INTRO TO ENZYMES
Chemical reactions change substances into different substances by breaking and forming chemical bonds.
Reactants are the substances that are changed during a chemical reaction.
Products are the substances made by a chemical reaction.
Label the reactants and products in the following chemical reactions:
2H2O2 ->
H2O + O2
AND
H2O + O2 -> 2H2O2
Bonds between atoms STORE energy, and when they are broken, bonds release energy.
Circle the above reaction in which energy is released when bonds are broken between atoms.
Put a star next the above reaction in which energy is needed to form bonds between atoms.
You need to push this rock to the other side of the hill. Brainstorm some ways that would make this easier. Write them
to the right of this picture.
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All chemical reactions need energy to start. Activation energy is the energy needed to start a reaction. Activation
energy for a chemical reaction is like the energy you would need to push a rock up a hill. Imagine if we could find
something that could make reactions happen up to 10,000,000,000 faster?! (That means a reaction that would normally
happen over 1500 years, would happen in just 5 seconds! These reaction accelerators are called enzymes. Enzymes are
special proteins called catalysts that cause reactions to happen faster.
How do enzymes work?
Enzymes lower the activation energy needed for a chemical reaction to take place. Enzymes allow the chemical reaction
to take place faster and at a lower temperature since less energy is needed. Enzymes are never used up during the
reaction, so they can do their job over and over again. Enzymes are VERY SPECIFIC and can only make a certain type of
reaction go faster. Think of how you have a key to your front door, and that key only works for your front door. Other
keys only work for other doors.
Use the following italicized information to compare
how enzymes work to a key unlocking a door
Enzymes make specific reactions go faster
ANALOGY:
Keys unlock specific doors
Enzyme Terminology
Summarize picture to left in 3 steps using the 5
terms:
Summarize picture to left in 3 steps using the 5
terms:
Notice that enzymes can catalyze a reaction in both directions. For example: Enzymes can break one substrate into two
products OR the enzyme can combine two substrates into one product.
The active site on the substrate has a unique 3-D shape that allows only a specific enzyme to bind to it. If the enzyme is
able to bind to the active site, then the chemical reaction can happen! This is called The Lock and Key Model.
Can You Stop Them?
Good question! We know what you're thinking: "What if enzymes just kept going and converted every molecule in the
world? They would never stop. They would become monsters!" There are many factors that can regulate enzyme
activity, including temperature, activators, pH levels, and inhibitors.
Controlling Enzymes
Enzymes sometimes need to be controlled. An organism can create its own molecules to slow down and stop the activity
of enzymes and proteins. At other times, enzymes can by controlled by poisons and contaminants, such as herbicides.
4 Factors that Affect Enzyme Activity
1. Temperature: Proteins (remember an enzyme is a type of protein!) change shape as temperatures change.
Because so much of an enzyme's activity is based on its shape, temperature changes can mess up the process and the
enzyme won't work. Each enzyme works best at a different temperature. High enough temperatures will cause the
enzyme to denature and have its structure start to break up.
Q: At which temperature will this enzyme work best? ________
Q: At which temperature does the reaction rate start to increase? _____
Q: At which temperature does the reaction rate start to decrease? _____
Q: At which temperature does the enzyme denature? _____
2. pH Levels: The acidity of the environment changes the shape of proteins in the same way that temperature does.
Do you remember that pH is a measure of acidity? An increased acidity near an enzyme can cause its shape to change.
Those polar and nonpolar amino acids start to twist. If there is enough of a change, the protein could unravel and
become totally ineffective.
Q: At which pH will this enzyme work best? ______
Q: At which pH does the reaction rate start to increase? _____
Q: At which pH does the reaction rate start to decrease? _____
Q: At which pH does the enzyme denature? _______
3. Inhibitors: These are the opposite of activators. Inhibitors either slow down
or stop the activity of an enzyme. They often bond to the protein, changing the
overall shape of the enzyme. Remember, when the shape changes, the enzyme will
not work the same way. A nasty example of an inhibitor is snake venom or maybe
nerve gas from World War I.
Modified from: http://www.chem4kids.com/files/bio_enzymes2.html
4. Concentration: Chemical reactions will continue to occur as long as there is enough enzymes and substrate. At
some point there will not be any more substrates for the enzymes to bind to though. This is called the point of
saturation. Think about it…..you can add as many enzymes to a solution, but once you run out of substrates, the
reaction will stop. Just like people in your house probably all have keys to your front door, but since there is only one
front door, only one key can be used at a time (even if you have 5 keys ready to use on the door!)
Practice:
Pepsin and Trypsin are enzymes found in our digestive
system that aid in digestion. Pepsin is an enzyme found in
your stomach, while Trypsin is an enzyme found in your
intestines.
What is the optimal (best) pH for Pepsin to work? _____
What is the optimal (best) pH for Trypsin to work? _____
Would the enzyme Pepsin work if it were put into your
intestines? Why or why not? ______________________
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Would the enzyme Trypsin work if it were put into your
stomach? Why or why not? ______________________
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Who cares about enzymes & reactions? How does this affect me?
Our whole body depends on chemical reactions for proper functioning. The whole digestion process allows acid to break
down our food in different parts of our body (mouth, stomach, small intestines, and then large intestines). Chemical
reactions allow different hormones to be released in our body, gives us energy and prevents build up of toxic chemicals.