Measuring the Rate of an Enzyme Reaction
Calculates rate as amount per unit time, and in a defined colour-change method as 1000 divided by seconds. Describes how temperature and pH change enzyme rate, including the rise to an optimum and the possible irreversible fall after denaturation.
What a learner can do afterwards
- Calculates a rate from a time with consistent units.
- Sketches rate against temperature, marks the optimum, and marks where denaturing starts.
- Explains the fall after the optimum through the active site changing shape, not through the enzyme being used up.
1 · Read
A rate tells how much changes per unit time. Divide amount by time and state the units. In a colour-change experiment whose score is defined as 1000 divided by seconds, use that rule and label the result. On an amount-against-time graph, the slope shows amount per time, so a steeper initial slope means a faster initial rate. In a fair test, change one factor, repeat the measurement, and compare the results.
Temperature and pH can change enzyme rate, as can substrate amount and enzyme amount. A little warming often raises rate because particles move faster. They then collide more often and with more energy, and more collisions lead to a reaction. Too much heat can change the active site's shape. Keep the other conditions the same when testing one factor.
For a heat-sensitive enzyme, a rate-against-temperature graph rises to a peak and then falls. The peak is the optimum. Beyond it, denaturation can change the active site, so cooling may not restore the old rate. Different enzymes have different pH optima: pepsin works best in acidic conditions, while mouth amylase works best near neutral pH.
Read the rate and its units. Mark the peak as the optimum. If the active site has denatured, do not assume cooling rebuilds it.
Rate is change per time. A fair test changes one factor. Temperature and pH can produce an optimum, and denaturation may make the fall permanent.
Original enzyme-rate lesson and assessment text authored for the Hoofer taxonomy.
The rewritten readings were written for this dataset. The video is linked from Khan Academy. License terms for the video source are not recorded.
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