Bell Task

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Bell Task complete the following
Rate
Rate
Substrate Conc.
Temperature
Rate
Rate
pH
Enzyme conc.
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Inhibitors

• It is possible for some other molecule to bind to
  an active site or other part of enzyme
• This could inhibit enzyme function.

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Competitive Inhibitors

• Inhibitor binds briefly to the active site
• The inhibitor is similar to the substrate
• The inhibitor and the substrate compete for the
  active site

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What affects competitive inhibition?

• If there is more substrate than inhibitor, the
  substrate easily binds to active site and the
  enzyme function unaffected
• If there is more inhibitor than substrate, it is
  less likely for the substrate to meet active
  site and the enzyme function is inhibited

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Competitive Reversible

• Can be reversed by adding more substrate

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Competitive inhibition example

• Ethylene glycol is a toxic substance that is
  converted in the body to oxalic acid.
• Oxalic acid can cause permanent damage to the
  kidney.
• The active site of the enzyme that converts
  ethylene glycol to oxalic acid also accepts
  ethanol.

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Competitive inhibition

• Ethanol is an antidote to cure ethylene glycol
  poisoning. It is a competitive inhibitor.
• If the poisoned person is given a large dose of
  ethanol, the ethanol acts a competitive
  inhibitor, slowing down the reaction of the
  enzyme of ethylene glycol for long enough to
  allow the ethylene glycol to be excreted.

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Competitive inhibition example

• Methanol poisoning occurs because methanol is
  oxidized to formaldehyde and formic acid which
  attack the optic nerve causing blindness.

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Ethanol is an antidote

• Ethanol is given as an antidote for methanol
  poisoning because ethanol competitively inhibits
  the oxidation of methanol.
• Ethanol is oxidized in preference to methanol and
  consequently, the oxidation of methanol is slowed
  down so that the toxic by-products do not have a
  chance to accumulate.

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Non- Competitive

• 2 possibilities
• Inhibitor binds to different parts of the enzyme
  not the active site
• Inhibitor binds permanently to active site

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Binding to other sites

• Disrupts arrangement of H bonds and hydrophobic
  interactions
• Distorts 3-D shape of active site
• No longer fits substrate

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Irreversible or Reversible

• This depends on how long the inhibitor binds for.
• Irreversible if inhibitor is bound permanently
• Reversible if inhibitor is bound temporarily

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Example non competitive

• Antibiotic penicillin is a non-competitive
  inhibitor
• Binds permanently to the active site of an
  enzyme, produced by bacteria.
• Penicillin prevents the substrate from binding
  to the active site.
• This enzyme is essential for the production of
  bacterial cell walls. This stops bacteria from
  reproducing as new bacterial walls are not formed.

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Bacterial cell
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Inhibition lethal or useful

• Inhibition can be lethal e.g. antifreeze example
• In many situations inhibition is essential
• Enzymes in most reactions need to be controlled
  so they dont constantly churn out product.

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End-product inhibition

• One way to prevent excess product forming is to
  use the end product of a reaction as an
  inhibitor.
• As enzyme is converted to product, the reaction
  is slowed down as the product binds to the enzyme
  and prevents the substrate binding.

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End-product inhibition

• It is non-competitive because the end product ,
  does not bind to the active site but to another
  part of the enzyme.
• It is reversible because as the amount of the
  end product fall it does no longer bind to the
  enzyme and the enzyme regain activity

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Medicines is this true?

• Those that kill germs are irreversible.
• Antidotes are competitive or non-competitive but
  reversible.
• Those that treat a condition (heart problems,
  poisoning are reversible)