Introduction to Enzymes

The Chemical Context of Life

Objectives: Questions to be Answered:• What are enzymes?

• Why are they important?

• How do they work?

What are enyzmes?

4 Macro-moleculesof Biology

Enzymes

4 Biomolecules / Macromoleculesof Biology

Proteins Carbohydrates Lipids Nucleic Acids

Enzymes

4 Biomolecules / Macromoleculesof Biology

Proteins Carbohydrates Lipids Nucleic Acids

Enzymes

Enzymes are Proteins

• Nearly all proteins are enzymes.

• Enzymes have a specific structure that determines its specific function.

• There are 20 amino acids that make up proteins.

Why are they important?

Chemical Reactions

• Chemical reactions that release energy often occur spontaneously (on their own).

• However, chemical reactions that absorb energy will not occur without a source of energy.

• A catalyst is a substance that speeds up the rate of a chemical reaction.

• Enzymes are biological catalysts.

Biological Catalysts

• Enzymes change the rate of a chemical reaction without being used up or destroyed.

• They are essential to life in an organism because the rate of all cellular reactions is controlled by enzymes

• Enzymes are required for most chemical reactions that occur in biological organisms: Metabolism, digestion, etc.

Real-Life Example

• Hydrogen peroxide (H2O2 ) is a by-product of cellular respiration.

• It must be removed from our cells to prevent damage.

• H2O2 breaks down into water (H2O) and oxygen (O2 ) naturally, but extremely slowly.

• Catalase is an enzyme found in many cells but especially abundant in the liver.

• It is a particularly efficient enzyme, breaking down 500,000 hydrogen peroxide molecules per second.

• It drastically increases the speed of reaction.

Cirrhosis of the Liver

Reflection1. Of the four different macromolecules,

which one is almost always an enzyme?

2. What do enzymes do?

3. List one chemical reaction in living organisms that requires enzymes.

How do they work?

Activation Energy of Chemical Reactions

• For any reaction to occur, energy must be put into the reaction to start the breaking or making of new molecules.

What are the two ways to increase the rate of reaction?

1. Add energy (difficult).

2. Decrease the activation energy by adding a catalyst or an enzyme (easy).

Activation Energy

• For a reaction to occur, an energy barrier must be surmounted.

• Enzymes make the energy barrier smaller.

activation energywithout enzyme

activation energywith enzyme

energyreleased

by thereaction

products

starting substance

Active Site• A substrate is the molecule that is to be changed in

a reaction.

• The crevice in an enzyme where the substrate binds to is called the active site.

• Enzymes have a specific active site for a specific substrate and a specific reaction.

Animation: How Enzymes Work

What else do you need to

know?

Factors That Affect Enzyme Activity

• Temperature• pH

• Salt Concentration

• Temperature and pH can destroy the shape of an enzyme.

• When the shape is destroyed, so is the function. • When this happens, the enzyme is considered to

be denatured.

Keys to Remember

• Enzymes speed up chemical reactions.

• Chemical Reactions of Life require enzymes.

• Without enzymes, life processes cannot occur.

(Cellular respiration, photosynthesis, protein synthesis, digestion, etc.)

Reflection

1. What are the two ways to increase the rate of reaction?

2. What is a substrate?3. What is an active site?4. True or False. Enzymes have a specific

active site for a specific substrate and a specific reaction.

5. How might a defect in the structure of an enzyme lead to a possible health issue?