Chemical reactions and enzymes

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Chemical reactions and enzymes

• Section 2

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Section 2 Vocabulary ( 6 words)

• chemical reaction (reactants, products),
• activation energy,
• catalyst,
• enzyme,
• substrate,
• active site.

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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.

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Energy is the ability to cause change
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• Mechanical Energy
• Thermal Energy
• Chemical Energy
• Light Energy
• Sound Energy
• Electrical Energy

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Thermodynamics the study of energy
transformation
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• 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.

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Energy can be stored or released by chemical
reactions.
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• Chemical Equations
• Reactants substances that are combined or
  broken apart
• Products new substances that are formed
• REACTANTS ? PRODUCTS

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Some reactions give off energy ( heat) Exergonic.
The amount of energy is less at the end due to
heat being released. and some take it
in Endergonic! The amount of energy is greater at
the end! Heat is taken in! These reactions
require energy to occur!
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Energy storing
Energy releasing
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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
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Respiration The chemical reaction that living
things use to take glucose And oxygen and release
the energy Stored in the chemical bonds And form
ATP molecules while producing Water and carbon
dioxide as products!
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1. Write the chemical reaction for respiration
2. Circle the reactants and box the products in
the above reaction
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. 3. In a balanced equation, How many molecules
of glucose are used in this reaction? ONE
How many
molecules of oxygen are used? six
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• Activation Energy energy needed to start a
  chemical reaction
• Gasoline doesnt burn on its ownit needs a spark

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4. What is activation energy?
energy needed to start a chemical reaction
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Enzymes Lower the activation energy!
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• Enzymes provide activation energy for the
  biochemical reactions in cells.
• Enzymes are catalyststhey increase the rate of
  reactions at lower temperatures by lowering the
  activation energy needed.
• Words that end in ASE are enzymes.

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enzymes
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• Substrate molecule to which an enzyme binds
• Active site place on enzyme where substrate
  binds.

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• Example Amylase catalyzes the breakdown of
  starch into glucose.
• Enzymes attach only to certain molecules.

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• pH and temperature affect the shape of an enzyme.

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Cheese and enzymes

• http//www.nsf.gov/news/mmg/mmg_disp.cfm?med_id69
  374

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• 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 cant fit into the active site
  or the availability of the enzyme.

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• 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!

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• 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.

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• 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!

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

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BIOLOGY LAB

• Title The Enzyme CATALASE
  

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• 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.

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• 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.

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• 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 ----gt 2H2O O2

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• 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.

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• 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.

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Problemswrite these down

• What living materials contain catalase?
• Is catalase used up in the reaction?
• What happens to the rate of the catalase reaction
  when the temperature and pH levels are
  raised/lowered?
• How does crushing/cutting up the material affect
  the rate of the reaction?

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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.

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• 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!

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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.

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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
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Hypotheseswrite 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!

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• 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?

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• 2. It is hypothesized that catalase will or will
  not be used up in the reaction.
• 3.
• When the temperature is raised above room
  temperature the rate of the reaction will
• When the temperature of the reaction is lowered
  below room temperature the rate will
• When the pH is 7 the rate will
• When the pH is below 7 the rate will be
• When the pH is above 7 the rate will be
• 4. Crushing the samples will __________ the rate
  of the reaction.

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

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4
2
1
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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!!

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• 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.

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• 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?

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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?

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• 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?

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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?

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• 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 sample Rate of Enzyme Activity 0-5 scale Crushed/ cut sample Rate of Enzyme Activity 0-5 scale
liver
potato
chicken
apple
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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?

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• 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
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• 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.

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• 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
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• 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?

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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.

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• 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.

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• 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)



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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.

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• 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.

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• 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!!!

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Grades 90 points total Title 1pt Problems 4
pts Hypotheses 11pts Group Data page 30
points and Graphs 23 Conclusion 21 points
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