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Enzymes are Most Effective at Optimal Conditions enzyme may even stop functioning completely. Enzymes typically work best under certain narrowly defined conditions, such as temperature, pH, and ion concentration. Changing these alter the rate of reaction caused by the enzyme. In nature, organisms adjust the conditions of their enzymes to produce an optimum rate of reaction, where necessary, or they may have enzymes which are adapted to function well in extreme conditions where they live. All enzymes have an optimal temperature in which they work the best. The rate of the reaction increases with rise in temperature (fig. 1a). This is because the heat enhances the kinetic energy of the enzyme and substrate molecules which results in more number of collisions between the substrate and active site. On the other hand, in low temperature conditions, the reaction becomes slow as there is less contact between the substrate and the enzyme. However, extreme temperatures are not good for the enzymes. Under the influence of very high temperature, the weak H-bonds of the enzyme tend to break, due to which the rate of reaction decreases or stops all together. In other words, a denatured enzyme fails to carry out its normal functions. In the human body, the optimum temperature at which most enzymes become highly active lies in the range of 95°F to 104°F (35°C to 40°C). There are some enzymes that prefer a lower temperature than this. The efficiency of an enzyme is largely influenced by the pH value of its surroundings. This is because the charge of its component amino acids changes with the change in the pH value. Each enzyme becomes active at a certain pH level. In general, most enzymes remain stable and work well in the pH range of 6 and 8 (fig. 1b). However, there are some specific enzymes which work well only in acidic or basic surroundings. The favorable pH value for a specific enzyme actually depends on the biological system in which it is working. When the pH value becomes very high the OH- groups removes H+ ions and causes H-bonds in the protein to break and the enzyme denatures. Or, when the pH is too low, the H+ ions can also cause the H-bonds to break and the enzyme to denature. As a result, the active site of the enzyme fails to bind well with the substrate properly and the rate of reaction decreases. The Substrate concentration plays a major role in various enzyme activities. This is because a higher concentration of substrate means it takes less time for substrate molecules to collide with the active site of the enzyme and the reaction rate increases (fig. 2b). Whereas, a low concentration of substrate means it takes longer for substrate molecules to collide with the active site of the enzyme and the reaction rate decreases. When the rate of an enzymatic reaction is at its maximum, an increase in the concentration of substrate will not make any difference in the enzyme activity. In this condition, the substrate is continuously replaced by new ones at the active site of the enzyme–the enzyme is working as fast as it can. In any enzymatic reaction, the amount of substrate molecules involved is usually more than the number of enzyme molecules. An increase in enzyme concentration will increase the enzyme reaction rate for the simple reason that more enzymes are participating in the reaction (fig. 2a). The rate of the reaction is directly proportional to the quantity of enzymes available for it. However, that does not mean that a constant rise in concentration of enzymes will lead to a steady rise in the rate of reaction. Rather, a very high concentration of enzymes where all the substrate molecules are already used up does not have any impact on the reaction rate. To be precise, once the rate of reaction has reached its maximum, an increase in the quantity of enzymes does not affect the rate of reaction anymore. Inhibitors are substances that have a tendency to prevent activities of the enzymes. Enzyme inhibitors interfere with the enzyme functions in two different ways (fig. 3). Based on this, they are divided into two categories: competitive inhibitors and noncompetitive inhibitors. A competitive inhibitor has a structure which is the same as that of a substrate molecule, and so it fits into the active site of the enzyme easily and restricts the substrate from attaching. This decreases the rate of the reaction. A noncompetitive inhibitor binds with the enzyme at a site other than the active site, the allosteric site. This causes the enzyme to change its shape, altering the shape of the active site. In this condition, the substrate molecule cannot bind itself to the active site and thus, the subsequent enzyme activities are blocked and no reactions can occur. Adapted from Mukherjee, Bidisha. (Nov. 16, 2011). “Important Factors That Influence Enzyme Activity”. (Retrieved October 9, 2013). http://www.buzzle.com/articles/important-factors-thatinfluence-enzyme-activity.html. Adapted from Solomon, Berg, and Martin. (1999). “Enzymes are th chemical regulators”. In: Biology, 5 ed., pp. 144-150. Harcourt, Inc. Fig. 1 retrieved October 9, 2013 enzyme_activity.html 08_18EnzymeEnvironFactors.jpg. Fig. 2 retrieved October 9, 2013 www.skinnersbiology.co.uk. Fig. 3 retrieved October 9, 2013 chemistry.tutorvista.com. Instructions for Reading Article Focus Question: How do different environmental conditions affect the rate of an enzymatic reaction? As you read… Number the paragraphs Circle the environmental conditions that affect enzymes Underline what the condition does to the enzyme—structure and function Box what the condition does to the rate of reaction After reading and discussing article, complete graphic organizer in Ch. 5 Enzyme packet. WU: Enzymes are Most Effective at Optimal Conditions Name _______________________ Date ______________ Per _____ Use the article from yesterday to answer the following questions. Answer using complete sentences where appropriate. 1. What is the optimal temperature range for most enzymes? _____________ Explain why most enzymes function best at these temperatures. _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ 2. What is the optimal temperature for the enzymes found in thermophilic bacteria? __________________ 3. Where in the article was this information found? ____________________________________________ _________________________________________________________________________________ 4. What does it mean to be thermophilic? ___________________________________________________ _________________________________________________________________________________ 5. Where in the article was this information found? ____________________________________________ _________________________________________________________________________________ 6. Why would the enzyme pepsin no longer function in digestion when it enters the small intestine? _________________________________________________________________________________ _________________________________________________________________________________ 7. Why will adding excess amounts of enzyme not continue to speed up the rate of reaction? _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ 8. Both a competitive inhibitor and a non-competitive inhibitor will decrease the rate of an enzymatic reaction. Explain the difference in how each inhibitor affects the enzyme’s ability to function. _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________ _________________________________________________________________________________