Enzymes

• Catalase is an important enzyme that breaks down the toxic hydrogen peroxide into water and oxygen in our cells.
• Enzymes are tertiary structure globular proteins that act as biological catalysts by lowering activation energy
• Each enzyme is specific to one type of substrate.
• An Anabolic reaction is one which builds up.
• A Catabolic reaction is one which breaks down.
• The Induced fit model states that the tertiary structure of enzymes change as a substrate approaches to ensure that the active site perfectly fits it. Once products are formed it returns to its original shape.
• The substrate reacts with the r groups of amino acids on it's specific enzyme to form bonds that help strain the substrate and lower activation energy.
• Any factor which increases the number of successful collisions between the active site and the substrate will increase the rate of reaction.
• Too high a temperature breaks the hydrogen bonding in the active site, denaturing the enzyme.
• On a graph showing the effect of substrate concentration on rate of reaction, the graph will eventually plateau as all enzymes would be saturated.
• Q10 = Rate of reaction at x=10 degrees / rate of reaction at x degrees.
• Large changes in pH will disrupt the hydrogen bonding of the active site causing it to deform and be unable to form enzyme substrate complexes.
• A higher concentration of reactants means more molecules per unit volume so there is an increased chance of them colliding. This leads to a greater frequency of successful collisions and therefore a faster rate of reaction.
• Competitive inhibitors compete with substrate molecules for the active site but no products are produced.
• By occupying the active site, competitive inhibitors prevent collisions between active site and substrate so the rate of reaction decreases when the enzyme is saturated.
• We can reduce the affect of temporary competitive inhibitors by increasing substrate concentration, increasing the likelihood of collisions between substrate and active site.
• The ' Vmax ' is the maximum rate of reaction of a reaction.
• The allosteric site is a region of an enzyme separate to the active site where non-competitive inhibitors, co-factors and co-enzymes can bind to.
• Non-competitive inhibitors bind to the allosteric site of an enzyme and cause a conformational change that changes the tertiary structure of an enzyme so the active site isn't complimentary to a substrate.
• Non-competitive inhibitors are irreversible and also decrease rate of reaction. They cannot be countered by increasing concentration of substrate.
• The product of one reaction is often the substrate for the next reaction in a metabolic pathway.
• The cell uses end product inhibition to regulate a metabolic pathway. This is a negative feedback loop.
• The end product of a pathway may be the inhibitor to an early stage enzyme and is able to reduce rate of reaction in the pathway to keep the amount of a product in a certain range.
• End product inhibitors are non-competitive inhibitors as they bind to the allosteric site of an enzyme
• Many enzymes function in partnership with other chemicals called co-factors.
• Amylase needs a chloride ion co-factor to catalyse the hydrolysis of starch.
• Cofactors can be complex organic molecules and at which point are referred to as co-enzymes.
• NAD is an example of a co-enzyme. it transfers hydrogen atoms from one molecule to another by binding to enzymes involved in respiration.
• Many co-enzymes come from vitamins in our diet e.g. Niacin ( vitamin B3 ) is a source of NAD.
• In some cases, cofactors are permanently binded to the structure of an enzyme and so are called prosthetic groups.
• Carbonic anhydrase is permanently bound to Zn2+ ion, and so in this case the zinc cation is referred to as a prosthetic group.