Core concepts Flashcards
Describe the lock and key model that explains how enzymes work
The shape of the active site of the enzyme is complementary to the shape of the substrate. This means that each enzyme will usually only catalyse one type of reaction - they are highly specific.
Explain what is meant by optimum conditions
Optimum conditions for an enzyme are where the maximum amount of enzyme-substrate complexes are being produced and the rate of reaction is at its fastest. The optimum temperature for an enzyme catalysed reaction is around 40⁰C. The optimum pH varies depending on the type of enzyme.
Explain the relationship between pH enzyme activity
Enzymes have an optimum pH at which the rate of reaction will be fastest. This optimum pH will vary depending on the enzyme, for example an enzyme in the stomach will have a more acidic optimum compared to one in the mouth. The shape of graph will always look like that below and at pHs above and below the optimum the rate of reaction will slow and eventually drop to zero as the active site gets denatured.
Calculate the rate of a reaction carried out by enzymes (H)
Look at how much of the substrate has been digested/how much product has been produced and divide by the time taken to do this.
Explain how to control an experiment investigating the effect of pH on enzyme activity (F)
If you were investigating the effect of pH on enzyme activity you would need to vary the pH as that is your independent variable.
All other factors that could affect the rate of enzyme activity need to be controlled e.g temperature (use a water bath), concentration of the enzyme and substrate solutions, volume of the enzyme and substrate solutions, surface area if dealing with solids, amount of mixing of the enzyme/substrate mixture.
Explain why denatured enzymes cannot catalyse reactions
Denatured enzymes cannot catalyse reactions because the active site has changed shape and will no longer fit with the substrate.
Explain the shape of a enzyme pH graph for the stomach enzyme pepsin and amylase found in the saliva
Pepsin is found in the stomach which contains hydrochloric acid so the optimum pH is quite low at around 2. If the pH increases or decreases we can see that the rate of reaction gets slower. This is because the active site of the enzyme becomes denatured. Amylase is found in the mouth where the pH is closer to neutral and we can see from the graph that the optimum pH for amylase is just below 7. As the pH increase and decreases from this optimum the rate of reaction decreases/gets slower. This is because the active site of the enzyme becomes denatured.
Describe how you would practically determine the optimum pH for an enzyme (F)
Mix together an enzyme and substrate (eg starch and amylase) and time how long it takes the reaction to complete. Repeat this experiment using buffer solutions of different pHs (at least 5 different pHs) and time how long the reaction takes. The pH at which the reaction is quickest is the optimum pH. You need to make sure you keep the temperature, concentration and volume of solutions the same for all experiments and that you do a set amount of mixing of the enzyme and substrate.
If you were using starch and amylase you would take samples of the mixture every 20/30 seconds and test for the presence of starch using iodine (it will turn blue black). When there is no more starch present then the reaction is finished.
