#2.4 Enzymes

• enzymes are biological catalysts made of globular proteins
• • the active site is specific and unique in shape due to specific folding and bonding in the tertiary structure of the protein

  -> due to this specific shape, enzymes can only attach to substrates that are complementary in shape
• enzymes catalyse intracellular and extracellular reactions , e.g.

  • catalase

  intracellular in liver cells that breaks down hydrogen peroxide into oxygen and water

  • trypsin

  extracellular inside small intestine that digests protein by hydrolysing peptide bonds
• Activation energy

  • minimum amount of energy needed by reactants for a chemical reaction to occur

  → when enzymes attach to the substrate they can lower the activation energy needed for reaction to occur and therefore speed up reaction
• Lock + Key Hypothesis

  • enzyme is the lock
  • substrate is the key
  • the enzyme active site is a fixed shape and due to random collision the substrate can collide and attach to the enzyme forming an enzyme-substrate complex and charged groups within the active site are thought to distort the substrate and therefore lower activation energy
• Induced Fit Hypothesis

  • hypothesis suggests that enzyme is like a glove and substrate is like your hand
  • enzyme active site is induced

  induced fit is when enzyme active site is induced, or slightly charger shape, to mould around substrate

  →when es complex occurs it puts strain on the bonds and therefore lowers activation energy
• enzymes are globular proteins sensitive to certain conditions

  Factors affecting enzymes :

  • temperature
  • pH
  • enzyme concentration
  • substrate concentration
  • inhibitors concentration
• Factor : Temperature

  if the temperature is too low there is insufficient kinetic energy for successful collision

  • if temperature is too high enzyme denature, the active site changes shape and enzyme-complexes form
  • →high temperature causes bonds to break and tertiary structure alters, causing a change in shape of active site
• Factor : pH

  too high or too low a pH will interfere with the charges in the amino acids in active site

  alters tertiary structure and changes shape of the active site and enzyme denatures

  enzymes have different optimal pH values that they work at
• Factor : Substrate and enzyme concentrations

  If there is low concentration of substrate, the reaction will be lower as there will be fewer collisions between the enzyme and substrate

  Increasing the substrate concentration will increase the rate of reaction

  at high substrate concentrations rate of reaction will plateau because all enzyme active sites are in use (enzymes are saturated)
• Factor : Substrate and enzyme concentrations 2

  • low enzyme concentration there will be a lower rate of reaction
  • increasing enzyme concentration as es complexes will be more likely to form
  • →at high enzyme concentrations,the rate of reaction plateaus as there is insufficient substrate to bind with Large number of enzymes
• Substrate and enzyme concentrations are inversely proportional to each other.

  
• the Q10 temperature coefficient

  measure of the rate of change of an enzyme-controlled reaction as a result of increasing the temperature by 10°C

  Formula: Q10= R2/R1

  R1 = rate of reaction at a temperature of X°C

  R2 = rate of reaction a temperature (x+10)°C
• Competitive Inhibitors

  COMPETITIVE

  →same shape as substrate and complementary in shape to the active site; therefore, they bind to the active site

  • they prevent the substrate from binding and enzyme-inhibitor complexes form instead of enzyme-substrate complexes and rate of reaction is lower
  • most competitors are reversible

  →reversible is if it can be removed whereas non-reversible can't be removed from enzyme
• Non-competitive Inhibitors

  NON COMPETITIVE

  →bind to enzyme away from active site called allosteric site,causing protein to change shape ; therefore substrate can no longer bind regardless of how much substrate is added

  • fewer es complexes form and rate of reaction is lower
• Competitive Inhibitors 2

  if a high enough concentration of substrate is added, the substrate can knock out the inhibitor and therefore rate of reaction will increase

  →colliding into inhibitor

  
• End Product Inhibition

  • the products of some reactions are reversible inhibitors for enzymes involved in controlling reaction

  →enabling reactions to be controlled

  • if there is a lot of product present, it will inhibit enzymes and cause reaction to slow or stop ; preventing resources from being wasted
• Coenzymes,Cofactors and Prosthetic Groups

  some enzyme controlled reactions require an additional non-protein molecule such [the title of this part] to catalyse a reaction
• coenzymes + cofactors

  • some reactions require atoms to be carried from one reaction to the next in multi-step pathway reactions
  • some enzymes also require a non-protein molecule to bind the active site to make it complementary to substrate

  the difference is coenzymes are organic molecules and cofactors are inorganic molecules
• prosthetic groups

  type of cofactor but they differ in that they are permanently attached to enzyme by covalent or non-covalent forces
• • venom is introduced into the victim's body by injection - e.g. Snake bite
  • poisons are toxins that are ingested