THE CHEMISTRY OF LIFE
Chapter 2
A. Matter - takes up space.
1. Elements
Pure chemical substances composed
of atoms.
✦ Examples?
✦ 109 elements named thus far
Periodic Table of Elements
2. Atom
Composed of 3 subatomic particles:
✦ Protons
✦ Neutrons
✦ Electrons
Characteristics of Subatomic Particles
Atomic number
# protons in nucleus of an atom
(establishes identity of the atom)
Since most atoms are electrically
neutral, atomic number indicates #
of electrons as well.
Atomic mass
# protons plus # neutrons in nucleus
of an atom
How can we determine the number of
neutrons in an atom?
# neutrons = atomic mass - atomic #
✽ Determine # neutrons in a carbon
atom (atomic mass = 12; atomic # = 6).
# neutrons = 12 - 6 = 6
Do all carbon atoms have the same
number of protons?
Do all carbon atoms have the same
number of neutrons?
Isotopes
Atoms having the same number of
protons, but differing numbers of
neutrons.
Ex. Carbon isotopes
✦ carbon 12 (12C) → 6 neutrons
✦ carbon 13 (13C) → 7 neutrons
✦ carbon 14 (14C) → 8 neutrons
Periodic table information on carbon:
Atomic mass given in table is average
mass of all the element’s isotopes.
5. Chemical Bonds
Type of bond formed is determined
by the number of valence electrons
in the interacting atoms [octet rule].
a) Covalent bonds - atoms share
electron pairs.
✦ strongest type of bond
✦ tend to form when atoms have 3, 4
or 5 valence electrons
✦ can be nonpolar or polar
Nonpolar covalent bonds - electrons are
shared equally between atoms.
Ex. methane
Polar covalent bonds - electrons are
drawn more strongly to 1 atom’s nucleus
than the other.
Form when less electronegative atoms
bond with more highly electronegative
atoms.
Ex. water
b) Ionic bonds - form when oppositely
charged ions are attracted to each other.
✦ weaker than covalent bonds
✦ atoms with 1, 2 or 3 valence electrons
give up electrons to atoms with 7, 6 or
5 valence electrons
✦ form salts
Ex. NaCl
c) Hydrogen bonds - form when opposite
charges on two molecules are
attracted to each other.
✦ weakest type of bond*
Ex. DNA H 2O
3. Acids & Bases
✽ Acids - add H+ to a
solution.
✽ Bases - remove H+
from solution.
pH scale is measure
of acidity/alkalinity
based on H+
concentration.
C. Major Organic Molecules
Molecules that contain carbon in
combination with hydrogen.
1. Carbohydrates
✦ contain C, H & O [# C ≅ # O]
✦ function to store energy & provide
support
✦ building blocks (monomers) are
monosaccharides
Monosaccharides
✦ simple sugars containing 3 - 7 carbons.
✦ C, H, O ratio is 1:2:1
Disaccharides
✦ simple
sugars composed of 2
monosaccharides linked together by
dehydration synthesis.
Other common disaccharides: maltose
(seed sugar) & lactose (milk sugar).
Polysaccharides
✦ complexcarbohydrates made up of
hundreds of monomers linked by
dehydration synthesis.
2. Lipids
✦ contain C, H, O [# C >> # O]
✦ do not dissolve in water
Triglycerides (fats)
✦ composed of glycerol linked to 3
fatty acid chains
✦ function to cushion organs, as
insulation & in long-term energy
storage (adipose tissue).
Phospholipids
✦ lipid
bonded to a phosphate group
✦ major component of cell membranes
Sterols
✦ lipids
that have 4 interconnected
carbon rings
Ex. Vitamin D, cortisone, estrogen &
cholesterol
Waxes
✦ fatty acids combined with hydrocarbons
✦ help waterproof fur, feathers, leaves &
fruits
3. Proteins
✦ contain
C, H, O, N, (S)
✦ monomers are amino acids
Proteins have a 3-dimensional shape
(conformation):
✽ primary (1o) structure - amino acid
sequence of polypeptide chain
✽ secondary (2o) structure - coiling &
folding produced by hydrogen bonds
✽ tertiary (3o) structure - shape created
by interactions between R groups
✽ quarternary (4o) structure - shape
created by interactions between two or
more polypeptides
Examples:
✦ antibodies
✦ hemoglobin
✦ insulin & glucagon
✦ keratin
✦ fibrin & thrombin
✦ spider silk (strongest natural fiber known)
✦ enzymes (maltase, pepsin, lipase)
4. Nucleic Acids
✦ contain
C, H, O, N, P
✦ monomers are nucleotides
DNA (deoxyribonucleic
acid)
✦ 5-carbon sugar is
deoxyribose
✦ nitrogenous bases
are A, G, C & T
✦ double-stranded
helix held together
by hydrogen bonds
✦ is the genetic
material
RNA (ribonucleic acid)
✦ 5-carbon sugar is
ribose
✦ nitrogenous bases
are A, G, C & U
✦ single-stranded
✦ enables information
in DNA to be
expressed
