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Enzymes – the story so far. Enzymes are biological catalysts Speed up reactions Lower the energy needed to make reactions proceed Enzymes react with substrates - very specific Substrates have a structure complimentary to the active site of the enzyme (‘lock & key’)

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enzymes the story so far
Enzymes – the story so far
  • Enzymes are biological catalysts
  • Speed up reactions
  • Lower the energy needed to make reactions proceed
  • Enzymes react with substrates - very specific
  • Substrates have a structure complimentary to the active site of the enzyme (‘lock & key’)
  • Reaction complete = enzyme is unchanged
  • Can help ‘build-up’ or ‘breakdown’ reactions
enzymes ctd
Enzymes ctd.
  • Can be intracellular or extracellular
  • All made of protein, most globular
  • Amino acid sequence, and bonding between them, determines active site shape

All have an active site

factors affecting enzymes
Factors affecting enzymes
  • Temperature:
  • Increasing temp makes atoms vibrate
  • above 40oC, vibrations break chemical bonds holding enzyme together
  • Structure unravels, active site is lost
  • = denatured
  • pH:
  • All enzymes have an optimum pH
  • Mostly close to neutral (5-9)
  • exceptions
  • - pepsin (2-3)
  • - alkaline phosphatase/phosphorylase (10)
factors affecting enzymes1
Factors affecting enzymes
  • Enzyme concentration:
  • - enzyme-substrate reaction is very brief
  • - enzyme then moves on to the next substrate molecule
  • Turnover Number:
  • - no. of substrate molecules which an enzyme acts on in a given time
  • range: 100-4000 per second
  • Increased enzyme conc. = increased reaction rate
  • This will increase at a steady rate as long as there is substrate present
factors affecting enzymes2
Factors Affecting Enzymes
  • Substrate Concentration:
  • Increasing substrate conc. will increase reaction rate
  • - more substrates binding with active sites
  • After a certain point all the active sites will be filled
  • Therefore increasing substrate conc. will no longer have an effect
inhibitors
Inhibitors
  • Competitive:
  • - compete directly for enzyme’s active site
  • - have a structure very similar to that of the substrate
  • - active site gets blocked
  • - reaction rate goes down as more sites get blocked by inhibitor
  • - increasing substrate conc. can return reaction rate to normal
inhibitors1
Inhibitors
  • Non-Competitive:
  • - Don’t combine with active site
  • - Attach to another region on the enzyme
  • - This results in the active site structure being altered indirectly
  • e.g cyanide, heavy metals
  • - increasing substrate conc. will not return reaction rate to normal
activation of enzymes
Activation of Enzymes
  • Co-Factor:
  • A non-protein substance which helps to activate an enzyme
  • e.g. Zn, Fe, Cu, Mg
  • Often helps the substrate to fit the active site
  • Some are known as Co-Enzymes
  • These are mostly made of vitamins
  • e.g. Vitamin B - transfers Hydrogen during aerobic respiration
other enzymes
Other Enzymes
  • Many digestive enzymes start off inactive
  • In the gut they’re activated by enzyme activators
  • e.g. trypsin & chymotrypsin in the pancreas
  • - both protein digesting enzymes
  • - if permanently active, could digest the pancreas itself
  • InactiveActivatorActive enzyme
  • trypsinogen+ enterokinase trypsin
  • Chymotrypsinogen + trypsin chymotrypsin + trypsin
inborn errors of metabolism
Inborn Errors of Metabolism

(PKU)

  • Metabolism - sum of all the chemical reactions in the body
  • Products of one reaction often go into another reaction
  • All reactions controlled by enzymes
  • If a genetic fault occurs, the enzymes are not produced correctly
  • Intermediate metabolites accumulate and cause disorders
  • e.g. albinism, PKU
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