The lock-and-key hypothesis and the induced-fit hypothesis are used to explain how enzymes interact with substrates. Describe one similarity and one difference between the lock-and-key hypothesis and the induced-fit hypothesis.
Iodine solution was used to check that starch was absent from extract E. State the colour seen when iodine solution is added to a sample of extract E.
The student placed a small drop of dilute starch solution and a solution of glucose 1-phosphate into a test-tube containing extract E. Every minute, samples of the reaction mixture were taken from the test-tube and iodine solution was added to each one. A colorimeter was then used to measure the absorbance of the solution in each sample. The results are shown in Fig. 3.2. Explain the results shown in Fig. 3.2.
After 12 minutes, the student added a solution containing phosphate ions to the reaction mixture. The student then kept taking samples every minute and added iodine solution to each sample. The absorbance of the solution in each sample was measured. The results showed that absorbance fell over time. Suggest why the absorbance decreased.
Muscle cells contain glycogen phosphorylase. Fig. 3.3 shows how caffeine affects the activity of glycogen phosphorylase at different substrate concentrations. A student concluded that caffeine acts as a non-competitive inhibitor of glycogen phosphorylase. Explain how the results in Fig. 3.3 support this conclusion.