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Biochemistry: Enzyme Kinetics, Regulation, and Bioenergetics

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  • What is the role of enzymes in biochemical reactions?
    Enzymes speed up reactions by lowering the activation energy through substrate binding and catalysis.
  • Describe the Michaelis-Menten equation.
    Initial velocity vi = (Vmax [S]) / (Km + [S]), where Vmax is max velocity, Km is substrate concentration at half Vmax, and [S] is substrate concentration.
  • What does a low Km indicate about enzyme affinity?
    A low Km indicates high substrate affinity, meaning the enzyme reaches half-max velocity at low substrate concentration.
  • Explain the Lineweaver-Burk plot and its significance.
    A double-reciprocal plot of 1/vi vs 1/[S] used to determine Km and Vmax from the y-intercept (1/Vmax) and x-intercept (-1/Km).
  • What is the difference between hyperbolic and sigmoidal substrate saturation kinetics?
    Hyperbolic kinetics show simple saturation; sigmoidal kinetics indicate cooperative binding among enzyme subunits.
  • How does competitive inhibition affect enzyme kinetics?
    Competitive inhibitors bind the active site, increasing apparent Km but not changing Vmax; inhibition can be overcome by high substrate.
  • How does noncompetitive inhibition affect enzyme kinetics?
    Noncompetitive inhibitors bind allosteric sites, decreasing Vmax without changing Km; inhibition cannot be overcome by substrate.
  • What is feedback inhibition in metabolic pathways?
    End products inhibit enzymes earlier in the pathway to regulate metabolite flow and prevent overproduction.
  • Describe covalent modification of enzymes by phosphorylation.
    Kinases add phosphate groups to serine residues, altering enzyme activity; phosphatases remove them, reversing the effect.
  • What is the first law of thermodynamics in biological systems?
    Energy is conserved; it is transferred or transformed but not created or destroyed.
  • Define entropy and enthalpy in biochemical reactions.
    Entropy is system disorder; enthalpy is total heat content. Spontaneous reactions increase entropy and may release or absorb heat.
  • What does a negative ΔG indicate about a reaction?
    A negative ΔG means the reaction is exergonic and proceeds spontaneously, releasing free energy.
  • How is ATP used as an energy currency in cells?
    ATP stores energy in high-energy phosphate bonds and transfers it to drive endergonic reactions.
  • What is the role of the mitochondrial electron transport chain (ETC)?
    ETC transfers electrons from NADH/FADH2 to oxygen, pumping protons to create a gradient used for ATP synthesis.
  • Which ETC complexes pump protons and which do not?
    Complexes I, III, and IV pump protons; Complex II does not pump protons but transfers electrons from FADH2.
  • Explain the Q cycle in Complex III of the ETC.
    Q cycle splits two electrons from ubiquinol; one reduces cytochrome c, the other recycles ubiquinone, enhancing proton pumping.
  • What is the chemiosmotic theory?
    Electron transport pumps protons creating a gradient; ATP synthase uses proton flow back into the matrix to synthesize ATP.
  • How do uncouplers affect oxidative phosphorylation?
    Uncouplers dissipate the proton gradient, allowing electron transport without ATP synthesis, releasing energy as heat.
  • Describe the glycerol 3-phosphate shuttle.
    Transfers reducing equivalents from cytosolic NADH to mitochondrial FAD via glycerol 3-phosphate dehydrogenase.
  • Describe the malate-aspartate shuttle.
    Transfers reducing equivalents by converting oxaloacetate to malate in cytosol, transporting it into mitochondria, then back to oxaloacetate.