Final answer:
In enzyme labs, substrate is added to test tubes at the last moment to start the reaction simultaneously across all samples and prevent premature enzymatic activity, which could skew the initial rate measurements crucial for enzyme kinetics studies.
Step-by-step explanation:
When preparing test tubes in enzyme labs, one waits until the last moment to add substrate to ensure that the reaction starts at a precise and controlled time across all test tubes. This ensures consistency when measuring the initial rate of product formation, which is critical for determining the kinetics of an enzymatic reaction. If the substrate were added too early, the reaction could begin at different times in different tubes, making it difficult to accurately compare the initial rates of reaction. Additionally, because enzymes can become saturated with substrate, adding substrate last prevents the reaction from proceeding before the actual experiment begins, which might affect the accuracy of results.
Designing a steady-state experiment requires careful planning of the amount of the enzyme, substrate, and buffer volumes. The substrate concentration must be carefully controlled to gain insights into enzyme kinetics, particularly because increasing the concentration of substrate will not always increase the rate of reaction due to enzymatic saturation. For accurately interpreting results, it is essential to ensure that the condition at which each reaction is initiated is the same as the other test tubes in the assay.