Enzymes

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  • Enzymes
    • Mechanism of Enzyme action
      • Induced Fit
        • Active site changes shape slightly when the substrate enters
        • initial interaction between  enzyme and substrate is week
        • Interactions rapidly induce changes in the enzymes tertiary structure
        • This can weaken a bond which will lower the Ea of the reaction
      • Lock and Key
        • Enzyme and substrate are complimentary in shape
        • Enzyme- substrate complex formed when substrate binds to active site
        • Enzyme-product complex formed after the substrate has reacted
        • R-groups of the active site will also interact with the substrate
    • Intracellular enzymes
      • Hydrogen Peroxide is a toxic product of many metabolic pathways.
        • Catalase ensures that it is broken down into oxygen and water quickly
    • Extracellular Enzymes
      • they can be used to break down polymers for nutritional purposes
        • this is done through digestion
      • Multicellular organisms need enzymes to digest and break down food
        • examples are: amylase and trypsin
      • Unicellular organisms need enzymes to break down  larger molecules so that they can be absorbed
    • Factors affecting enzymes
      • Temperature
        • Temperature coefficient Q10
        • Increasing the temperature of a reaction increases the kinetic energy of the particles
        • Denaturation- As temperature increases vibrations increase untuk the bonds strain and break completely.
          • this changes the tertiary structure of the protein. It is denatured.
        • Most bodily enzymes have an optimum temperature of around 40 degress.
          • Thermophilic bacteria have enzymes with much higher optimum temperatures
          • Psychrophilic organisms have enzymes with much lower optimum temperatures.
      • pH
        • The active site will only be the right shape at certain H+ concentration
      • Substrate and Enzyme concentration
        • Increasing the concentration of substrate, increases the collision frequency. More enzyme-substrate complexes are formed. The rate of reaction is faster
          • The same thing happens when the concentration of  the enzyme increases
        • Rate will continue to increase up to its Vmax.
    • Inhibition
      • Competitive
        • Inhibitor binds to the Active Site
        • Inhibitor is of similar shape to the substrate
        • Blocks substrate from entering the active site, prevents it catalysing the reaction
        • Reduces rate of reaction but does not change the Vmax.
        • Example: Statins are competitive inhibitors of cholesterol synthetics and are often prescribed to help reduce blood cholesterol levels
      • Non-competitive
        • Inhibitor binds to the allosteric sight
        • Causes the tertiary structure of the active sight to change, so its shape changes
          • Active site is no longer complimentary to substrate
        • Increasing the concentration of enzyme or substrate won't overcome its effect. Increasing the concentration of the inhibitor will further decrease the rate of reaction
        • Example: Organo-phosphates used as insecticides and herbicides irreversibly inhibit acetyl cholinesterase responsible for nervous transmission
      • End-product
        • The product of a reaction acts as n=an inhibitor for the enzyme that made it
        • Example of negative feedback
    • Cofactors and Coenzymes
      • Cofactors = non-protein 'helper,' components.
      • Coenzyme = A cofactor which is an organic molecule
      • Prosthetic groups are cofactors, they are required by certain enzymes to carry out their catalytic function.
      • Precursor Activation
        • precursor enzymes need to undergo a change in shape to be activated. the addition of a cofactor can do this
          • Before the cofactor is added the precursor protein is called an apoenzyme
          • After the cofactor is added it is called a holoenzyme

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