Enzymatic Activity (Kevin Bugg)

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Title: Enzymatic Activity

Principle(s) Investigated: Catalysis, Enzymatic Activity

Standards:

Biology/Life Sciences Grades 9-12

Cell Biology

1. The fundamental life processes of plants and animals depend on a variety of chemical reactions that occur in specialized areas of the organism’s cells. As a basis for understanding this concept:

b. Students know enzymes are proteins that catalyze biochemical reactions without altering the reaction equilibrium and the activities of enzymes depend on the temperature, ionic conditions, and the pH of the surroundings.

Chemistry Grades 9-12

Conservation of Matter and Stoichiometry

2. The conservation of atoms in chemical reactions leads to the principle of conservation of matter and the ability to calculate the mass of products and reactants. As a basis for understanding this concept:

a. Students know how to describe chemical reactants by writing balanced equations.

Materials:

- Four clear plastic cups (9 oz.)

- Four small paper cups (3.5 oz.)

- Bottle 3% hydrogen peroxide (H2O2)

- Yeast (Fleischmann’s Active Dry Yeast)

- Raw potato

- Raw chicken liver

- Knife

- Cheese grater

- Permanent marker

Procedure:

1. You are given a suspension of catalase enzyme that has come from either an arctic fish or a tropical bird. Explain how would you set up an experiment to identify the source organism and explain your rationale. What results do you expect to see?

Catalase is found in most organisms that utilize oxygen in cellular respiration. Because there is a wide range of ecosystems in which organisms live, their metabolic activities must be optimized for the particular environment. Arctic fish live in a much colder environment than tropical birds. Therefore, the catalase isolated from such an organism would have a much lower optimal temperature than would catalase isolated from the tropical bird.

An experiment could be devised wherein the experimental variable is temperature. Enzymatic activity could be measured either qualitatively (visual) or quantitatively (oxygen probe) at different temperatures to assess its functional range and peak activity temperature.

2. An experiment is devised wherein upon completion of an enzymatic reaction the color of the solution changes. Ten beakers are set up where each successive one has double the enzyme concentration of the last (i.e. .5 M, 1 M, 2 M, etc.). Into the first beaker you pour a specified amount of substrate and measure how long it takes for the beaker to change color. You repeat this measurement of each of the other beakers using the same amount of substrate as the first. You find that for the first several beakers, time decreases, but for the last several beakers, there is no significant change in reaction time. Explain these data.

In the first several beakers, an increase in the concentration of enzyme increases the rate of the reaction. Conceptually, the enzyme is the “rate limiter”. In the first beaker, the reaction rate is the lowest (time is longest) because there are very few enzymes in relation to substrate and they have to go from molecule to molecule of substrate to catalyze the reaction. The ratio of substrate to enzyme is high so each enzyme has a lot of work to do relatively speaking. In subsequent beakers, the ratio decreases, each enzyme has less work to do, and the job gets done faster.

There comes a point, however where the substrate to enzyme ratio is reduced to 1:1. It is at this point that reaction rate is fastest. The addition of more enzymes will not increase the rate. An enzyme is already acting upon each molecule of substrate. Additional enzymes have no work to do.

3. It is a general chemistry principal that reaction rate is directly related to temperature. As temperature increases, so does the reaction rate. Why, then, don’t enzymatic reaction rates continue to increase as temperature increases?

Temperature is a measure of the average kinetic energy (motion) of matter. In the absence of a biological catalyst, increases in the movement of reactant molecules increases the chance (frequency) of them colliding with each other and forming the products of the reaction. Additionally, increased temperature provides activation energy to the chemical reaction.

Biochemical reactions require enzymes that are not a part of the reactions itself, but catalyze them. Enzymes have optimal temperatures representative of the organism from which they come. Excessive temperature alters protein (enzyme) conformation, called denaturation, which destroys the enzymes functionality. The weak interactions essential to the enzyme’s structure are overcome by the kinetic energy of the atoms in the molecule as temperature increases.

Applications to Everyday Life:

1. Cleaning products, like laundry detergents, contain enzymes. These enzymes aid in the removal of protein, sugar and lipid stains on clothing. Without these enzymes, some stains would be difficult to remove.

2. pH equilibrium in the human body is maintained with the help of enzymes. The main pH buffer system involves the conversion of bicarbonate, produced from dissolved carbon dioxide in the blood, into carbonic acid, and vise versa. Enzymes help speed this conversion between these two molecules so that the body can quickly respond to changes in blood pH.

3. Water treatment facilities use bacteria and/or microbial enzymes to treat sewage water. Whether whole bacteria are used or relevant enzymes are extracted and used, the principle of biochemical catalysis is exemplified as biological waste is decomposed and separated from the water.

Photographs: Include a photograph of you or students performing the experiment/demonstration, and a close-up, easy to interpret photograph of the activity --these can be included later.

Videos:

1. Catalyzed chemical reaction 1

2. Catalyzed chemical reaction 2

Resources:

Interview (Live Demonstration Workshop)

(N. Withers, Enzymatic Activity of Catalase Lab, October 7, 2011)