Enzymes OCR biology unit 2

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  • Enzymes
    • mode of action
      • globular proteins
        • have specific tertiary structure, coded by DNA
      • Biological Catalysts
        • speed up reactions without being used up.Metabolic reactions in body.
      • Active Site
        • attaches to complementary substrate.
      • Specific
        • only one substrate can bind to each active site
      • Substrate
        • molecule that is being broken down
      • Intracellular
        • Works inside cells
      • Extracellular
        • outside cell e.g heterotrophs
      • Activation Energy
        • energy needed to enable reaction to happen. Enzymes lower activation energy
      • Lock and Key
        • Active  site has complementary shape to substrate, substrate binds then the substrate is broken down and the products are released
      • Induced Fit
        • Substrate binds, active site changes slightly forming enzyme-substrate complex, causes strain on the molecule, reaction happens more easily forming enzyme-product complex, products no longer fit in active sire and are released.
    • Temperature
      • Increase
        • molecules have more kinetic energy which means the molecules move around faster, resulting in more successful collisions and increased rate of reaction
      • Increase above optimum
        • molecules vibrate which means the bonds vibrate and they eventually break, the tertiary structure is changed and the active site changes shape which means that the substrate is no longer complementary. This is denaturation.
      • Optimum
        • Temperature at which the enzyme has the fastest rate of reaction. This a balance between enough kinetic energy and vibration of bonds, this varies between organisms.
    • pH
      • More H+ means a lower pH which means it is more acidic.
      • H bonds between oppositely charged amino acids are needed to hold the tertiary structure in place
      • H+ can interfere with H bonds and ionic bonds. Therefore, change in H+ concentration can alter shape of active site, so change rate of reaction.
      • Optimum
        • pH at which  rate is highest, varies depending on environment enzyme is found in.
      • Buffer
        • Resists change in pH, therefore used to carry out reactions.
    • Concentrations
      • Substrate
        • Increase in  substrate concentration means that more molecules of substrate which increases collisions between enzyme and substrate which means there  is more enzyme-substrate complexes which means more product therefore showing an increased rate of reaction. maximum rate is eventually obtained as all enzymes are occupied at all times.
      • Enzyme
        • Increase in enzyme concentration means that more enzyme molecules are there so more active sites are available so there is more enzyme substrate complexes and the reaction rate increases, at some point, all substrate molecules are occupying active sites therefore it plateaus out unless more substrates are added.
    • Inhibitors
      • Competitive
      • Non Competitive
        • binds to allosteric site. Changes shape of active site meaning that the substrate is no longer complementary and cannot form the enzyme substrate complex.
    • Cofactors
      • Substrate that must be present for enzyme controlled reactions to happen at appropriate rate
        • Coenzymes, small, non-protein, organic. bind to active site for short time to enable reaction to happen. Often involved in and changed by, the reaction then recycled back. Often carry molecules to active site from another enzyme-link sequences of reactions together.
      • Prosthetic Groups. permanent part of the enzyme, contribute to final 3D shape and charge
      • Ions.Inorganic-presence can increase the rate of reaction, binding affects charge or shape so makes the making of the enzyme substrate complex to form more easily.
    • Poisons and drugs
      • Posions often inhibit or over activate enzymes
      • Drugs often inhibit enzymes


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