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