Chp 5

• the main features of enzymes are their specifity for a substrate and their catalytic power
• enzyme specifity is the ability of an enzyme to only catalyse a specific reaction by binding to the substrate
• enzymes do not make reactions occur that wouldnot occur on their own only making them occur faster
• to catalyse = to increase the rate of the reaction
• active site = key feature of an enzyme
• when the active site binds to the substrate it is a enzyme-substrate complex
• two models of how enzymes and their subsrtates interact

  • the lock and key model - the active site is the lock and thesubstrate is the key
  • the induced fit model
• the induced fit model is when a substrate binds to the active site of an enzyme a change in shape of the active site occurs
• enzyme reactions are often reversible
• different enzymes can catalyse a reaction in ech direction
• all reactions need activation energy to start the reaction
• the catalytic power of enzymes comes form being able to reduce the level of activation energy
• photosynthesis equation (word)


  carbon dioxide + water - light energy - glucose + oxygen + water
• photosynthesis equation (chemical)

  6CO2 +12H2O - light energy - C6H12O6 + 6O2 + 6H2O
• enzymes have optimum conditions in which they perform their best
• higher temperatures increase molecular collisions up to the point where the enzyme is denatured and function rapidly ceases
• pH - function is decreased either side of the optimum and the enzyme may be denatured outside a tolerance range
• substrate concentration - rate increases with more molecular collisions until all active sites are occupied, the saturation point is reached and the rate plateaus
• inhibition of an enzyme by an inhibiting molecule
• reversable inhibition - bonds between inhibitor and enzyme are weak, binding is only temporary
• irreversible inhibition - bonds between inhibitor and enzyme are strong, cannot be broken without also breaking apart the enzyme
• competitive inhibition - the shape of the inhibitor is similar to the shape of the substrate that normally binds to the active site , the inhibitor blocks the substrate and does not trigger a catalytic reaction
• non-competitive inhibitor - the inhibitor binds to an allosteric site (enzyme site other than the active site), binding to the allosteric site either changes the shape of the enzyme or prevents a catalytic reaction from proceeding even if the substrate is bound
• feedback inhibition - when a product produced late in a pathway is also an inhibitor of an enzyme earlier in the pathway
• regulation of enzymes refers to the mechanisms by which the activity of enzymes is controlled within cells
• above the optimal temperature, the kinetic energy becomes too high and the bonds that hold 3D shape of the enzymes begin to break
• increasing enzyme concentration increases the rate of reaction provided there is an excess of substrate
• increasing substrate concentration results in faster rate of reaction until all enzyme molecules are working at capacity
• enzymes reduce activation energy by influencing

  • proximity and orientation
  • the micro environment
  • ion exchange
• proximity and orientation - enzymes bring the parts of the molecule closer together in the active site
• the micro environment - most active sites are hydrophobic which results in a non-polar environment that allows stabilising interactions, hydrophobic imteractions and dispersion forces to occur
• ion exchange - amino acids in the active site can often take H+ ions from, or donate them to, the substrate to facillitate steps in reaction
• a biochemical pathway is a sequence of biochemical reactions catalysed by different enzymes, in which the product of each reaction becomes the substrate in the next reaction
• biochemical pathways may be linear, branched or cyclic (the initial molecule is regenerated)
• plants trap solar energy and convert it into chemical energy stored in the bonds of glucose molecules
• a light dependent stage that converts light energy into chemical energy (ATP)
• a light-independent stage that uses ATP to synthesise organic compunds
• energy released from glucose through cellular respiration is used to generate chemical energy (ATP)
• worded equation for cellular respiration

  glucose + oxygen -> carbon dioxide + water +energy (ATP)
• chemical equation for cellular respiration

  C6H12O6 + 6O2 -> 6CO2 + 6H2O +ATP