enzyme action

• anabolic reactions- building up
• catabolic reactions- breaking down
• lock and key hypothesis

  • only a specific substrate will fit the active site of an enzyme
• enzyme + substrate = enzyme substrate complex = enzyme +products
• induced fit hypothesis

  • the active site changes shape slightly as the substrate enters
  • initial interaction is relatively weak, these interactions cause changes in the enzymes tertiary structure
  • this can weaken bonds in the substrate molecule, lowering the activation energy
• intracellular enzymes

  • act within cells
• extracellular enzymes

  • released by cells to break down nutrients
• starch

  • amylose breaks starch polymers into maltose
  • maltase breaks maltose into glucose
• proteins

  • trypsin breaks proteins down into peptides
  • protease breaks down peptides into amino acids
• temperature coefficient

  • how much rate of reaction increases with 10 degree rise in temp
• temperature

  • when enzyme is denatured, its no longer complimentary to the substrate (no longer functions)
• psychrophiles

  • optimum temperature is below 5 degrees
  • less stable
• thermophiles

  • optimum temperature is 70 degrees
  • can withstand longer temperature ranges
• renaturation- pH returns to optimum and enzyme returns to its normal shape and catalyses the reaction again
• pH

  • hydrogen and ionic bonds between amino acid R- groups hold proteins in their precise 3D shape
  • change in pH = change in hydrogen ion concentration
  • active site will only be the right shape at a certain hydrogen concentration
• enzyme inhibitors

  • molecules that slow down/ stop enzymes from catalising reactions
• competitive inhibition

  1. a molecule with similar shape to the substrate fits into the enzyme active site
  2. prevents substrate from entering the active site, prevents enzyme catalising reaction

  • reversible
  • eg statins
• non competitive inhibition

  1. inhibitor binds to allosteric site (alternative to active site)
  2. this changes the tertiary structure of the enzyme and its active site
  3. active site can no longer accept the substrate

  • irreversible
  • eg proton pump
• end of product inhibition

  • the product of a reaction acts as an inhibitor for the enzyme (negative feedback prevents waste)
  • eg PFK inhibited by ATP
• cofactors

  • helper molecule (inorganic)
  • forms part of active site
  • not used up in reaction
  • obtained via diet
  • amylase
• coenzymes

  • responsible for transfer of hydrogen in respiration
  • organic molecule
  • continually recycled
  • eg coenzyme A
• prosthetic groups

  • permanent feature on enzyme
  • inorganic molecules
  • haem group of haemoglobin