Chemistry of Life
I.
Atoms, Ions, and Molecules
A. Organisms consist of atoms of different elements
1. atoms – smallest basic unit of matter (over 1 million
atoms could fit in the period at the end of a sentence)
2. subatomic particles – there are three particles that
make up an atom
a. protons – mass of 1 amu (atomic mass unit),
positive (+) charge, in nucleus
b. neutrons – mass 1 amu, no charge (neutral), in
nucleus
c. electrons – no mass, negative charge (-), orbits the
nucleus in the electron cloud, involved in bonding
3. element – a substance of one type of atom, can not be
broken down in to simpler substances
4. 25 elements make up organisms
a. 4 elements make up 96% of the human body’s
mass (carbon, oxygen, nitrogen, and hydrogen)
b. calcium, phosphorus, potassium, sulfur, and
sodium make up most of the remaining 4%
5. Compounds – substance made up atoms of different
elements bonded together in a certain ratio
Examples: water (H2O)
glucose (C6H12O6)
B. Ions form when atoms gain or lose electrons
1. ion – atom that has gained or lost one or more
electrons
2. metals tend to lose electrons
3. nonmetals tend to gain electrons
4. ions play a role in organisms
a. hydrogen (H+) needed for production of energy for
cells
b. calcium (Ca2+) necessary for muscle movement
c. chlorine (Cl-) needed for signals in the brain
5. ionic bonds form between oppositely charged ions
C. Covalent bonds form when atoms share electrons
1. molecules – two or more elements held together by
covalent bonds
II. Properties of Water
A. Life depends on hydrogen bonds in water
1. Water is most dense at 40C, ice is less dense than liquid
water
2. Water is a polar molecule, part of the molecule is
slightly positive and part is slightly negative
3. Oxygen and hydrogen do not share electrons equally,
oxygen has the electrons more than hydrogen
4. Hydrogen bonds are when the slightly positive part of
one water molecule bond with the slightly negative
part of another water molecule
5. Properties Related to Hydrogen Bonding
a. high specific heat
b. Cohesion
c. Adhesion
B. Many compounds dissolve in water
1. solutions are homogeneous mixtures
2. solvent is the substance that does the dissolving
3. solute is the substance being dissolved
4. like dissolves like (polar solvents dissolve polar solutes
and nonpolar solvents dissolve nonpolar solutes)
C. Some compounds form acids and bases
1. Acid – compound that releases protons (hydrogen
ions) when it dissolves in water
2. Base – compound that produces hydroxide ions OH3. Acidity or hydrogen ion concentration is measured on
a pH scale.
0 1 2 3 4 5 6
more acidic
high H+
concentration
7
8 9 10 11 12 13 14
neutral
more basic 
low H+
concentration
4. Buffer – a compound that does not let pH of a solution
change suddenly
III. Carbon- Based Molecules
A. Carbon atoms have unique properties
1. Each carbon atom has 4 valence electrons available for
bonding
2. Each carbon atom can bond with 4 other atoms
3. Carbon-based molecules have three fundamental
structures
a. straight chains
b. branched chains
c. rings
4. monomer – subunit of a complete molecule
5. polymer – large molecule of many monomers linked
together
B. Four types of carbon-based molecules are found in living
things
1. Carbohydrates – starches and sugars
a. monosaccharide – simple sugars (fructose and
glucose)
b. disaccharide – two sugars bonded together
c. polysaccharide – polymers of monosaccharide
(starch and cellulose)
2. Lipids – nonpolar molecules that include fats, oils, and
cholesterol
a. fats store large amounts of chemical energy in
organisms
b. saturated fats have a maximum number of bonds
with hydrogen atoms
c. unsaturated fats have less than the maximum
number of bonds with hydrogen
3. Proteins – a polymer made up of monomers called
amino acids
a. there are 20 different amino acids to build proteins
b. your body can make 12 amino acids, the other 8
must come from the food we eat
c. amino acids have a carbon atom bonded to 1) a
hydrogen atom, 2) an amino group, NH2, 3) a
carboxyl group and 4) a side group that makes
them unique
d. polypeptide bonds bind amino acids together
4. Nucleic acids – polymers made up of monomers called
nucleotides
a. a nucleotide is made up of a sugar, phosphate
group, and nitrogen containing base
b. nucleic acids make up DNA and RNA, they are the
instructions for making proteins
IV. Chemical Reactions – substances change into different
substances
A. 6O2 + C6H12O6  6CO2 + 6H2O
 means yields
Reactants
Products
B. Bond Energy – amount of energy that will break a bond
between two atoms
C. Equilibrium – when both reactants and products are made
at the same rate
D. Activation Energy – the amount of energy that needs to be
absorbed for a chemical reaction to start
E. Exothermic reaction – reaction that releases more energy
than it absorbs
F. Endothermic reaction – reaction that absorbs more energy
than it releases
V.
Enzymes
A. Catalyst – a substance that decreases the activation energy
needed to start a chemical reaction
B. Enzymes – catalyst for chemical reactions in living things
C. Substrate – the specific reactant that an enzyme acts on
D. Lock-and-key model – enzymes must fit on to the substrate
The End