Biology
Name: _____________________________________________ Date: _________________
Handout
2-5
Block: _______
Objective: IWBAT summarize how enzymes participate in chemical reactions.
CW: Questions
1. In your own words, define chemical reaction.
2. In your own words, define activation energy.
3. In your own words, define enzyme.
For #4-7, use the following graph:
4. Outline in the graph where you find the reactants
5. Outline in the graph where you find the products
6. Outline in the graph where you find the activation energy without using an enzyme
7. Outline in the graph where you find the activation energy with using an enzyme
8. Come up with a real world analogy for activation energy and write it below (an example is the energy it takes to push a
rock up a hill, so that it can fall down the other side quickly):
9. What effect does an enzyme have on the speed of a chemical reaction? What effect does an enzyme have on the
activation energy?
10. Make an analogy for how an enzyme works:
11. How are enzymes similar to a lock-and-key?
12. Describe what is happening in each of the three pictures shown to the right.
Be sure to use the words: substrate(reactant), active site, enzyme, and products.
Homework: ON SEPARATE PAPER, define the terms below, give an example of each, and draw a picture of each term
or paste a magazine clip. (1) Chemical reaction, (2) Substrates/reactants, (3) Products, (4) Activation Energy, (5)
Enzyme, (6) Active site, (7) Lock-and-key EXTRA (8) Protein shape.
Enzymes
What are Enzymes?
Each time a cell repairs DNA, breaks down sugar molecules to release energy, or builds proteins, a chemical reaction
occurs. Chemical reactions can build, break down, or transform molecules. The molecule(s) involved in the reaction are
known as the substrates or reactants. The molecule(s) produced during a reaction are known as the products. In the
following reaction, lactose is the substrate and the glucose and galactose molecules are the products.
In that reaction, lactase is the enzyme. Enzymes are proteins made by cells that act as catalysts in biochemical reactions.
Enzymes speed up chemical reactions by reducing the required activation energy, which is the amount of energy needed
to start the reaction. The following graph shows this:
How do Enzymes Work?
Enzymes are proteins. All proteins have a specific shape based on their sequence of amino acids. Part of the enzyme’s
shape is an active site. The substrates bind to this active site, reducing the activation energy, and allowing the chemical
reaction to occur. The lock-and-key model illustrates this idea. Just as a key fits into a lock, a substrate fits into an enzyme.
Because of this, each enzyme can only deal with one specific substrate and cause one specific chemical reaction. The
active site fits one substrate.
After the reaction, the substrates are released from the enzyme. The enzyme remains intact after the reaction is complete
and can continue to catalyze the same reaction.