Science Assessment Prompt

Course: Biology – Enzyme Catalyzed Reactions

 

Introduction – Below you will find some information that will help you get started with a research project.  Read the information carefully and think of a related research question that you would like to investigate.  Your job will be to design and conduct an experimental research project to answer this question and write a report of your findings.  There are six parts to your report. 

 

Research Question / Hypothesis – A statement of what question you will investigate and your “educated prediction” about what you will find out through an experiment.

Literature Review – A description of what information you have found out about the research question through reading books, magazines, personal interviews or web-sites.

Experimental Procedure – A step by step, repeatable description of how you will conduct your experiment to answer your research questions.

Results / Data – Tables that contain the data you collect.

Analysis – Graphs or statistical calculations you have created to make your data more meaningful.

Conclusions – A description of what you found out by doing your experiment.  Include whether your hypothesis was found to be correct or incorrect, and what new directions you would investigate next to improve your experiment or answer new questions that arise.

 

The six parts of your research paper and how your responses to them will be evaluated are described in more detail in the rubric that your teacher will share with you.

 

Enzyme Catalyzed Reactions

 

Figure 1.  3D structure of Catalase from E. Coli

 

Basic Information for Literature Review – Catalysts are molecules which speed the rate of reactions.  Enzymes are special types of protein chemicals which act as catalysts for biological reactions.  Enzymes can be found in all living things, plant and animal. In this activity you will investigate some of the properties of chemical reaction that is helped along by an enzyme.  The enzyme used in this investigation is called catalase.  Catalase is produced by the body to break down Hydrogen peroxide (H2O2).

 

Hydrogen peroxide (H2O2) is a common by-product of metabolic reactions. In high concentration it is toxic; therefore, its accumulation in cells would be harmful. Most tissues, however, contain the enzyme catalase, which catalyzes the breakdown of peroxide to water and oxygen as follows:

 

SUBSTRATE            ENZYME                 PRODUCTS

 

  2 H2O2              Catalase      --->    2 H2O  + O2  + heat

 

The reaction is extremely rapid. The action of the enzyme can be demonstrated easily by the evolution of oxygen in the form of gas bubbles when an extract of a tissue containing the enzyme is added to a dilute solution of hydrogen peroxide. We will use homogenized (ground-up) liver or potato as a source of catalase.

 

The following paragraph is from an enzyme web site http://www.facstaff.bucknell.edu/toner/gb/lab121/labs34.html) but it explains the relationship between enzyme activity and temperature very well:

 

All chemical reactions speed up as temperature is raised. As the temperature increases, more molecules have enough kinetic energy to undergo the reaction. Since enzymes are catalysts for chemical reactions, enzyme reactions also tend to proceed faster with increasing temperature. However,

if the temperature of an enzyme-catalyzed reaction is raised still further, an optimum is reached: above this point, the kinetic energy of the enzyme and water molecules is so great that the structure of the enzyme molecules starts to be disrupted. The change in structure of a protein molecule accompanied by the destruction of the active ability of a protein is called denaturing.  At a certain temperature, the positive effect of speeding up the reaction is now more than offset by the negative effect of denaturing more and more enzyme molecules.  Many proteins are denatured by temperatures around 40-50deg.C, but some are still active at 70-80deg.C, and a few even withstand being boiled.

 

Different enzymes have different optimum temperatures, depending on the organism and environment they have evolved in.  The same enzyme can also have different optimum temperatures depending on it's source.  As an example, a certain reference for a plant catalase indicates that it has an optimum temperature of 40 deg. C and an operating range of 0-50 deg. C.  

 

You should design an investigation that will examine the effects of some variable on the rate of a reaction between the catalase found in liver or potato and Hydrogen peroxide.

 

 

Standards, Benchmarks and Indicators –

 

Standard 1 – Science as Inquiry - Formulate research questions, conduct experimental investigations, analyze data, use appropriate technology, communicate results, defend conclusions, and propose further investigations.

 

Standard 3 – Life Science – Analyze the characteristics, structure, and processes of living systems (e. g., molecular, organism, populations) and describe how living systems interact with each other and their environment.

 

Biology Life Science Benchmark

Analyze factors and predict results of interactions between living organisms and their environment.

 

Material Requirements – .Liver extract (prepared by teacher) or pieces, potato extract (prepared by teacher) or pieces, 3% Hydrogen Peroxide, test tubes, test tube racks, stopwatch, millimeter ruler, beakers or cups, disposable pipette.

 

Starting Points For the Experimental Procedure - Obtain some liver or potato extract and keep in an ice bath to maintain enzyme integrity.

Measure out 0.25 ml of extract and place in a clean test tube.

Set in test tube rack where the tube is clearly visible.

Measure out 1 ml of 3% hydrogen peroxide and place into another test tube.

Into this same test tube add 1ml of distilled water.

Have a ruler and watch handy. Be prepared to measure the height of the froth and time   

the movement as soon as the tubes re mixed.

Pour the peroxide into the liver extract tube and immediately begin timing and measure

the distance from the bottom of the tube to the line of maximum height. If the froth overflows the tube or if the reaction proceeds too quickly, dilute your liver extract with some distilled water and repeat.

The actual height of the froth is the height reached during the reaction minus the starting height of the solution. To determine the starting height of the solution pour 2.2.5 ml of water into an empty test tube and measure this height.

 

Rate= height of froth above starting height/ time taken to reach that height

 

Using the technique above to measure the speed of the catalase reaction you should be able to design an experiment to measure the effects of a variable you wish to investigate on the rate of reaction.

 

Cautions / Laboratory Safety – Hydrogen Peroxide is a caustic solution.  Students should wear goggles when using Hydrogen Peroxide.