BY1 Enzymes

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How an Enzyme Works

  • Enzyme active site- 3-12 amino acids
  • Active site is a shape whichis complementary to the shape of the substrate
  • Enzymes is specific to one type of substrate only
  • Random collision allow thesubstrate to enter the active site
  • forms temporary bonds with the enzyme
  • forms an enzyme-substrate complex
  • products are released
  • enzyme is unchanged and ready to act again
  • 'Lock and Key theory'
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Induced fit model

  • The active site of an enzyme is not perfectly complementary
  • Substrate enters the active site and forms the temporary bonds with the active site
  • this causes the active site to shape slightly
  • like a hand going into a glove
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How Enzyme concentration affects rate of reaction

  • Excess substrate and constant temperature and pH needed
  • rate of reaaction is proportional  tothe concentration of the enzyme
  • the more enzymes available, the more likely that a substrate will successfully collide with an active site
  • greater rate of reaction
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How substrate concentration affects rate of reacti

  • Enzyme concentrationand pH should be kept optimum
  • increasing  the substrate conecntration will increase the likelihood of successful collisions
  • therefore rate increases with increasing substrate concentration
  • there will be a point where further increase in subctrate concentration will have no affect because all of the enzyme active sites will be saturated.
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How temperature affects rate of reaction

  • molecules are heated
  • gain kinetic energy
  • move about more
  • increased chance of successful collisions
  • every 10 degree rise in temperature (up to the enzymes optimum) the enzyme activity doubles
  • Q10=
  • above  the optimum temperature the rate of reaction decreases
  • kinetic energy causes vibrations which start to break apart the secondary and tertriary structure of the protein structure by breaking the hydrogen bonding
  • the active site becomes denatured
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How pH affects rate of reaction

  • due to the number of amino acid R groups and carboxyl groups within an enzymes protein structure, they are extremely sensitive to pH
  • small changes in pH cause inactivation
  • big changes in pH cause denaturation
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How immobilised enzymes are used

  • immobilised enzymes are trapped or fixed in an inert matrix
  • such as alginate beads
  • beads may then be packed into glass columns
  • the substrate is added at the top
  • flows slowly over the alginate beads
  • product extracted at the bottom
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How a biosensor works

  • association of a biomolecule such as an enzyme
  • with a transducer
  • producesand electrical signal
  • in response to substrate transformation
  • strength of signal measured by a meter
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Use of biosensors to detect the presence of blood

  • electrode probe has glucose oxidase immobilised in the membrane
  • placed in a blood sample
  • if glucose is present, it diffuses thorugh the membrane
  • forms an enzyme substrate complex and oxygen uptake
  • (glucose oxidase catalyses a reaction between oxygen and glucose)
  • produces a small electrical current
  • picked up by the transducer
  • current is read by a meter
  • produces a reading for blood glucose
  • the rate of oxygen uptake is proportional to the glucose concentration
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