WEBVTT 00:00:03.840 --> 00:00:10.460 Which of the following statements correctly links enzymes, substrates, and active sites? 00:00:10.920 --> 00:00:17.710 (A) The substrate has an active site that has a complementary shape to a range of enzymes. 00:00:18.530 --> 00:00:25.160 (B) The enzyme has an active site that has a complementary shape to a specific substrate. 00:00:25.610 --> 00:00:31.820 (C) The enzyme has an active site that has an identical shape to a range of substrates. 00:00:32.200 --> 00:00:38.300 (D) The substrate has an active site that has an identical shape to a specific enzyme. 00:00:38.930 --> 00:00:45.990 (E) The enzyme’s active site is constantly changing to have a complementary shape to a range of substrates. 00:00:46.480 --> 00:00:53.280 The question asks us to find a statement that correctly links enzymes, substrates, and active sites. 00:00:53.640 --> 00:00:58.960 In order to answer this question, let’s go over the definition of each of these terms. 00:00:59.430 --> 00:01:10.870 An enzyme is often referred to as a biological catalyst because it speeds up the rate of reactions by lowering the activation energy required for the reaction to take place. 00:01:11.290 --> 00:01:14.450 These molecules are never used up in the reaction. 00:01:15.100 --> 00:01:16.900 Instead, they are recycled. 00:01:17.720 --> 00:01:24.860 Every enzyme has an active site, which is a region on the surface of the enzyme where its specific substrate will bind to. 00:01:24.860 --> 00:01:33.570 A substrate is a single molecule, or a combination of molecules, that has a complementary shape to the enzyme’s active site. 00:01:34.140 --> 00:01:40.710 This allows the enzyme and substrate to bind together and form the enzyme–substrate complex. 00:01:41.550 --> 00:01:52.600 Once the enzyme and substrate bind via the enzyme’s active site, thereby forming an enzyme–substrate complex, the substrate is converted into its products. 00:01:53.240 --> 00:02:00.400 Now that we have defined enzymes, substrates, and active sites, we can take another look at our answer choices. 00:02:01.130 --> 00:02:10.350 We need to find an answer that attributes the active site to the enzyme, since it is the enzyme that contains the active site and not the substrate. 00:02:10.950 --> 00:02:19.690 We also need to find an answer that highlights the complementarity between the enzyme’s active site and its specific substrate. 00:02:20.200 --> 00:02:24.810 Therefore, the correct answer to our question is answer choice (B). 00:02:25.660 --> 00:02:32.230 The enzyme has an active site that has a complementary shape to a specific substrate.