Laboratory 4 Enzyme Activity 2023 (3)

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Louisiana State University *

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100

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Biology

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Dec 6, 2023

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4-1 L ABORATORY 4 E NZYME A CTIVITY Objectives During this laboratory the student will be introduced to enzymes. Specific objectives include: 1) Explore the activity of the enzyme catalase. 2) Investigate the effect of enzyme concentration on reaction time. 3) Investigate the effect of substrate concentration on reaction time. Introduction An enzyme is often a protein that acts as a biological catalyst to speed up reactions by making them more energetically favorable. Enzymes are necessary because most of the reactions that occur are not energetically favorable and would only occur rarely without enzymes. An enzyme can be identified if the molecular name ends with the suffix “ - ase”, for example amylase, catalase, and invertase are all enzymes. The substance upon which an enzyme acts is known as a substrate . The results of an enzyme-controlled reaction are known as products . Figure 1. Activation Energy of for a Reaction

4-2 In order to achieve their function, enzymes arrange substrates in to the most ideal configuration. This is accomplished in the active site of the enzyme. These active sites are complementary in shape and charge to the characteristics of the substrates the enzyme is specific too. The “ Lock and Key Model ” has been produced to help explain enzyme specificity. Some enzymes have proofreading mechanisms to prevent production of products that may be inferior or deleterious in nature. Figure 2. Lock and Key Model of Enzyme Specificity Most enzyme-controlled reactions are known as either synthetic or degradative reactions. Synthetic ( anabolic ) reactions are ones in which the substrate, often small molecules, are joined together to form a larger molecule. Degradative ( catabolic ) reactions are ones in which the substrate, often a large molecule, is broken down (digested) in to smaller molecules. Enzymes, like most catalysts, are not consumed in their reactions, therefore enzymes can continue acting on their substrates without being destroyed. Enzymes can further be classified by the amount of energy that is released or used in the reaction, or the net change in free energy. Reactions that release more energy than they use are classified as exergonic . This means that the products have less free energy, or negative free energy, compared to the substrates. Exergonic reactions can occur spontaneously, but many that use enzymes also require the use of a small amount of energy to begin. Cellular respiration is an example of an exergonic reaction. Reactions that use more energy than they release are classified as endergonic . This means that the products have more free energy, or positive free energy, compared to the substrates. Endergonic reactions are ones that always require energy to begin. Photosynthesis is an example of an endergonic reaction that requires light energy from sunlight.

4-3 Figure 3. Exergonic and Endergonic Reactions Enzymes are adapted to characteristics of their environment they are often found in, such as pH and temperature. For example, the enzyme amylase that is found in our saliva works best at a neutral pH of 7, and the enzyme protease that is found in our stomachs works best at a low pH of 1-2. Furthermore, similar enzymes found in different organisms may work best at different temperatures. For example, human protease works best around 37 ºC and that of a deep-sea fish works best around 1 ºC. The reason that enzymes work best at a particular pH or temperature is because their structure is adapted to these environmental characteristics. Outside of these ideal environmental characteristics, enzymes change shape altering their ability to accept substrates and produce products. Furthermore, enzyme concentration, substrate concentration, and time are directly related to the amount of product produced. The enzyme catalase is found in organisms that require oxygen for cellular respiration. Hydrogen peroxide, H 2 O 2 , is a byproduct of cellular respiration that can be destructive to cells, their organelles, and their molecules. Catalase uses H 2 O 2 as a substrate and catalyzes H 2 O 2 degradation into the products of water and oxygen: 2H 2 O 2 → 2H 2 O + O 2 Notice in this chemical equation the numbers of hydrogen and oxygen atoms in the substrates and in the products are the same.

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