concentrations of both products and substrate.
  • Enzymes shift the equilibrium to favor product formation.

    • What does the term 'activation energy' refer to in the context of chemical reactions?

    <p>The energy required to start a chemical reaction. (B)</p> Signup and view all the answers

    How do enzymes affect the activation energy of a reaction?

    <p>They decrease the activation energy. (D)</p> Signup and view all the answers

    What is a 'substrate' in the context of an enzymatic reaction?

    <p>The molecule upon which the enzyme acts. (A)</p> Signup and view all the answers

    Which of the following best describes the transition state in an enzymatic reaction?

    <p>A highly unstable complex requiring high energy. (A)</p> Signup and view all the answers

    What is the typical optimal pH environment in which most human enzymes function?

    <p>7.4 (C)</p> Signup and view all the answers

    According to the content, what is the typical optimum temperature at which most human enzymes function?

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

    What are the catalytic RNA molecules called?

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

    What is the primary role of an enzyme in a chemical reaction?

    <p>To lower the activation energy of the reaction (B)</p> Signup and view all the answers

    Which of the following best describes a coenzyme?

    <p>A compound usually derived from a vitamin that assists an enzyme with catalysis (C)</p> Signup and view all the answers

    What is a holoenzyme?

    <p>The combination of an apoenzyme and a coenzyme (C)</p> Signup and view all the answers

    Which enzyme class is responsible for catalyzing the joining of two molecules?

    <p>Ligase (A)</p> Signup and view all the answers

    Which of the following enzymes has the largest rate enhancement between its catalysed and uncatalysed rate?

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

    An enzyme that facilitates the conversion of glucose-6-phosphate (G6P) to fructose-6-phosphate (F6P) belongs to which class?

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

    Which of these would be considered a cofactor?

    <p>Mg2+ (C)</p> Signup and view all the answers

    A reaction involving the breaking of a peptide bond in a protein is most likely catalyzed by which class of enzyme?

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

    Which of the following describes what happens to the equilibrium of a reaction when an enzyme is added?

    <p>The equilibrium remains unchanged (D)</p> Signup and view all the answers

    The reaction alcohols ⇌ aldehydes is likely catalyzed by which class of enzyme?

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

    Flashcards

    Activation Energy

    The minimum amount of energy required for a chemical reaction to occur. Enzymes lower this energy barrier, speeding up reactions.

    Coenzyme

    A compound derived from a vitamin that assists an enzyme in catalyzing a reaction.

    Cofactor

    An inorganic ion that assists an enzyme in catalyzing a reaction.

    Apoenzyme

    The protein-only portion of an enzyme that requires an additional coenzyme to function.

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    Holoenzyme

    The fully functional enzyme, consisting of the apoenzyme and its coenzyme.

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    Enzyme

    A protein (or sometimes RNA) that acts as a biological catalyst, speeding up specific biochemical reactions without being consumed in the process.

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    Reaction Rate

    A measure of how fast a reaction proceeds. It's the number of reactant molecules converted to product molecules per unit of time.

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    Half-life

    The time it takes for half of the reactant molecules to be converted to product molecules. It's a way to measure how fast a reaction is.

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    Oxidoreductase

    A class of enzymes that catalyze reactions involving the transfer of electrons or hydrogen atoms.

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    Ligase

    Enzymes that catalyze the joining of two molecules together, often using ATP hydrolysis as an energy source.

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    Catalyst

    A substance that speeds up a chemical reaction without being consumed itself.

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    Substrate

    The molecule that an enzyme acts upon. It's the 'ingredient' being transformed by the enzyme.

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    Product

    The molecule produced as a result of an enzyme-catalyzed reaction. It's the new 'product' created.

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    Lowering Activation Energy

    The process by which enzymes lower activation energy by providing an alternative pathway for a reaction.

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    Transition State

    A highly unstable intermediate state that occurs during a reaction. It requires a lot of energy and is short-lived.

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    Equilibrium

    The state where the concentrations of substrate and product are balanced and unchanging in a closed system.

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    Enzyme Effect on Equilibrium

    Enzymes do not affect the final balance of products and substrates (equilibrium) but make the reaction happen much faster.

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    Study Notes

    • La Trobe University reproduced the material under the Copyright Act 1968 (part VB).
    • Any further reproduction is subject to copyright protection.
    • Do not remove the copyright notice.

    Enzyme Features and Classes

    • Enzymes are biological catalysts that increase reaction rates without being consumed.
    • They accelerate reactions by lowering the activation energy.
    • Enzymes are primarily proteins, although some are catalytic RNA molecules called ribozymes.
    • Enzymes operate optimally at pH 7.4 and 37°C (for most human enzymes).

    Intended Learning Outcomes

    • Students will understand enzymes as catalysts in biochemical reactions.
    • Students will identify basic enzyme features.
    • Students will describe the major enzyme classes.
    • Students will grasp that enzymes reduce activation energy but do not alter equilibrium.

    Enzymatic Equation

    • Enzymatic reactions follow the general equation: E + S ⇌ ES ⇌ EP ⇌ E + P,
    • Where E = enzyme, S = substrate, and P = product.
    • Substrate is the molecule the enzyme acts on.
    • Product is the molecule formed from the reaction.

    Reaction Rate vs. Equilibrium

    • Reaction rate measures substrate and product concentration change.
    • Equilibrium is where these concentrations no longer change in a closed system.
    • Equilibrium does not necessitate equal substrate and product concentrations.
    • Enzymatic equations usually use the reversible sign to signify reversibility of the reaction.

    Equilibrium in Simple Terms

    • At equilibrium, the system balances; no net change in substrate or product quantities.
    • Reactions still occur in both directions but their rates are equal.
    • Equilibrium denotes a dynamic state where reaction rates are equal in both directions.

    Enzymes Increase Reaction Rate

    • Enzymes do not change the amount of product formed at equilibrium.
    • Enzymes simply accelerate the time to reach equilibrium.

    Enzymes Lower Activation Energy

    • Enzymes lower activation energy in reactions using alternative routes.
    • This alternate route is represented by a lower activation energy peak on a reaction progress diagram.

    Changes in Transition State

    • Transition state without enzyme is highly unstable requiring high activation energy.
    • Transition state with enzyme is more stable, requiring less activation energy, through intermediate formation.

    Enzyme Rates

    • Enzymes dramatically increase reaction rates from billions to quadrillions of times faster in some cases.

    What Enzymes Need To Work

    • Some enzymes function without other compounds .
    • Some enzymes require coenzymes generated from vitamins (e.g. NADH) or cofactors to function.
    • Cofactors can alter enzyme conformation (shape) for better function (e.g. metal ions like Mg2+, Fe2+, Zn2+).

    Definitions

    • An enzyme acts as a catalyst, speeding up biochemical reactions.
    • Coenzymes are vitamin-derived molecules helping enzymes.
    • Cofactors are non-protein molecules (i.e. ions) aiding enzymes.
    • Apoenzyme is the protein component of an enzyme requiring coenzymes to finalize functionality.
    • Holoenzyme is the combination of apoenzyme and coenzyme for an active enzyme.

    Enzyme Classifications

    • There are six major enzyme classes based on the reaction they catalyze.
    • Examples of classes include oxidoreductases (alcohol dehydrogenase), transferases (kinases), hydrolases (lipases), lyases (decarboxylases), isomerases (isomerase), and ligases (DNA ligase).

    Summary

    • Enzymes increase reaction rates by decreasing activation energy.
    • Enzymes do not alter the equilibrium of the reaction.
    • Some need cofactors/coenzymes.
    • Enzymes are categorized into six classes.

    Resources

    • Lehninger Principles of Biochemistry (Seventh Edition, 2017) by Freeman and Company, specifically Chapter 6.

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    Related Documents

    Lecture 1 - Enzyme Features and Classes PDF

    Description

    This quiz covers the fundamental concepts of enzymes as biological catalysts in biochemical reactions. Participants will learn about enzyme features, classes, and their role in lowering activation energy. Test your understanding of the enzymatic equation and the optimal conditions for enzyme activity.

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