The Chemistry of Life
Concepts taken from chapters 2, 3 & 4
Biology – Kevin Dees
• Organisms are composed of matter
• Anything that takes up space and has mass
• Abiotic items are also composed of matter
• Matter is made up of elements
• A substance that cannot be broken down into other
substances by chemical reactions
• There are about 92 naturally occurring elements
–
–
–
–
–
Biology – Kevin Dees
Oxygen, O
Carbon, C
Iron, Fe
Zinc, Zn
Etc…
Of the 92, naturally occurring elements,
only 25 are known to be essential to life
• of these 25, only four (4) compose approx.
96% of living matter
– Carbon, C
– Oxygen, O
– Hydrogen, H
– Nitrogen, N
Biology – Kevin Dees
Trace elements
• Required by organisms in very small
quantities
• Still very important despite their limited
abundance
– Fe, iron – required for oxygen transport
– I, iodine – needed to produce a hormone in
the thyroid gland - goiter
Biology – Kevin Dees
Atoms
• The properties of elements depend on
atoms
• Smallest unit of matter that retains the properties
of an element
• Atoms are composed of subatomic
particles
• Neutrons- no charge “neutral’
• Electrons – negative charge
• Proton – positive charge
Biology – Kevin Dees
Structure of atoms
• Nucleus
– Protons
– Neutrons
• Electrons orbit
the nucleus
Biology – Kevin Dees
Atoms join to form molecules and compounds
• Two or more atoms join to form a molecule
– i.e. H2 - hydrogen molecule
• A compound consists of two or more
different atoms joining to form a molecule
– i.e. H2 O – water molecule; also a compound
Biology – Kevin Dees
Chemical bonds hold atoms together in
molecules and compounds
• Covalent bonds
– Sharing of electrons by atoms
– Very strong
– Represented by dashed line in structural
formula
• H-O-H
– May be single (one pair of electrons shared )
or double (2 pr. shared)
– May create polar molecules ( areas of charge)
• H2O is polar
Biology – Kevin Dees
Water molecule – example of polar covalent
bonding
Biology – Kevin Dees
• Ionic bonding – transfer (loss or gain) electrons
– Formation of ions – charged atom
• Cation – positive charge – lost electron
• Anion – negative charge – gained electron
– Bonds form due to attraction between anions
and cations
– Very strong
Biology – Kevin Dees
• Hydrogen bonds
– Very weak individually;
strength in numbers
– Attractions between
partially positive H atoms
and partially negative
atoms
– Example: joins water
molecules together
Biology – Kevin Dees
Fig. 2-UN2
2 H2
Reactants
Biology – Kevin Dees
2 H2O
O2
Reaction
Products
Water – special properties
•
Hydrogen bonding and polarity make
water very important to life’s processes
• Water is :
Cohesive – hydrogen bonding holds
water molecules together
Adhesive – clings to other things
Biology – Kevin Dees
Water molecules pulled up the tissues of a plant
or
creates surface tension on water’s surface
Biology – Kevin Dees
• Water is :
–Able to absorb large quantities of
heat and only slightly change its
own temperature – specific heat
• Affect on climate – moderates coastal
climates
• Insulation
• Evaporative cooling – as water
absorbs energy and changes state
(from liquid to gas), heat energy is
taken away
Biology – Kevin Dees
• Water is:
– Less dense as a solid than a liquid
– “Ice floats”!!!!
– This is important to water bodies
as they freeze in the winter. The
ice floats and insulates the water
beneath it!!!
Ice –stable crystals due to
H bonds
Biology – Kevin Dees
Liquid water – H bonds
break and reform
• Water is:
– The universal solvent
– The mixing of two or more substances is
known as a solution
• The dissolving agent is the solvent
• The substance dissolved is the solute
– Water dissolves polar or ionic compounds
» Hydrophilic - water loving
– Water does not dissolve nonpolar compounds
» Hydrophobic - water hating
Biology – Kevin Dees
Water molecules may also
dissociate – form ions
• H2O  H+ + OH• water  hydrogen ion + hydroxide ion
H+ > OH- = Acidic
Biology – Kevin Dees
Neutral
• These ions effect the pH (concentration of Hydrogen
ions)
• pH scale:
• Buffers - minimize change in hydrogen and hydroxide
7
ions 0
14
H+ < OH- = Basic
The importance of carbon
Water is the universal medium for life but all life is made of chemical
compounds that contain carbon
• Organic compounds
– Compounds that contain covalently bonded carbon
– Inorganic compounds - non-organic (NaCl)
– Hydrocarbons – organic molecules with only carbon
and hydrogen
– Lots of stored energy!!!!!!
– ATP (adenosine triphosphate) – energy currency of
the cell
Biology – Kevin Dees
Properties of organic molecules depend on the
arrangement of the carbon skeleton and the
molecular attachments to that carbon skeleton
• Carbon skeleton
• Functional groups
• Properties – determine
function
Biology – Kevin Dees