GCSE›Edexcel GCSE Biology›Mind mapsEnzymesEdexcel GCSE Biology: Mind mapStudy pack PDFAlso for this subtopic:Revision notesFlashcardsSubtopic testCover factsHow they workProtein catalysts that lower activation energyNot used up: they can be reusedActive site is complementary to one substrateLock and key gives specificityDenaturationHigh temperature breaks bonds holding the shapeExtreme pH does the sameActive site changes shape, substrate no longer fitsDenaturing is permanentRate factorsTemperature: rate rises to the optimum, then falls sharplySubstrate: rate rises then plateaus when sites are fullpH: fastest at optimum pHEnzymesbiological catalystsCalculationsrate=product formedtime\text{rate} = \frac{\text{product formed}}{\text{time}}rate=timeproduct formedTime to finish: rate=1time\text{rate} = \frac{1}{\text{time}}rate=time140 s → 140=0.025 s−1\frac{1}{40} = 0.025\,\text{s}^{-1}401=0.025s−1Energy in food: E=m×ΔT×4.2E = m \times \Delta T \times 4.2E=m×ΔT×4.2Food testsIodine: browny-orange → blue-black for starchBenedict's, heated: blue → brick-red for sugarsBiuret: blue → purple/lilac for proteinSudan III or ethanol: red stain / milky emulsion for lipidsExam tipsSay active site changes shape, not 'destroyed'Enzymes are not alive: never say they dieState the control variables for a fair testHeat loss makes calorimetry underestimate energy