2-4 Chemical Reactions and Enzymes

I. Chemical Reactions

A. A chemical reaction is a process that changes one set of chemicals into another by changing the chemical bonds in compounds.

B. Mass and energy are NOT created or destroyed in a chemical reaction

C. Compounds on the left side are reactants

D. Compounds on the right side are products.

Example:

6CO2 + 6H2O C6H12O6 + 6O2

Reactants Products

The same amount of each element is found on both sides of the arrow…Not created or destroyed!

E. Important chemical reaction in the bloodstream

1. Carbon dioxide entering your blood reacts with water to produce carbonic acid (H2CO3) that is soluble in blood

2. In the lungs, the reaction is reversed and you exhale the carbon dioxide

gas.

3. carbonic anhydrase speeds it up by 10 million times so you don’t die!

Exergonic – Chemical reactions thatrelease energy when bonds are broken

Example: the body breaks down large food molecules to release

the energy in the bonds (metabolism)

Endergonic – Chemical reactions that store energy by creating bonds (need help to start)

Example: the body stores excess energy in molecules to be used later.

IV. Activation Energy

A. Sometimes reactions

need a push to get

started (activation energy)

B. Cellulose in plants is used to make film and paper…VERY flammable

C. Does not spontaneously burst into flames unless energy is there to start it (flame).

D. Activation energy is the energy required to get the reaction started

E. Endothermic: products have more energy than reactants (energy absorbing)

F. Reverse is true for exothermic (energy releasing)

V. EnzymesA. Enzymes are proteins

B. Enzymes are necessary for the chemical reactions that occur in living cells.

C. Enzymes are not changed by the reaction. They are used again and again.

D. Some chemical reactions are too slow and Catalysts are needed to speed up the reaction

E. Enzymes are catalysts. They give the reaction the boost it needs to get started faster.

F. Enzymes are specific – bring certain reactants (substrate) together to react faster.

G. Each only work on one kind of reaction

H. Lactose sugar needs Lactase enzyme to break it down faster in the

digestive system.

I. Enzyme fits with substrate like a lock and a key.

J. Enzymes’ ability to act depends on their shape.

K. On the surface of each enzyme there is a region called the active site.

L. When the substrate molecule comes in contact with the active site, it

forms an Enzyme-Substrate complex.

VI. Factors affecting enzymesA. Temperature

1. Low temperatures slow down the formation rate for enzyme-substrate complexes. The effect of the enzyme is reduced.

2. High temperatures cause the enzyme to break down. This process is called denaturation.

3. The perfect temperature is usually close to the normal cell temperature. (37oC or 98.6oF in humans)

B. pH

1. Every enzyme works best at a certain pH.

Example:

Pepsin breaks down protein in the stomach, it works best in an acidic environment.