1213 Week 19 T

Enzyme Catalysed Reactions
1. E + S <-> ES <-> E + P
2. the relationship between time and product formed is exponential
3. as time goes on the rate of reaction slows
  1. concentration of the substrate decreases over time so there are less collisions
  2. velocity of the back reaction increases
  3. product may inhibit the enzyme
  4. enzyme may be labile
4. concentration against initial reaction rate is hyperbolic
5. Vmax = maximum reaction rate
6. Km = concentration of substrate where half of the enzyme active sites are occupied (half Vmax) (conc units)
7. Michaelis-Menten equation is velocity=Vmax[S] / ([S] + Km)
8. if the substrate dissociates quicker than the rate of product formation Km becomes the substrate dissociation constant
  1. if this occurs then the smaller Km the higher the affinity of the substrate to the enzyme
9. it is difficult to measure Vmax because there is poor solubility of substrate at high concentrations
10. the Lineweaver-Burk plot removes the issue of insolubility
  1. on the plot
    1. y axis = 1/v
    2. x axis = 1/[S]
    3. the slope = Km/Vmax
    4. the intercept = 1/Vmax
Allosteric Enzymes
1. allosteric - the binding site for the effector molecule is not the active site of the substrate
2. co-operative binding = occurs if the number of binding sites of a molecule that are occupied by a specific type of ligand is a non-linear function of this ligand's concentration
3. cooperative binding produces a sigmoidal graph of initital reaction rate against substrate concentration
4. mechanisms that control enzyme activity
  1. feedback inhibition by a product
  2. gene expression - amount of enzyme altered
  3. phosphorylation/dephosphorylation
  4. proteolysis - irreversible activation and altering life span through changes in rate of enzyme degradation
Inhibition of Enzyme Activity
1. irreversible inhibitors
  1. form a covalent or they bind too tightly so dissociation is extremely slow
  2. enzyme activity can only be restored by synthesis of new enzymes
2. reversible inhibitors
  1. competitive
    1. have a similar shape too the substrate
    2. bind to the active site
    3. can be overcome by increasing the substrate concentration
    4. alter the slope of the Lineweaver-Burk plot but not the y axis intercept
    5. Vmax remains the same
    6. Km changes
  2. non-competitive
    1. bind to a site different to the active site of the substrate
    2. can not be overcome by increasing substrate concentration
    3. decrease the efficiency of the enzyme rather than stopping the reaction
    4. Vmax changes
    5. Km doesn't change
    6. alter the slope of the Lineweaver-Burk plot but not the x axis intercept
3. organophosphates
  1. target enzyme - acetylcholinesterase
  2. uses - chemical warfare, insecticides
  3. physiological effects
    1. nerve agents
    2. produce a cholinergic toxidrome as a result of excessive activation of the PSNS
    3. DUMBBELS
      1. D - diarrhoea
      2. U - urination
      3. M - miosis
      4. B - bronchorrhoea
      5. B - bronchospasm
      6. E - emesis
      7. L - lacrimation
      8. S - salivation

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1213 Week 19 T

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