Download Toothpickase Lab

TOOTHPICKASE
MODELING ENZYMATIC REACTIONS
INTRODUCTION
Energy in Chemical Reactions:
In chemical reactions, energy is absorbed or released when chemical bonds are broken and new ones
are formed.
Metabolism = all of the chemical reactions that occur within an organism.
Your cells get most of the energy needed for metabolism from the food you eat.
As food is digested, chemical reactions convert the chemical energy in food molecules to forms of
energy that can be used by cells.
Activation Energy:
Activation energy = the energy needed to start a chemical reaction.
Activation energy is simply a chemical “push” (like pushing a rock) that starts a chemical reaction.
Enzymes:
Cells consume fuel because they need energy to function.
Most biochemical reactions – chemical reactions that occur in cells – require activation energy to begin.
The chemical reactions in cells occur quickly and at relatively low temperatures because of enzymes.
Enzymes = substances that increase the speed of chemical reactions.
Most enzymes are proteins.
Enzymes are catalysts.
Catalysts = substances that reduce the activation energy of a chemical reaction.
An enzyme increases the speed of a chemical reaction by reducing the activation energy of the reaction.
Enzymes help organisms maintain homeostasis.
Without enzymes, chemical reactions would not occur quickly enough to sustain life.
For example, consider a reaction that takes place in your blood.
Blood carries carbon dioxide, CO2, (a waste product made by cells) to your lungs, where it is eliminated
as you breathe out.
In the lungs, carbon dioxide reacts with water, H2O, to form carbonic acid, H2CO3:
CO2 + H2O  H2CO3
Assisted by carbonic anhydrase
The reverse reaction occurs in your lungs, converting carbonic acid back to carbon dioxide and water.
CO2 + H2O  H2CO3
Assisted by carbonic anhydrase
Most enzyme-assisted reactions are reversible, meaning they can proceed in the opposite direction.
Without an enzyme, the reaction that produces carbonic acid is very slow (2000/hour).
This rate is not fast enough for your blood to carry away the carbon dioxide.
Blood contains the enzyme “carbonic anhydrase”.
Allows 600,000 carbonic acid molecules per second.
Increases the reaction rate about one million times enabling your body to eliminate carbon dioxide
efficiently.
Enzyme Specificity:
Substrate = a substance on which an enzyme acts during a chemical reaction.
Enzymes act only on specific substrates.
For example: The enzyme amylase assists in the breakdown of starch to glucose.
Starch  Glucose
with the aid of amylase
Starch  Glucose
with the aid of amylase
Starch is amylase’s substrate.
Catalase assists in the breakdown of hydrogen peroxide (H2O2) which is a toxin formed in cells.
2H2O2  2H2O + O2 with the aid of catalase (Reversible also)
Hydrogen peroxide is catalase’s substrate.
An enzyme’s shape determines its activity.
Typically, an enzyme is a large protein with one or more deep folds on its surface.
Active site = the fold/pocket where an enzyme’s substrate fits into.
An enzyme acts only on a specific substrate because only that substrate fits into its active site.
Three steps of enzyme activity:
1. A substrate attaches to an enzyme’s active site.
2. The enzyme reduces the activation energy of the reaction.
3. New products are formed. The enzyme is not changed by the reaction and free to catalyze
further reactions.
Factors in Enzyme Activity:
Any factor that changes the shape of an enzyme can affect the enzyme’s activity.
For example, enzymes operate most efficiently within a certain range of temperatures.
Temperature outside this range can either break or strengthen some of the enzyme’s bonds, changing
its shape.
Enzymes also operate best within a certain range of pH values.
A pH value outside this range can cause bonds in an enzyme to break, reducing the enzyme’s
effectiveness.
The enzymes that are active at any one time in a cell determine what happens in that cell.
Your body’s cells contain many different enzymes, and each enzyme catalyzes a different chemical
reaction.
Different kinds of cells contain different collections of enzymes.
PURPOSE
In this activity, you will be modeling an enzyme reaction using your hands as the enzyme (toothpickase)
and toothpicks as the substrate.
PROCEDURES
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
Divide your toothpicks into five piles of 40 toothpicks each.
Add 10 colored toothpicks into each of your piles.
Move one pile of toothpicks in front of you and push the other piles off to the side.
Choose one person to represent the enzyme and the other person to be the recorder/time
keeper.
The person representing the enzyme (picking toothpicks) will need to look straight ahead.
For 10 seconds, you will pick-up toothpicks, place them between your thumb and forefinger of
both hands and bring them up to face level (you must see them and you are looking straight
ahead).
If they are the correct toothpick (see step #9), you will break them in half.
After breaking them, you will return both halves to the pile of toothpicks in front of you.
Two stipulations to breaking toothpicks:
a. If you pick-up an already broken toothpick, you CANNOT break it and it must go back
into the pile.
b. If you pick-up a colored toothpick, you CANNOT break it and it must go back into the
pile.
At the 10 second mark, your partner will say “stop” and you will count the number of toothpicks
broken and record this number in the data table.
Repeat steps 5-10 for 30, 60, 120, and 180 second intervals.
DATA RECORDING
Data Table
Time (sec)
# Toothpicks
Graph
0
10
30
60
120
180
DATA ANALYSIS
Calculate the rates of reaction between time intervals using the following equation:
M2-M1
T2-T1
M = Toothpicks T = Time 2 = Final
1 = Initial
Time (sec)
Rate of
Reaction
0
10
30
60
120
180
CONCLUSION
1. What was the name of the enzyme involved in this reaction?
2. What was the name of the substrate involved in this reaction?
3. With reference to enzyme structure, what part of an enzyme did your thumbs and forefingers
represent?
4. What did the colored toothpicks represent?
5. Write a conclusion statement about the enzymatic rate of reaction in this model.
6. What do you think would have happened to the reaction rate if the enzyme was exposed to the
following conditions:
a. Warm temperatures (a bit warmer than the room)
b. Cold temperatures (refrigerator temp)
c. pH of 2