• All the chemical reactions in our
bodies are called metabolism.
•Breakdown and reassemble
molecules in the body.
• Chemical bonds are broken and
formed during chemical
reactions.
REACTANTS
YIELDS
CH4 + 2O2 
(methane) + (oxygen)

PRODUCTS
CO2 + 2H2O
(carbon dioxide) + (water)
• Coefficients = # of molecules of a
compound
 Ex: 6O2 = 6 molecules of Oxygen (O)
 3H2O = 3 molecules of H2O
CH4 + 2O2 
CO2 + 2H2O
• Subscripts = # of atoms of an element
 Ex: CH4 = 1 atom C, 4 atoms H
 CO2 = 1 atom of C, 2 atoms O
CH4 + 2O2 
CO2 + 2H2O
• How many atoms of O are in 6O2 ?
12 atoms of O!
• In ALL chemical equations the same
number of atoms of elements are on the
reactant and the product side of
chemical equations
o Why?
 Because of the Law of Conservation
of Matter (atoms are never created
or destroyed; they are simply
rearranged!)
oWe balance equations so the Law of
Conservation of Mater is NOT
violated!
oWe must always balance equations
using coefficients!!
oSubscripts can never be changed!
oCoefficients must always be placed
in FRONT of the entire compound!
oCreate an atom inventory
H2 +
O2 
H2O
CaO + KBr  K2O
+ CaBr2
Al2S3 + BaCl2  AlCl3 + BaS
• The key to a
chemical reaction is
energy!
• Most compounds in
living things cannot
undergo chemical
reactions without
energy
• Activation energy = the
minimum amount of energy
needed for reactants to
form products in a
chemical reaction
o Look at Graph A: the
peak in the graph
represents the amount
of energy that must be
added to the system to
make the reaction occur!
Graph A
• All living things are chemical factories driven
by chemical reactions!
• Enzymes (catalysts) need to be present in
order to reduce the activation energy and
allow the reaction to proceed quickly.
• Look at Graph B: the enzyme lowers the
activation energy and the product will
be formed sooner!
Graph B
• Catalyst = a substance that lowers
the activation energy needed to start
a chemical reaction.
• Enzyme = special proteins that are
biological catalysts that speed up the
rate of a chemical reaction
Essential to life!
Specific to one reaction
How do ENZYMES Work?
• The reactants that bind to the
enzyme are called substrates.
• The specific location where a
substrate binds on an enzyme is
called the active site.
How do ENZYMES Work?
• The active site and substrate have
complementary shapes (lock-andkey).
oEnzymes are very specific for the
substrates that will change!
How do ENZYMES Work?
• When the enzyme-substrate complex
forms, chemical bonds are broken and
new bonds form to produce the
products.
• Enzyme releases the product and the
enzyme can be used again
Factors That Affect Enzymes:
1) pH (how acidic or basic a
substance is)
2) Temperature
• most enzymes in human cells
are most active at 98.6F
• pH & temperature will denature (change
the shape) of the enzyme so it will not be
able to bond with the corresponding
substrate!
Examples Of Enzymes Working:
• Helps with digestion
• DNA replication
• Enzymes in the venom of a
venomous snake break down the
membranes of a person’s red blood
cells
Examples Of Enzymes Working:
• Hard green apples ripen because of
the action of enzymes
• Photosynthesis and cellular
respiration provide energy for the
cell with the help of enzymes
• pH = how acidic or basic a
substance is
• Acid = substance that forms H+
(hydrogen ions) in water
Water
HCl  H+ + Cl- (pH LESS than 7)
• Base = substance that forms OH(hydroxide ions) in water
Water
NaOH  Na+ + OH(pH MORE than 7)
0
7
ACID
N
E
U
T
R
A
L
14
BASE