Enzymes and Energy
In general, enzymes are protein molecules which must be folded in a specific three-dimensional shape in order to function properly. Certain environmental parameters can affect enzyme activity, including pH and temperature. If an enzyme’s shape changes significantly and it can no longer function, the enzyme is said to have become denatured.
The enzyme pancreatic amylase is manufactured and secreted by the pancreas into the duodenum (the large, beginning portion of the small intestine). Pancreatic amylase breaks down starch into maltose, a disaccharide. Pepsin is an enzyme that is released by the epithelium of the stomach, and functions in the stomach to break down proteins into smaller polypeptide units.
The following graphs show the activities of various enzymes under various environmental conditions.
Which of the following statements is true with respect to graph 1?
|A||Pepsin and pancreatic amylase could never function together in the same part of the body at the same time.|
|B||Pancreatic amylase could function in the stomach, but its activity would be low.|
|C||The optimal pH for the functioning of pepsin is approximately 8.5.|
|D||Normally, the small intestine must be slightly acidic.|
We can tell that this is true because the ranges of activity depicted by the graph do not overlap. Therefore, no pH value exists at which both enzymes will be even slightly active. It is assumed that the general pH values are known for the stomach and small intestine, approximately 2 and 8 respectively. Therefore, the graph confirms that pancreatic amylase will have no activity at pH 2 (choice B), but that this is the optimum for pepsin (not 8.5, as is suggested in choice C.) The graph additionally shows that pancreatic amylase loses all activity at pH 7, so that it could not function in an acidic environment. Since the passage tells us that pancreatic amylase functions in the small intestine, choice D must be incorrect.