Enzymes

• What are the key features of an enzyme

  • catalyse metabolic reactions
  • can affect structures / functions in a organism
  • can be intracellular or extracellular
  • globular proteins
• What is an active site

  Where the substrate binds to the enzyme

  They have a specific shape (determined by the tertiary structure)
• How do enzymes reduce activation energy

  holds two substrates (that are going to be joined) close together -> reduces any repulsion between molecules allowing them to form bonds easily

  Strains the bonds in a substrate that needs breaking down -> molecule then breaks down easier
• What are the main features of intracellular enzymes

  also known as endoenzymes

  work inside cells

  main reason for most biological processes eg catalase works to catalyse the breakdown of hydrogen peroxide (H2O2) into oxygen and water
• What are the key features of extracellular enzymes

  work outside cells

  Examples :

  Amylase:

  found in saliva (secreted by salivary glands)

  catalyses the hydrolysis of starch into maltose

  Trypsin:

  produced in pancreas and secreted into small intestines

  catalyses the hydrolysis of peptide bonds (making larger polypeptides into smaller ones (other enzymes break them down into amino acids))
• What is the lock and key theory

  The theory that substrate and enzymes are shaped perfectly complementary to each other
• What is the induced fit theory

  The theory that enzymes not perfectly complementary to their substrate and so will change shape in order to allow the substrate to fit
• How does enzyme concentration affect the rate of reaction (ROR)

  Increasing conc. increases ROR. This increases quickly to being with but gradually slows and plateaus as all the active sites are taken up by substrates
• How does temperature affect enzyme activity

  Below optimum:

  Increasing the temperature increases rate of reaction -> more kinetic energy in molecules -> more frequent collisions

  Above optimum:

  Increasing the temperature affects tertiary structure -> disulphide and hydrogen bonds begin to break -> active site changes shape -> enzyme denatures
• How can the pH affect enzyme activity

  If it is too high / too low -> ionisation of groups (in active site / substrate) may change -> slows / can prevent formation of enzyme-substrate complex

  EXTREME pH -> bonds maintaining tertiary structure are disrupted -> enzyme denatures
• How can substrate concentration affect rate of reaction (ROR)

  At low conc. -> reaction is slow -> not all active sites occupied -> increasing conc. increases ROR -> more active sites occupied -> eventually increasing conc. will not have an effect -> all active sites occupied -> turnover rate of enzymes determine ROR
• Why is the induced fit theory regarded as better than the lock and key theory

  The conformational change of the active site creates a better fitting active site for the substrate. This maximises enzyme activity
• Why are enzyme inhibitors used by the body

  To regulate the rate of reaction and how much product is formed
• What is inhibition

  Inhibition occurs when enzyme action is slowed or stopped by another substance.
• What are the two types of enzyme inhibitors

  • competitive
  • non-competitive
• How do non-competitive inhibitors work

  They bind to an enzymes allosteric site (NOT the active site). This changes the shape of the active site, stopping the substrate from binding to it

  They are a different shape to the substrate -> don't 'compete' for active site -> increasing the substrate concentration will have no effect on inhibition rate
• How do competitive inhibitors work

  They have a similar shape to the substrate. They will 'compete' for the active site, binding to it (but not reacting), blocking the active site. This stops the substrate from binding to the active site
• How do the concentrations of competitive inhibitors and substrate molecules affect inhibition rate


  • High inhibitor conc. -> more inhibitors taking up active site -> slows rate of reaction
  • High substrate conc. -> higher chance of enzyme-substrate complex forming -> speeds up reaction rate
• What is end-product inhibition

  • a form of negative feedback that controls metabolic pathways
  • functions to regulate amount of essential product
  • final product in a reaction series inhibits an enzyme in the earlier stages -> inhibits non-competitively -> enzyme can no longer function -> reaction sequence stops -> product creation rate slows
• What are cofactors

  • most are organic molecules of ions -> can be gotten by diet
  • work by helping enzymes and substrates bind together
  • don't directly participate -> don't get changed or used up
  • becomes known as a prosthetic group if it is tightly bound to enzyme
• What are coenzymes

  • organic molecules -> derived from vitamins
  • participate in reaction and get changed by it
  • often act as carriers, moving chemical groups between different enzymes -> continually recycled during this process
• What is precursor activation

  • some enzymes cause damage inside cells -> present in inactive form until needed
  • precursor enzymes need to change tertiary structure (active site specifically) -> done by adding cofactor
  • BEFORE cofactor added -> known as apoenzyme
  • AFTER cofactor added -> known as haloenzyme