Chemical reactions and enzymes

Section 2

Section 2 Vocabulary: ( 6 words)

1. chemical reaction (reactants, products),

2. activation energy,

3. catalyst,

4. enzyme,

5. substrate,

6. active site.

SC.912.L.18.11

• Explain the role of enzymes as catalysts that lower the activation energy of biochemical reactions.

• Identify factors, such as pH and temperature, and their effect on enzyme activity.

Energy is the ability to cause change

•Mechanical Energy

•Thermal Energy

•Chemical Energy

•Light Energy

•Sound Energy

•Electrical Energy

Thermodynamics: the study of energy transformation

First Law of Thermodynamics: Energy cannot be created or destroyed; it can only be converted from one form to another

•Using food for movement

•Using food for maintaining body temperature

•*Usable energy decreases as some is transferred to heat.

Energy can be stored or released by chemical reactions.

Chemical Equations

•Reactants: substances that are combined or broken apart

•Products: new substances that are formed

•REACTANTS PRODUCTS

Some reactions give off energy ( heat)Exergonic. The amount of energy is less at the end due to heat beingreleased.

and some take it inEndergonic! The amount of energy is greater at the end! Heat is taken in!These reactions require energy to occur!

Energy releasing

Energy storing

The number before each chemical formula represents the number of molecules. The subscripts indicate the number of atoms of each

element.A chemical equation is

balanced when the numbers of atoms of each element are

equal on each side of the arrow.

2H2 + O2 2H2O

RespirationThe chemical reaction that living things use to take glucoseAnd oxygen and release the energy Stored in the chemical bondsAnd form ATP molecules while producingWater and carbon dioxide as products!

1. Write the chemical reaction for respiration

2. Circle the reactants and box the products in the above reaction

.3. In a balanced equation, How many molecules of glucose are used in this reaction? ONE How many molecules of oxygen are used? six

•Activation Energy: energy needed to start a chemical reaction

•Gasoline doesn’t burn on its own…it needs a spark

4. What is activation energy?

energy needed to start a chemical reaction

Enzymes Lower the activation energy!

•Enzymes provide activation energy for the biochemical reactions in cells.

•Enzymes are catalysts—they increase the rate of reactions at lower temperatures by lowering the activation energy needed.

Words that end in –ASE are enzymes.

enzymes

•Substrate: molecule to which an enzyme binds

•Active site: place on enzyme where substrate binds.

• Example: Amylase catalyzes the breakdown of starch into glucose.

• Enzymes attach only to certain molecules.

• pH and temperature affect the shape of an enzyme.

• 5. Factors that might affect the rate of an enzyme catalyzed reaction include what?

• Temperature, pH, concentrations of the enzyme and substrate

• Anything that alters the shape of the enzyme so that the substrate can’t fit into the active site or the availability of the enzyme.

• 6. What does changing the pH do to an enzyme? It can break bonds between the chains of amino acids and the shape of the protein can be changed so that the active site is no longer open for bonding the substrate! This denatures the enzyme!

• 7. Changing the temperature? Can do the same as pH it can break the hydrogen bonds that hole a protein in the proper shape and denature the enzyme!

• 8. The major role of an enzyme in biochemical reactions is what?

• They lower the energy of activation! This allows chemical reactions to take place at greater rates and lower temperatures.

• 9. What is the active site of an enzyme?

• The place on the enzyme where the substrate binds!

an enzyme: protein that lowers the activation energy! Catalyst!

• 10. Draw a graph of an enzyme catalyzed reaction and a reaction without

BIOLOGY LAB:

• Title: The Enzyme CATALASE

• INTRODUCTION:

• What would happen to your cells if they made a poisonous chemical?

• You might think that they would die.

• In fact, your cells are always making poisonous chemicals. They do not die because your cells use enzymes to break down these poisonous chemicals into harmless substances.

• Enzymes are proteins that speed up the rate of reactions that would otherwise happen more slowly.

• The enzyme is not altered by the reaction.

• You have hundreds of different enzymes in each of your cells. Each of these enzymes is responsible for one particular reaction that occurs in the cell.

• In this lab, you will study an enzyme that is found in the cells of many living tissues.

• The name of the enzyme is catalase (KAT-uh-LAYSS);

• it speeds up a reaction which breaks down hydrogen peroxide, a toxic chemical, into 2 harmless substances--water and oxygen.

• The reaction is as follows:

• 2H2O2 ----> 2H2O + O2

• This reaction is important to cells because hydrogen peroxide (H2O2) is produced as a byproduct of many normal cellular reactions.

• If the cells did not break down the hydrogen peroxide, they would be poisoned and die.

• In this lab, you will study the catalase found in liver cells.

• You will be using chicken or beef liver. It might seem strange to use dead cells to study the function of enzymes.

• This is possible because when a cell dies, the enzymes remain intact and active for several weeks, as long as the tissue is kept refrigerated.

Problems:write these down

1. What living materials contain catalase?

2. Is catalase used up in the reaction?

3. What happens to the rate of the catalase reaction when the temperature and pH levels are raised/lowered?

4. How does crushing/cutting up the material affect the rate of the reaction?

PRELAB REVIEW: • Before you begin this lab, review pH.

Recall that pH is the measure of the acidity or alkalinity of a solution.

• An acidic solution has many hydrogen ions (H+) and a pH below 7.

• An alkaline, or basic, solution has very few hydrogen ions and a pH above 7.

• A neutral solution has a pH of 7.

• Recall that the substrate is the molecule that the enzyme acts on, and the products are the molecules produced by the reaction. Review that enzymes are reusable because they are not part of the reaction!

denatured• Under certain conditions enzymes are

denatured.

• An enzyme is denatured when the protein molecule loses its proper shape and cannot function.

• Some things that can denature an enzyme are high temperatures, extremes of pH, heavy metals, and alcohol.

MATERIALS: 1 acetic acid (vinegar) (in dropper bottle)1 sodium bi carbonate base (baking soda solution) (in dropper bottle)6 Test tubes and rackTest tube holder10-ml Graduated cylinder40 ml 3% Hydrogen peroxide solutionScalpel 3 beakers for water bathsScissors and Forceps (tweezers)ThermometerStirring rodpH paperFresh liver, chicken meat, Apple, and Potato

Hypotheses:write these down!

• Make your own hypothesis for each of the problems for this lab! Write them in the same order as the original problems!

• Example; Problem number 2: This researcher believes the catalase will not be used in the reaction.

• There will be a hypothesis for each of the 4 problems!

• 1. It is hypothesized that liver, chicken, apple and potato will or will not contain catalase? Make a hypothesis for each substance!! And then in your conclusion, did you accept or reject each one?

• 2. It is hypothesized that catalase will or will not be used up in the reaction.

• 3. 1. When the temperature is raised above room

temperature the rate of the reaction will…

2. When the temperature of the reaction is lowered below room temperature the rate will…

3. When the pH is 7 the rate will …

4. When the pH is below 7 the rate will be…

5. When the pH is above 7 the rate will be …

4. Crushing the samples will __________ the rate of the reaction.

• Throughout this investigation you will estimate the rate of the reaction (how rapidly the solution bubbles) on a scale of 0-5 (0=no reaction, 1=slow, 5= very fast).

• Use the height on the test tube to help estimate the rate of the reaction.

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PROCEDURE:

• Part I Normal Catalase ActivityNOTE: Be sure to clean your stirring rod (and test tubes) between steps. Wash all test tubes before using!!

• 1. Place 2 ml of the 3% hydrogen peroxide solution into a clean test tube.

• 2. Using forceps and scissors cut a small piece of liver and add it to the test tube.

• NEW!!! Measure the mass of the piece of liver so you can cut pieces approximately the same size each time!!! Push it into the hydrogen peroxide with a stirring rod. Assume that the reaction in step 2 proceeded at a rate of "4" and record the speed in DATA TABLE 1, and DATA TABLE 2 as the rate at room temperature.

• Observe the bubbles; what gas is being released? No place on the answer sheet for this!

• 3. Recall that a reaction that absorbs heat is endothermic; a reaction that gives off heat is exothermic. Now, feel the temperature of the test tube with your hand. Measure the temperature with the probe if you want!

• 1. Has it gotten warmer or colder? Is the reaction endothermic or exothermic? How do you know?

Is Catalase Reusable? • 4. Place 2 ml of 3% hydrogen peroxide

solution into a clean test tube and add a small piece of liver. – 2. What is happening in your test tube?

• 5. Pour off the liquid into a second test tube.

• Assuming the reaction is complete. – 3. What is this liquid composed of? What do you

think would happen if you added more liver to this liquid? Why?

• 6. Add another 2 ml of hydrogen peroxide to the liver remaining in the first test tube. – 4. Can you observe a reaction? What do you

think would happen if you poured off this liquid and added more hydrogen peroxide to the remaining liver?

– 5. Are enzymes reusable?

Occurrence of Catalase • Catalase is present in many kinds of living

tissues. You will now test for the presence of catalase in tissues other than liver.

• 7. Place 2 ml of hydrogen peroxide in each of 3 clean test tubes. To the first tube, add a small piece of potato. To the second tube, add a small piece of chicken. To the last tube, add a small piece of apple. As you add each test substance, record the reaction rate (0-5) for each tube in TABLE 1. – 6. Which tissues contained catalase?

• Cut pieces of all of the items in the first part (the same size), mash one or cut it up. Place them each in test tube with 2 ml of hydrogen peroxide and record the reaction rates on the chart

Sample Whole size sampleRate of Enzyme Activity 0-5 scale

Crushed/ cut sampleRate of Enzyme Activity 0-5 scale

liver

potato

chicken

apple

Part II Effect of Temperature on Catalase Activity

• 8. Put a piece of liver into the bottom of a clean test tube and cover it with a small amount of water. Place this test tube in a boiling water bath for 5 minutes.

• 7. What will boiling do to an enzyme?

• 9. Remove the test tube from the hot water bath, allow it to air cool, then pour out the water. Add 2 ml of hydrogen peroxide. CAUTION: Use a test-tube holder when handling the hot test tubes.

• 8. What is happening in the test tube?

• Record the reaction rate (0-5) in DATA TABLE 2.

Temperature Rate of Enzyme Activity 0-5

0 OC_

Room Temp 24 OC

37 OC

100 OC

• 10. Put equal quantities of liver into 2 clean test tubes and 2 ml H2O2 into 2 other test tubes. Put one test tube of liver and one of H2O2 into each of the following water baths: Ice bath (0 deg.C) and Warm water bath (37 deg.C) (make the 37 deg by adding the hot water to room temp. water until it reaches 37 degrees)

• Use a temperature probe to record the actual temperature when the reaction takes place.

• 11. After 3 minutes, pour each tube of H2O2 into the corresponding tube of liver and observe the reaction. Record the reaction rates (0-5) in DATA TABLE 2. You recorded the reaction rate for room temperature earlier.

Temperature Rate of Enzyme Activity 0-5

0 OC_

Room Temp 24 OC

37 OC

100 OC

– 9. What is the "optimum" temperature for catalase? (This is the temperature at which the reaction proceeds fastest.)

– Why did the reaction proceed slowly at 0 OC? Why did the reaction not proceed at all at 100 OC?

Effect of pH on Catalase Activity

• 12. Add 2 ml Hydrogen peroxide to each of 3 clean test tubes. Treat each tube as follows:

• Tube 1--add a drop of acetic acid (acid) at a time until pH 3.

• Tube 2--add a drop of sodium bi carbonate base (base) at a time until pH 10.( you may not be able to reach 10..)

• Tube 3--adjust the pH to 7 by adding single drops of either acetic acid or sodium bi carbonate base as needed.

• CAUTION: Do not let acids or bases contact your skin or clothing. Swirl each test tube after adding each drop and measure the pH of each solution with pH paper. To do this, remove a drop or two of solution from a test tube using a clean glass stirring rod. Rinse your stirring rod and wipe dry before you dip it into each test tube. Place the drop on pH paper. Record the pH of each solution in DATA TABLE 3.

• 13. Next, add a small piece of liver to each test tube. Estimate the reaction rates (0-5) and record in DATA TABLE 3. – 10. Does there appear to be a pH "optimum"?

At what pH?– 11. What is the effect of low or high pH on

enzyme activity?

pH/Sample Rate of Enzyme Activity (0-5)

Conclusion: • Write a conclusion to the lab.

• 1. Go back and answer all of the original problems.

• 2. Use actual data to support your statements.

• 3. Accept or reject your hypotheses.

• 4. Use background data to help support your statements.

• 5. By reading your conclusion the reader should know the results of your experiment without having to look at the data charts. You may refer to the graphs when you make a statement, but give the actual data in your conclusion. Sum up the data so it tells the complete story.

• 6. Use the questions in the data section to help guide you towards what is important to learn about enzymes and tell about this in your conclusion.

• 7. Explain about any possible errors that might have caused your results to not be accurate. (Everyone should have something here!)

• 8. Get to the point without writing too much, but do not leave out important information. The conclusion is one of the most important parts of the lab!!!

Grades: 90 points totalTitle: 1pt Problems: 4 pts Hypotheses: 11ptsGroup: Data page: 30 points and Graphs: 23Conclusion: 21 points