1. Enzymes and Chemical Reactions
5.3,
Edited by C. Kerins

2. Introduction to Chemical Reactions
Chemical reactions convert one set of substances into a completely different set of substances that have very different physical and chemical properties than those of the beginning substances.
C6H12O6+6O2ATP + 6H2O + 6CO2
Glucose Oxygen energy water carbon dioxide

3. Reactants and Products
C6H12O6+6O2ATP + 6H2O + 6CO2
Glucose Oxygen energy water carbon dioxide
Reactants: the substances that go INTO a chemical reaction
Products: the substances that are PRODUCED in a chemical reaction
Remember, chemical reactions do NOT change the numbers and kinds of atoms…they just break old bonds and form new ones to make the new substances.

4. Exergonic and Endergonic Reactions
Chemical reactions can either absorb energy from or release energy into the environment.
Chemical reactions that release energy often occur spontaneously. These are endergonic reactions.
Chemical reactions that absorb energy will not occur without a source of energy. These are called exergonic reactions.
Energy of activation (activation energy): Amount of energy that must be put in before an exergonic reaction will proceed (the energy barrier)

6. 5.5 HOW ENZYMES FUNCTION
Enzymes are proteins that speed up the cell's chemical reactions by lowering energy barriers.
Enzymes lower the activation energy needed to get a chemical reaction started.
They are used in both exergonic and endergonic reactions.

8. Enzymes: proteins that function as biological catalysts
Catalyst: any substance that speeds up the rate of a chemical reaction
Enzymes increase the rate of a reaction by decreasing the activation energy necessary to begin the reaction.
Enzymes remain UNCHANGED following reactions they catalyze.

9. Enzyme-Catalyzed Reaction
EA without
enzyme
EA with
enzyme
Reactants
Energy
Net
change
in energy
Products
Progress of the reaction

10. 5.6: Enzyme Catalyzed Reactions
Each enzyme catalyzes only ONE chemical reaction.
There are thousands of chemical reactions that occur in organisms, therefore there are thousands of different enzymes.
Enzymes are VERY specific!!!!

11. Each enzyme has a unique three-dimensional shape that determines which chemical reaction it catalyzes
Substrate: a specific reactant that an enzyme acts on
Active site: A pocket on the enzyme surface that the substrate fits into—only fits its SPECIFIC substrate!!!!

12. Induced fit: The way the active site changes shape to "embrace" the substrate
A single enzyme may act on thousands or millions of substrate molecules per second
REMEMBER: Enzymes are protein molecules that function as biological catalysts, increasing the rate of chemical reactions without being changed into different molecules or being consumed.

13. LE 5-6 Enzyme available with empty active site Active site Substrate
(sucrose)
Substrate binds
to enzyme with
induced fit
Enzyme
(sucrase)
Glucose
Fructose
H2O
Products are
released
Substrate is
converted to
products

14. 5.7: The cellular environment affects enzyme activity
Physical factors influence enzyme activity and maximize an an enzyme’s effectiveness
Temperature (for humans optimal is C)
salt concentration
if an environment is too salty, salt ions interfere with some of the chemical bonds that maintain protein structure
pH (for most enzymes, optimal is 6-8)
This is why maintaining homeostasis is so important!

15. Some enzymes require nonprotein helpers called cofactors
Inorganic cofactors include metal ions, like zinc, iron, and copper
Organic cofactors are called coenzymes
Normally vitamins or made from vitamins
Vitamin B6 is used to convert one amino acid to another

16. 5.8 Enzyme inhibitors block enzyme action
Inhibitors interfere with an enzyme's activity
A competitive inhibitor takes the place of a substrate in the active site
A noncompetitive inhibitor alters an enzyme's function by changing its shape
In feedback inhibition, enzyme activity is blocked by a product of the reaction catalyzed by the enzyme

17. Normal binding of substrate
LE 5-8
Substrate
Active site
Enzyme
Normal binding of substrate
Competitive
inhibitor
Noncompetitive
inhibitor
Enzyme inhibition