Enzymes

• • enzymes are globular ( 3D ) proteins helping to speed up chemical reactions by lowering activation energy without being used up
  • for a reaction to happen bonds have to be broken
• 1.Lock and key theory

  • active site on enzyme and substrate have complementary fit forming enzyme-substrate complex
  • due to this enzymes are said to be specific
• 2.Induced fit model

  • active site has specific shape which only binds to complementary substrate
  • enzyme alters shape slightly to surround appropriate substrate as it binds
  • once enzyme surrounded substrate it puts strain specific bonds lowering activation energy
  • therefore enzyme and substrate not complementary at the start
• • shape and active site of enzyme determined by sequence of amino acids in primary protein structure
  • if amino acid is changed it can change 3D structure due to different folding
  • change in structure can result in different enzyme or loss of function of enzyme
• Factors that affect functioning of enzymes

  • ph
  • temperature
  • substrate concentration
  • enzyme concentration
  • inhibitors
• 1.Temperature

  • higher the temperature the more kinetic energy causing more collisions increasing ROR
  • enzyme gains so much energy breaking weaker hydrogen bonds in tertiary structure
  • tertiary structure and active site and function is lost causing enzyme to denature
  • temperature coefficient is Q10. Enzyme reactions considered to be 2 meaning ROR doubles every time temp increases by 10°
• 2.PH

  • each enzyme has different optimum ph ( quantity of H+ ions )
  • if ph surrounding enzyme is different to enzymes optimum it can cause it to stop working / denatured
  • ph affects enzyme activity due to preventing enzyme substrate complexes being formed and causes a loss of tertiary structure because the H+ ions interact and break weaker hydrogen bonds and ionic bonds
  • as tertiary structure lost so is active site meaning enzyme can’t function
• 3.Effect of substrate concentration on enzyme activity

  • enzyme concentration kept the same but substrate concentration gradually increased the ROR increases at first then remains the same because at the start of reaction there’s more enzyme than substrate meaning there are active sites with no substrate attached
  • as more substrates added more active sites become occupied causing ROR to increase , ROR fastest when all active sites are occupied
  • When more substrate than enzyme ROR is same because there’s not enough active sites so they have to wait until one comes available
• 4.Effect of enzyme concentration on enzyme activity

  • low enzyme concentrations there are more substrate molecules than available active sites, by increasing number of active sites it increases ROR
• • competitive inhibition - structurally similar to substrate that binds to active site
  • non competitive inhibition - binds to enzyme but not the active site instead the allosteric site that changes the active site
  • inhibitors reduce ROR by reducing enzyme activity
• competitive inhibitors

  • inhibitor isn’t permanently bound
  • binds to active site
  • similar shape to substrate molecule
  • effect of inhibitor depends on relative substrate
  • lots of substrate means harder for inhibitor molecule to bind meaning enzyme activity isn’t affected much
  • if concentration of substrate reduces or the concentration of the inhibitor molecule rises then its harder for correct substrate to bind so enzyme activity falls
  • it’s reversible
• Competitive inhibitor example

  • ethylene glycol and ethanol both bind to the same active site
  • when ethylene glycol binds its converted into oxalic acid which damages kidney
  • large dose of ethanol given to prevent kidney damage as it helps to slow down the oxalic acid providing time for the ethylene glycol to be removed from the body
• Non competitive inhibitors

  • reversible/irreversible non competitive inhibition: when an inhibitor molecule binds to another site on the enzyme that isnt the active site. Known as the allosteric site. when inhibitor binds it interacts with hydrogen bonds and hydrophobic interactions causing a change in the 3D structure. Change in structure makes active site no longer complementary to substrate. Enzyme unable to function while the inhibitor is bound.
  • If inhibitor binds permanently then its irreversible but if it binds briefly its reversible
• • many reactions in body involve several steps and can create waste products that can be toxic in high concentrations
  • to prevent toxic build up product behaves as non-competitive reversible inhibitor
  • inhibitor molecule (toxic product ) binds to allosteric site on the first enzyme and temporarily prevents enzyme function
  • means reaction is temporarily stopped allowing toxic product to be removed from the body and not create anymore
• Main types of cofactor to allow enzymes to function properly

  • co enzymes
  • inorganic ions
  • prosthetic groups
• Co-enzymes

  • organic molecules that contain vitamin molecules as part of structure
  • become loosely bound to enzyme and move away from enzyme once reaction complete
  • one co-enzyme e.g NAD+ may react with many different enzymes in many types of different reactions
  • NAD+ transfers hydrogen in reactions involving dehydrogenase enzymes
• Inorganic metal ions

  • known as enzyme activators
  • change charge of active site enabling enzyme substrate complex to form
  • some are intimately bound to enzyme but most just accelerate binding between enzyme and substrate
• Prosthetic groups

  • co-enzymes that bind permanently to enzyme molecule and remain there even after reactions complete e.g FAD ( flavin adenine dinucleotide )
  • like NAD+ it carries hydrogen atoms but this time with oxidase enzymes