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Enzymes and Chemical Reactions in General Biology

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Terms in this set (20)

  • What is an enzyme?
    An enzyme is a macromolecule, usually a protein, that acts as a catalyst to speed up chemical reactions without being consumed.
  • What is activation energy?
    Activation energy is the energy needed to start a chemical reaction by getting molecules to the transition state where bonds can be broken.
  • Define Gibbs free energy (G).
    Gibbs free energy is the portion of a system's energy that can perform work when temperature and pressure are uniform, such as in living cells.
  • What characterizes an exergonic reaction?
    An exergonic reaction releases free energy (ΔG < 0), is spontaneous, and the reactants have more free energy than the products.
  • Give an example of an exergonic reaction.
    Cellular respiration: \(\mathrm{C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + energy}\).
  • What characterizes an endergonic reaction?
    An endergonic reaction absorbs free energy (ΔG > 0), is nonspontaneous, and the products have more free energy than the reactants.
  • Give an example of an endergonic reaction.
    Photosynthesis: \(\mathrm{6CO_2 + 6H_2O + energy \rightarrow C_6H_{12}O_6 + 6O_2}\).
  • How do enzymes affect activation energy and ΔG?
    Enzymes lower the activation energy of a reaction but do not change the overall ΔG or the spontaneity of the reaction.
  • What is the enzyme-substrate complex?
    It is the temporary complex formed when an enzyme binds to its substrate at the enzyme's active site.
  • What is the induced fit model?
    The enzyme undergoes a subtle change in shape after substrate binding to enhance the fit between enzyme and substrate.
  • List mechanisms by which enzymes lower activation energy.
    • Provide a template for substrate orientation
    • Stretch substrate bonds to weaken them
    • Create a favorable microenvironment
    • Participate directly in the reaction without being consumed
  • What factors affect the rate of an enzymatic reaction?
    Substrate concentration, enzyme concentration, and local conditions such as temperature and pH.
  • What are cofactors and coenzymes?
    Cofactors are non-protein helpers required for enzyme activity; organic cofactors are called coenzymes, e.g., vitamins.
  • Describe competitive inhibition.
    Competitive inhibitors reduce enzyme activity by binding to the active site, blocking substrate binding.
  • Describe noncompetitive inhibition.
    Noncompetitive inhibitors bind to a different site on the enzyme, changing its shape and reducing active site effectiveness.
  • What is allosteric regulation?
    Binding of a regulatory molecule at one site on an enzyme affects the enzyme's function at a different site, causing inhibition or stimulation.
  • Explain cooperativity in enzymes.
    A type of allosteric activation where substrate binding at one active site increases catalytic activity at other sites.
  • What is feedback inhibition?
    The end product of a metabolic pathway inhibits an enzyme within that pathway to regulate its own production.
  • Why is heat not an ideal way to speed up biological reactions?
    Heat can denature proteins and would accelerate all reactions indiscriminately, disrupting cellular function.
  • Can enzymes convert an endergonic reaction into an exergonic one?
    No, enzymes cannot change the overall free energy change or convert endergonic reactions into exergonic ones.