Chemical Reactions• Chemical reactions = the breaking and creating

of bonds between different substances (this

requires energy)

• Activation energy = The amount of energy

needed to make a chemical reaction start

Chemical Reactions• Reactants (substrate): substances that are

changed during a reaction

• Products: substances that are made by a

chemical reaction

reactants products

Types of Reactions• Overall, reactions absorb or release energy.

• Endothermic: absorbs energy

• Ex. Photosynthesis

• Exothermic: releases energy

• Ex. Cellular Respiration

EXOTHERMICENDOTHERMIC

Less energy

in products

than reactants

More energy

in products

than reactants

6CO2 + 6H2O C6H12O6 + 6O2

Photosynthesis

Energy is stored as sugar, therefore it is an

ENDOTHERMIC reaction

C6H12O6 + 6O2 6CO2 + 6H2O

Cellular Respiration

Energy is released as ATP when sugar is broken

down, therefore it is an EXOTHERMIC reaction

Key Biochemical Reactions

• Enzymes are a type of PROTEIN that speed up biochemical reactions by lowering the activation energy.

– Because they speed up reactions, they are called catalysts.

• Enzymes are specialized molecules that bind to reactants (aka, substrate) and help to break or form bonds. Then they release a newly created product.

• Enzymes are not changed in a reaction and can be used over and over again!

Enzymes

• Enzymes are very specific– They have an active site that fits only

one substrate (reactant)

– This is known as the lock and key model

Enzymes

enzyme

active site

substrate

(reactant)

Enzymes

• Enzymes can break bonds in substrate to form two products

Substrate

enzyme

(Bonds breaking)

Products

Enzymes• Enzymes can make bonds between substrates to

form one product

enzyme

Substrates

(Bonds forming)

Product

Denaturation• Enzyme’s active site gets deformed and

loses its specific shape causes a loss of biological activity– Caused by: extreme changes in pH,

temperature, ion strength, and solubility

• Enzymes can be “renatured” to their original shape but not always

Normal enzyme Denatured enzyme

1. Temperature = increasing temperature

increases the rate of the reaction

– Molecules are moving FASTER due to an

increase in kinetic energy, so they collide more

with each other

2. pH = how acidic a solution is

– Most enzymes only work at very specific pH so if

the pH changes it can affect speed of reaction

Ways to change the rate of a chemical reaction

3. Substrate Concentration = the higher the amount of substrate, the faster the reaction– Due to more particle collisions

4. Catalysts = (like enzymes) speed up reactions – Lower activation energy needed for the reaction to

start

5. Competitive Inhibitor = slows down reaction

– Competes with substrate for the active site on the enzyme

Ways to change the rate of a chemical reaction