1.7 - Enzyme Action

• enzymes

  globular proteins that act as biological catalysts, speeding up the rate of chemical reactions without undergoing permanent change themselves so can be reused repeatedly
• enzyme activity

  can affect structures and functions in an organis

  can be intracellular or extracellular
• activation energy

  minimum amount of energy needed to activate the reaction
• conditions needed for reactions to happen naturally

  reactants must collide with enough energy to alter the arrangement of their atoms to form the products

  the free energy of the products must be less than that of the reactants
• how enzymes work

  they lower the activation energy so reactions happen at a lower temperature which speeds up the rate of reaction

  enables metabolic processes to happen rapidly at a human body temperature of 37°C so life can be sustained
• how enzymes lower activation energy

  substrate fits into the enzyme forming an enzyme substrate comples (ESC)

  if substrate molecules need to be joined enzyme holds reactants together so reduces repulsion between them so they bond more easily

  if substrate needs to be broken down, the ESC puts a strain on the bonds of the substrate so it breaks up more easily
• active site

  specific region of the enzyme that's functional and forms a small depression within the enzyme molecule

  made of a small number of amino acids
• substrate

  molecule on which the enzyme acts

  it fits into the active site forming an enzyme substrate complex and is held there by temporary bonds between amino acids of active site and groups on substrate molecule
• shape of enzyme

  specific 3D shape due to they primary structure

  so only catalyse one reaction as only one complementary substrate will fit into the active site
• tertiary structures of enzymes

  each enzyme has a different tertiary structure so has a different active site

  if tertiary structure is altered the shape of the active site changes so substrate won't fit so ESC won't form so enzyme won't be able to carry out its function
• what can alter the tertiary structure


  pH

  temperature

  genes: determine primary structure so if there's a mutation it could change the tertiary structure of the enzyme
• lock and key model

  substrate will only fit the active site of one particular enzyme as substrate has to fit perfectly into the active site like each key has a specific shape that fits and operates a single lock
• lock and key model is supported by

  observation that enzymes are specific in the reactions they catalyse
• limitation of the lock and key model

  enzymes can have molecules bind to them in areas other than the active site so enzyme in flexible and not rigid

  enzyme substrate complex changes shape slightly
• induced fit model

  active site forms as the enzyme and substrate interact

  substrate causes enzyme to change shape that forms the active site

  substrate must be the right shape to fit into the active site and make the active site change shape in the right way which will put a strain on the substrate distorting bonds which lowers the activation energy

  enzyme is flexible and can mould itself around the substrate like a glove moulds itself around a hand