2.4 - enzymes

    Cards (23)

    • enzymes = 3D globular proteins that are biological catalysts, speeding up chemical reactions by lowering the activation energy
    • active site = the part of the enzyme that binds to the substrate and catalyses the reaction
    • substrate = the molecule that is changed into the product in a reaction
    • amino acids and R groups form a specific shape for a specific substrate
    • induced fit model = enzyme changes shape (conformational change) to fit the substrate and then reverts back
    • competitive inhibitors
      • have a shape similar to the active site
      • binds to the active site, preventing the substrate from entering
      • increasing the substrate concentration reduces the effect of the inhibitor
    • non competitive inhibitors
      • bind to the allosteric site ( not the active site)
      • causes a conformational change to the active site so the active site is no longer complementary to the substrate
      • increasing concentration has no effect on inhibition - max rate of reaction cannot be achieved
    • co factors = bind to the allosteric site
    • co enzymes = similar structure to the substrate, so they can bind to the active site
    • intracellular = inside the cell e.g. lysosomes
    • extracellular = outside the cell e.g. trypsin
    • enzyme + substrate >>> ES complex >>> enzyme + products
    • Apoenzyme (protein portion) + Cofactor = Holoenzyme
    • effect of temperature:
      • increasing temp = more kinetic energy, increasing the frequency of collisions, resulting in an increase in the number of E-S complexes and therefore an increase in the rate of the reaction and more product formation
      • temperature past optimum = reaction rate decreases rapidly as the enzyme denatures and stops working - hydrogen, disulfide and ionic bonds are broken
      • decreasing temp = rate of reaction decreases due to low kinetic energy meaning fewer ES complexes are formed -below freezing point, enzymes are inactivate
    • temperature coefficient (Q10)= measure of the rate of change of a biological or chemical system as a consequence of increasing the temperature by 10 °C.
    • Q10 = rate of reaction at (x + 10)°C / rate of reaction at x°C
    • rate of reaction = product/time
    • effect of pH
      • Most enzymes function efficiently over a narrow pH range
      • having a pH above or below the optimum pH of an enzyme, denatures the enzyme due to disruption to the hydrogen and ionic bonds
      • Most enzymes have an optimum pH of about 7.
      • Some enzymes function in acidic or alkaline pH – e.g. digestive enzymes
    • effect of substrate concentration
      • increasing substrate concentration increases collisions between S and E molecules occur more often
      • More ES complexes form – more product formed – reaction rate increases
      • Increasing substrate further – a point is reached where the rate reaches a maximum value
      • All the enzymes are forming ES complexes - all the active sites are occupied at all times
      • Any further increase in substrate will not have an effect on reaction rate because the enzyme concentration is the limiting factor
    • effect of enzyme concentration
      • As enzymes increase, more active sites become available
      • More ES complexes are formed - increase in reaction rate
      • If enzymes increased further – all the active sites will be occupied by S molecules
      • The rate is will eventually decrease as the substrate is the limiting factor
    • vitamins = organic co factors + co enzymes
    • minerals = inorganic co factors
    • allosteric site = a site on the enzyme that is not the active site
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