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Cell Biology: Bioenergetics and Enzymes

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Termini in questo insieme (20)

  • What types of work do cells perform that require energy?
    Cells perform mechanical work, transport work, and chemical work, all requiring energy input.
  • What is bioenergetics?
    Bioenergetics is the application of thermodynamic principles to biological systems, focusing on energy conservation and transformation.
  • What does it mean that cells are an open system?
    Cells exchange energy and matter with their surroundings, allowing them to maintain order and perform work.
  • What is the difference between a calorie and a Calorie on food labels?
    A calorie (small c) is the energy to raise 1g of water by 1°C; a Calorie (capital C) equals 1000 calories or 1 kilocalorie.
  • What determines the direction of chemical reactions in cells?
    The entropy of the universe must increase (2nd law of thermodynamics) and the free energy of the system must decrease.
  • What does a negative free energy change (ΔG) indicate about a reaction?
    A negative ΔG means the reaction is exergonic and proceeds spontaneously in the forward direction.
  • What is the difference between ΔG' and ΔG0'?
    ΔG0' is the standard free energy change under standard conditions; ΔG' is the actual free energy change under cellular conditions.
  • Define exergonic and endergonic reactions.
    Exergonic reactions release energy (ΔG < 0); endergonic reactions require energy input (ΔG > 0).
  • What does 'steady state' mean in cellular reactions?
    Steady state means reactant and product concentrations remain constant over time despite ongoing reactions.
  • How can reactions with positive ΔG' values proceed in cells?
    By altering reactant/product ratios or coupling the reaction to a highly exergonic reaction.
  • Define enzyme, substrate, and active site.
    An enzyme is a protein catalyst; substrate is the molecule acted upon; active site is the enzyme region where substrate binds.
  • What is an allosteric site on an enzyme?
    An allosteric site is a regulatory site where molecules bind to modulate enzyme activity.
  • What is turnover number (kcat)?
    kcat is the number of substrate molecules converted to product per enzyme molecule per second.
  • Define KM and Vmax in enzyme kinetics.
    KM is the substrate concentration at half Vmax; Vmax is the maximum reaction rate achieved by the enzyme.
  • How do enzymes affect activation energy (EA) and reaction rates?
    Enzymes lower EA, increasing reaction rates without changing ΔG.
  • What factors affect enzyme activity?
    pH, temperature, ion concentration, and presence of inhibitors affect enzyme structure and activity.
  • What is the difference between competitive and noncompetitive reversible inhibitors?
    Competitive inhibitors bind the active site; noncompetitive inhibitors bind elsewhere, altering enzyme function.
  • How is enzyme activity regulated in cells after synthesis?
    Via allosteric regulation, chemical modification (e.g., phosphorylation), proteolysis, and sequestration.
  • Name four major classes of enzymes.
    Oxidoreductases, transferases, isomerases, and hydrolases.
  • Why are enzymes important for cellular reactions?
    They allow reactions to proceed at useful rates by lowering activation energy and stabilizing the metastable state.