enzymes

• enzymes

  biological catalysts so they increase rate of reaction by decreasing the activation energy
• induced fit model

  when an enzyme-substrate complex is formed, the structure of the enzyme alters so that the active site of enzyme fits around the substrate
• extracellular enzymes

  enzymes that catalyse digestion of macromolecules into smaller organic molecules which are then absorbed
• effect of temperature

  as temp increases, rate of reaction increases due to increase of kinetic energy in the particles which results in more frequent successful collisions so more enzyme-substrate complexes are formed

  when optimum temp is exceeded the rate of reaction decreases due to the vibrations from more kinetic energy break the Hydrogen bonds resulting in enzyme denaturing
• denaturing

  when the active site’s structure is damaged, due to tertiary structure being damaged, so the substrate is no longer able to bind with the enzyme
• temperature coefficien Q10=rate of reaction at (T+10)/rate of reaction at T
• effect of ph

  as the pH increases so does rate of reaction but once it’s past the optimum ph the rate of reaction decreases because it causes a change in concentration of hydrogen ions therefore disrupting the tertiary structure of the protein so the enzyme becomes denatured and the structure of the active site is lost so substrate-complexes can no longer form
• effect of substrate concentration

  as substrate concentration increases, rate of reaction increases because there would be more frequent successful collisions, therefore more enzyme-substrate complexes

  it stops increasing after the saturation point (all active sites are saturated) is reached
• when substrate concentration is no longer limiting rate of reaction can reach Vmax - can be reached by controlling enzyme concentration, temperature and pH; it’s reached when substrate concentration is no longer limiting as the substrate concentration has reached a point where all active sites are occupied
• effect of enzyme concentration

  as enzyme concentration increases, rate of reaction increases because there would be more frequent successful collisions so amount of enzyme-substrate complexes are formed increases

  since amount of enzymes is much higher than substrates, substrate concentration is the limiting factor therefore increasing the enzyme concentration past a certain point has no effect on rate of reaction
• competitive inhibitors are similar in structure to the substrate therefore able to bind with active site and competes with the substrate
• competitive inhibition

  • the inhibitor enters the enzyme’s environment
  • the molecules are moving and an inhibitor may arrive at the active site and bind to it, preventing the substrate from binding
  • as amount of inhibitors increases the rate of reaction decreases
  • this can be reversed by increasing the substrate concentration
  • Vmax is unaffected
• non competitive inhibitors bind to the enzyme at a site other than the active site called the allosteric site which changes the active site’s shaped so the substrate can no longer bind to it
• non competitive inhibition

  • inhibitor enters enzyme’s environment
  • inhibitor binds to allosteric site
  • once its binded a reaction occurs, changing the tertiary structure of the active site so the substrate can no longer bind
  • can’t be reversed by increasing substrate concentration and Vmax is affected
• reversible inhibitors

  • they bind to the active site through hydrogen bonds and weak ionic interactions therefore don’t bind permanently
  • can be competitive or non-competitive
• irreversible inhibitors

  • cause disulphide bonds within protein structure to break causing the active site to change
• cofactors are non-protein molecules, atoms or ions that are required for enzyme activity to occur by binding loosely to an atom
• coenzymes are organic cofactors which don’t bind permanently which are usually derived from vitamin, they facilitate the binding of a substrate to enzyme and can be removed but are needed for activity

  an example is NADP which is used for photosynthesis
• prosthetic groups are permanently attached to the enzyme and are not involved in the active site, they’re made of non-protein, organic or inorganic ions

  for exmample Zn+ for carbonic anyhydrase
• activators are inorganic metal ions which temporarily alters the active site making the reaction more feasible

  for example Mg2+ is involved on shielding negative charge