Enzymes and Cellular Regulation What are the factors that regulate the rate at which enzymes catalyze reactions? Why? Digestive enzymes are protein-based biological catalysts that play important roles in our lives. They help remove stains from our shirts, turn milk into cheese, and are responsible for turning our dinner into use able fuel for our bodies. Enzymes however do not work well universally. Some are meant to work at high temperatures, others at low temperatures. They may work best in acidic conditions or neutral conditions. In this activity we will look at the optimal conditions for two different enzymes. The digestive enzyme lipase is made in the pancreas and breaks down lipids in the small intestine, while pepsin breaks down proteins in the stomach. Model 1 – Two Digestive Enzymes Triglycerides glycerol + fatty acids Pepsin Large polypeptides smaller polypeptides + amino acids Effect of pH on Enzyme Activity Rate of reaction -Pepsin (stomach) – -Lipase 0 2 4 6 8 10 12 14 pH 1. Name the two enzymes illustrated in Model 1. 2. Consider the information provided in the Why? box and in Model 1 about these proteins. a. In which body organ is pepsin active? b. In which body organ is pancreatic lipase active? 3. For each enzyme in Model 1, circle the pH that best represents the environment in which the enzyme is most active. Pepsin 5 1. 1.5 8 10.4 Lipase 1.5 10.4 4. Compare the rate of the pepsin-catalyzed reaction at pH 1.5 with the rate of the lipase-catalyzed reaction at pH 1.5. 5. Compare the rate of the pepsin-catalyzed reaction at pH 8 with the rate of the lipase-catalyzed reaction at pH 8. 6. Using your knowledge of protein structure, explain in detail the effect of exposing an enzyme to a pH outside of its optimal range. Include the effect on both enzyme structure and function. 7. At what pH values is lipase likely to be denatured? Justify your answer. 8. At what pH values is pepsin likely to be denatured? Justify your answer. 9. In addition to being produced in the pancreas, lipase is also produced in the stomach. Is the structure of pancreatic lipase the same as gastric (produced in the stomach) lipase? Justify your reasoning 10. Add a line to the graph in Model 1 that shows a prediction for gastric lipase activity. 11. Antacids work by neutralizing acids, bringing the pH of the stomach to a range of 6-7. What is the effect of taking an antacid on a person’s ability to digest proteins?
The Correct Answer and Explanation is :
Correct Answers:
- The two enzymes illustrated in Model 1 are:
- Pepsin: A digestive enzyme that breaks down proteins in the stomach.
- Lipase: A digestive enzyme that breaks down lipids in the small intestine.
- Consider the information provided:
a. Pepsin is active in the stomach. It functions optimally in acidic conditions, which are present in the stomach due to gastric juices.
b. Pancreatic lipase is active in the small intestine. It functions best in neutral or slightly alkaline conditions, which are found in the small intestine due to bile and pancreatic secretions. - Optimal pH for each enzyme:
- Pepsin is most active at pH 1.5, which reflects the acidic environment of the stomach.
- Lipase is most active at pH 10.4, indicating that it functions best in the more alkaline environment of the small intestine.
- Comparison of reaction rates at pH 1.5:
- At pH 1.5, pepsin has a higher rate of reaction than lipase because pepsin is adapted to function in the acidic stomach environment, while lipase requires a more neutral or alkaline pH to function effectively.
- Comparison of reaction rates at pH 8:
- At pH 8, lipase performs better than pepsin. Lipase is active in neutral to slightly alkaline conditions, while pepsin works best in acidic conditions, so its activity drops at pH 8.
- Effect of pH on enzyme structure and function:
- Enzymes are proteins, and their function is highly dependent on their 3D structure, which is held together by weak bonds like hydrogen bonds and ionic interactions. A pH outside an enzyme’s optimal range can disrupt these interactions. If the pH is too acidic or too basic, the enzyme’s structure can change (denaturation), leading to a loss of function. This is because changes in pH can alter the charge on amino acids involved in the enzyme’s active site, preventing proper binding with substrates.
- Lipase denaturation pH:
- Lipase is likely to be denatured at pH values below 4 and above 10. This is because lipase functions optimally in the slightly alkaline conditions of the small intestine (around pH 8), and exposure to highly acidic or strongly alkaline environments can alter its structure.
- Pepsin denaturation pH:
- Pepsin is likely to be denatured at pH values above 4-5, as it functions best in the highly acidic environment of the stomach (pH 1.5). At higher pH values, its active site may change, reducing its activity.
- Pancreatic lipase vs. gastric lipase structure:
- Pancreatic lipase and gastric lipase are not identical. While both enzymes break down lipids, they are adapted to work in different pH environments. Pancreatic lipase is adapted to the neutral to slightly alkaline environment of the small intestine, while gastric lipase functions in the acidic environment of the stomach. Their structures may differ to accommodate these distinct pH ranges.
- Prediction for gastric lipase activity:
- Gastric lipase would likely have a peak of activity around pH 4-5, which is the typical pH of the stomach. The graph would show a higher rate of reaction at this pH, similar to pepsin.
- Effect of antacids on protein digestion:
- Antacids neutralize stomach acid, raising the pH of the stomach to around 6-7. Since pepsin works optimally in the acidic conditions of the stomach (around pH 1.5), neutralizing stomach acid can reduce pepsin’s ability to digest proteins effectively. This can impair protein digestion, as pepsin requires an acidic environment to maintain its active form.
300-Word Explanation:
Enzymes are highly specialized proteins that act as biological catalysts, speeding up chemical reactions by lowering the activation energy required. The rate at which enzymes catalyze reactions is influenced by factors such as pH, temperature, substrate concentration, and enzyme concentration. Enzymes are typically adapted to function best under specific conditions, and these conditions are often tied to the environment where the enzyme operates.
In the digestive system, enzymes like pepsin and lipase work in very different environments. Pepsin, which breaks down proteins in the stomach, operates in the acidic environment (pH ~1.5) of the stomach. Its structure is specifically adapted to function optimally under low pH. In contrast, lipase, which breaks down lipids in the small intestine, functions best in slightly alkaline conditions (pH ~10.4).
Enzyme activity is highly sensitive to pH. Each enzyme has an optimal pH range where it functions most efficiently. For example, pepsin is denatured (loses its function) at higher pH values because the altered charge on its amino acids disrupts the active site. Likewise, lipase becomes inactive in highly acidic conditions. Denaturation occurs because the enzyme’s tertiary structure is altered when the pH moves away from its optimal range.
Antacids, which neutralize stomach acid, can raise the pH of the stomach, which reduces the effectiveness of pepsin in digesting proteins. This illustrates how important the acidic environment is for protein digestion in the stomach. By altering this environment, antacids can impair digestive efficiency.