Enzymes: Functions, Types, and Characteristics
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Questions and Answers

What is the main function of cofactors in enzyme activity?

  • To cleave bonds by adding water
  • To activate proenzymes
  • To increase the activation energy of a reaction
  • To help apoenzymes become holoenzymes (correct)
  • Where are extracellular enzymes found?

  • In the gastrointestinal tract, blood, and extracellular matrix (correct)
  • In the nucleus of cells
  • Only in the extracellular matrix
  • In the cytoplasm of cells
  • What is the function of the active site in an enzyme?

  • To bind the substrate and lower the activation energy (correct)
  • To increase the activation energy of a reaction
  • To cleave bonds by adding water
  • To transfer electrons between molecules
  • What type of enzymes transfer electrons between molecules?

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

    What is the purpose of compartmentalizing enzymes into organelles within cells?

    <p>To separate specific biochemical pathways</p> Signup and view all the answers

    What type of enzymes break chemical bonds without hydrolysis or oxidation-reduction?

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

    What is the function of acetylcholinesterase, a plasma membrane enzyme?

    <p>To degrade extracellular neurotransmitters</p> Signup and view all the answers

    What is the shape of the reaction velocity curve with increasing substrate concentration?

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

    Which of the following is NOT a characteristic of enzymes?

    <p>They are consumed during reactions.</p> Signup and view all the answers

    Isoenzymes differ from regular enzymes in that they:

    <p>Are encoded by different genes, resulting in slight structural variations.</p> Signup and view all the answers

    Which of the following statements is TRUE about proenzymes?

    <p>They are inactive forms of enzymes that are activated by proteolytic cleavage.</p> Signup and view all the answers

    How do cofactors assist enzymes in catalyzing reactions?

    <p>They bind to the active site and directly participate in the reaction.</p> Signup and view all the answers

    Why are enzymes compartmentalized within cells?

    <p>All of the above.</p> Signup and view all the answers

    Which of the following is NOT a function of extracellular enzymes?

    <p>Regulating gene expression.</p> Signup and view all the answers

    What type of enzyme inhibitors bind to the active site of an enzyme and compete with the substrate for binding?

    <p>Competitive inhibitors.</p> Signup and view all the answers

    Which of the following is NOT a mechanism of enzyme activity regulation?

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

    Study Notes

    Characteristics of Enzymes

    • Enzymes are catalysts that are not consumed in reactions
    • They are mainly proteins, highly specific, and interact with substrates

    Isoenzymes

    • Isoenzymes are different enzymes that catalyze the same reaction but are produced by different tissues
    • Example: hexokinase/glucokinase

    Proenzymes

    • Proenzymes (or zymogens) are inactive enzymes with extra protein sequences
    • They are activated by cutting off the extra protein sequence
    • Mainly found as extracellular enzymes, e.g. digestive proteases

    Cofactors

    • Cofactors help apoenzymes become holoenzymes
    • Types of cofactors:
      • Metal ions that can bind substrates
      • Small organic molecules (coenzymes) derived from vitamins
    • Cofactors participate in oxidation and reduction reactions

    Enzyme Compartmentalization

    • Enzymes are found intracellularly, compartmentalized into their organelles
    • This separates specific biochemical pathways

    Extracellular Enzymes

    • Found in:
      • Gastrointestinal tract (to digest dietary macromolecules)
      • Blood (to mediate blood clot formation)
      • Extracellular matrix (for remodeling during normal tissue turnover and tissue injury)

    Plasma Membrane Enzymes

    • Sit inside the cell membrane
    • Examples:
      • Acetylcholinesterase degrades extracellular neurotransmitters
      • Cyclooxygenases produce inflammatory mediators

    Enzyme Catalysis

    • The active site allows for catalytic activity due to its cofactors and amino acid side chains that bind the substrate
    • Enzymes lower activation energy, and the binding of substrate to enzyme further lowers activation energy to make the reaction easier

    Classes of Enzymes

      1. Oxidoreductases: transfer electrons between molecules
      1. Transferases: transfer functional groups
      1. Hydrolases: cleave bonds by adding water
      1. Lyases: break chemical bonds (not by hydrolysis or oxidation-reduction)
      1. Isomerases: rearrange molecule structure
      1. Ligases: form bonds between two large molecules

    Enzyme Kinetics

    • Reaction velocity shows saturation kinetics with increasing substrate concentration (hyperbolic curve)

    Allosteric Enzymes

    • Allosteric enzymes differ from regular enzymes in their regulation

    Environmental Factors Affecting Enzyme Function

    • Various environmental factors affect enzyme function

    Michaelis-Menten Kinetics

    • Vmax and Km represent the maximum reaction rate and the substrate concentration at which the reaction rate is half of Vmax, respectively

    Lineweaver Burk Plot

    • Provides information about substrate binding affinity and maximum reaction rate

    Enzyme Inhibitors

    • Irreversible enzyme inhibitors: covalently bind to enzymes, permanently inactivating them
    • Reversible enzyme inhibitors: bind non-covalently to enzymes, reducing their activity
    • Examples of competitive inhibitors: succinate and malonate
    • Noncompetitive inhibitors affect enzyme kinetics differently than competitive inhibitors

    Mechanisms of Enzyme Activity Regulation

    • Proenzymes typically activated by cutting off extra protein sequences
    • Allosteric effectors influence enzyme activity
    • Feedback inhibition regulates enzyme activity
    • Phosphorylation and dephosphorylation regulate enzyme activity

    Diagnostics

    • Creatine Phosphokinase is used in diagnosing heart attacks
    • Enzyme levels change during tissue or organ damage
    • Different tissues produce different versions of enzymes that catalyze the same reaction

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    Description

    This quiz covers the key characteristics of enzymes, types of enzymes, and their functions in the cell. It also explores how enzymes catalyze reactions, cofactors, and more.

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