Core Concepts; Enzymes and Biological Reactions

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  • Enzymes & Biological Reactions
    • Protein Nature
      • reactions occur across metabolic pathways & include anabolic: build up; & catabolic: break down
      • Enzymes are
        • biological catalysts
        • tertiary proteins with specific shape from bonding
      • Sites of action
        • extracellular: secreted from cells
        • intracellular: in solution
        • membrane bound
    • Active Sites
      • reactions occur in an enzyme-substrate complex
      • Lock & Key
        • enzymes have specifically shaped active sites that can only catalyse one reaction
      • Induced Fit
        • shape altered by substrate binding, but returns to normal
    • Activation Energy
      • minimum energy needed for molecules to react & break reactant bonds to form new ones
      • More kinetic energy increases reaction rate as more successful collisions,
        • temperature increase kinetic energy
      • enzymes lower activation energy so reactions can occur at lower temps
    • Factors Affecting Enzymes
      • Temperature
        • increase kinetic energy as more successful collisiond
        • too high & vibrations break bonds so enzymes denatures
      • pH
        • small changes are reversible
        • big changes cause denaturing
      • Substrate conc
        • big conc increases rate as more possible reactions
        • at low conc, enzymes aren't working to full capacity
        • rate plateaus when enzymes are saturated
      • Enzyme conc
        • enzymes are reusable so low conc needed to catalyse many reactions
        • as increases, more collisions so faster rate of reaction
    • Enzyme Inhibition
      • Competitive
        • shape similar to substrate so competes for active site
        • makes collisions less likely but fixed by adding substrates
      • Non-competitive
        • bind at allosteric site & changes bonds & shape so substrate can't bind
        • non-reversible
    • Immobilsed Enzymes
      • when enzyme is fixed on an inert matrix e.g. sodium alginate beads
      • Benefits
        • non-contaminating
        • easy to recover and reuse
        • easy to purify
        • more stable as conditions change
      • used to make lactose free milk
        • fill beads with lactase which breaks lactose into glucose and galactose


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