Unit 2 Section 3.2 Factors Affecting Enzyme Activity

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  • Factors Affecting Enzyme Activity
    • Temperature
      • More heat means more kinetic energy, so molecules move faster
      • more heat makes it more likely that the substrate molecules collide with the enzyme's activity
        • the energy of these colluons also increases which means each collision is more likely to result in a reaction
          • the rate of reaction continues to increase until the enzyme reaches its optimum temperature - this is the temperature at which the rate  of an enzyme controlled reaction at its fastest
            • if the temperature gets too high, the reaction stops. the rise in temperature makes the enzyme's molecules vibrate more.
              • if the temperature goes above a certain temp, this vibration breaks some of the bonds that hold the enzyme in shape
                • the active site changes shape and the enzyme and substrate no longer fit together, at this point the enzyme is denatured - it no longer functions as a catalyst
    • pH
      • All enzymes have an optimum pH value
        • this is the pH at which the rate of an enzyme controlled reaction is at its fastest
          • most human enzymes work best at pH 7 (neutral) but there are exceptions - Pepsin works best at acidic pH 2
            • above an below the optimum pH, the H +  and OH- ions found in acids and alkalis can break the ionic bonds and hydrogen bonds that hold the enzyme;s tertiary structure in place
              • this makes the enzyme's active site change shape, so the enzyme is denatured
    • Enzyme Concentration
      • the more enzyme molecules there are in a solution, the more likely a substrate molecule is to collide with one and form an enzyme increases the rate of reaction
        • but if the amount of substrate is limited, there comes a point when there's more than enought enzyme molecules to deal with all the available substrate, so adding more enzyme has no further effect
    • Substrate Concentration
      • the higher the substrate concentration, the faster the reaction.
        • More Substrate molecules means a collision between substrate and enzyme is more likely, so more active sites will be used and more enzyme - substrate complexes will be formed
          • this is only true up until a 'saturation point though. after that there are so many substrate molecules that enzymes have about as much as they can cope with, and adding more makes no difference - the enzyme concentrayion becomes the limiting factor
    • Mesuring the rate of an enzyme controlled reaction
      • 1) You can measure how fast the product of the reaction appears and use this to compare the rate of reaction under different conditions
      • 2) You can also measure the disappearance of the substrate over time and use this to compare the rate of reaction under different conditions


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