OCR A level Enzymes

• Metabolism

  Enzyme controlled reactions
• Intracellular enzymes

  Work inside a cell e.g. catalase that breaks down hydrogen peroxide
• Extracellular enzymes


  Are secreted outside the cell where it functions e.g. amylase and trypsin break down large food molecules outside the cell so that the small products can be absorbed
• Tertiary structure


  The 3D shape of an enzyme that is necessary for it to function
• Specificity

  An enzyme only carries out one reaction because of the shape and charge distribution in the active site
• Active site

  A cleft on an enzyme where the substrate binds
• Lock and key hypothesis

  The shape of the substrate is complementary to the shape of the active site so they can bind together and form an enzyme substrate complex
• Induced fit hypothesis

  As the substrate binds into the active site the enzyme changes shape around the substrate forming a transition complex that puts strain on the bonds in the substrate molecule
• Enzyme product complex

  Once the reaction has occurred the enzyme product complex becomes an enzyme product complex and then the product is released
• Activation energy

  The energy needed to carry out the reaction, this is much lower when an enzyme is involved because it provides and alternate reaction pathway
• Transition state

  The substrate is converted into the product through an intermediate form in an alternate reaction pathway
• Low/high pH

  The quantity of H+ and OH- ions around the enzyme affects the 3D shape of the active site and affects how well a substrate can bind, if the change in pH is extreme then the enzyme will denature.
• Low temperature


  The frequency of collisions is lowered which results in fewer enzyme substrate complexes being formed, the enzyme is not denatured.
• High temperature


  Very frequent collisions between molecules cause vibrations within the enzyme that causes hydrogen bonds to be broken, this changes the shape of the active site and the enzyme is denatured.
• Enzyme concentration


  The rate of reaction increases because more active sites are available, so more enzyme substrate complexes can form until the concentration of substrate is limiting
• Substrate concentration

  The rate of reaction increases because the substrate can bind into empty active sites forming more enzyme substrate complexes until the enzymes become saturated
• Serial dilution

  A solution is diluted repeatedly making very low concentrations
• Coenzymes


  are non-protein biological molecules that bind with the substrate and are often changed during the reaction.
• Cofactors

  a substance that increases enzyme activity
• Inorganic ion cofactor


  This binds the enzyme during the reaction affecting the charge of the active site and increases the likelihood of substrate binding
• Prosthetic group


  A permanent but non-protein component of an enzyme that is necessary for it to function
• Coenzyme example

  NAD from vitamin B3
• Cofactor for amylase

  Cl-
• Prosthetic group for carbonic anhydrase

  Zn2+
• Enzyme inhibitor

  Reduces the rate of enzyme controlled reactions
• Competitive inhibitor

  Binds to the active site and reduces the rate of substrate binding (by blocking it), this is overcome at very high substrate concentrations and the maximum rate can still be achieved
• Non-competitive inhibitor


  Bind away from the active site (allosteric site) this affects the shape of the active site preventing the substrate from binding. The maximum rate of reaction is lowered.
• Reversible inhibitors


  An inhibitor that binds temporarily to the enzyme, often a competitive inhibitor
• Non-reversible inhibitors


  An inhibitor that binds permanently to the enzyme preventing the enzyme from working.
• Metabolic poison

  An enzyme inhibitor that prevents an essential enzyme reaction from occurring this may result in the accumulation of a toxic product
• Inhibitors as medicines

  An enzyme inhibitor can be used to stop or reduce enzyme reactions that are having adverse effects on a patient
• Product inhibition

  The product of a reaction binds to an enzyme in an enzyme pathway, preventing an earlier reaction so that this product does not accumulate.
• Inactive precursor


  A protein that will be converted into an active form only when required such as prothrombin into thrombin in the blood clotting cascade.