The Chemistry of Life
Biochemistry –
the study of the chemical reactions that take
place in living systems
3.1: Chemical Elements and Water
 Basic unit of matter = the atom
 4 types of atoms make up 97% of all living systems:
-carbon – 19%
-nitrogen – 3%
-hydrogen – 10%
-oxygen – 65%
 atoms bond with one another to form compounds
 types of compounds = ionic or covalent
 ionic compounds: -made of metal + non-metal
-held together by ionic bond
-ionic bond = electrostatic force of attraction
formed by the gaining and losing of
electrons
 cations = atoms that lose electrons to become positively charged
 anions = atoms that gain electrons to become negatively charged
 molecular compounds:
-made of non-metal + non-metal
-held together by covalent bond
-also called covalent compounds
-covalent bond = bond formed by the
sharing of electrons between atoms
-can be single, double, or triple
-ex. F2, O2
 most biological molecules contain covalent bonds
 There are several other elements need by living organisms
SULFUR
- found in certain amino acids (the building blocks of proteins),
therefore, are required for protein and enzyme production.
- The sulfur in a.a. can lead to connections called “disulfide
bridges” which causes a protein chain to fold.
- Is a source of energy for some prokaryotes (chemo-autotrophs)
PHOSPHORUS
- a key component of ATP (chemical energy made in cellular
respiration) and DNA – both of which are found in prokaryotes,
plants, and animals
ATP – Adenosine Triphosphate
CALCIUM
- Required to form bone tissue (lack of calcium leads to
osteoporosis)
- Involved in releasing neurotransmitters for brain cell
communication
- Important in cell walls and cell membranes
IRON
- Found in the “heme” group of
hemoglobin, which is a protein in
red blood cells.
- Hemoglobin is responsible for
oxygen transport
- Oxygen binds to the iron, and is transported from the lungs to
the body cells.
- used by some bacteria to as a source of energy
- needed to form chlorophyll
SODIUM
- helps move the flagellum
- sodium-potassium pump (see cell membrane notes)
- involved in transporting glucose across the cell membrane
Polar Molecules – ex: WATER
 electrons shared in covalent bonds may be shared unequally they may spend more time around one particular atom over
another
 this is called a polar molecule = molecule in which electrons are
not shared equally thus giving one end of the molecule a partially
negative charge and the other end a partially positive charge
 electronegativity= relative ability of an atom to attract
electrons
Water (H2O)
 water is covalent but the electrons are not shared equally
 O is more electronegative than H and thus electrons spend more
time around O, making it more negative (relative to H) and H is
more positive (relative to O)
 water is therefore polar
O ∂-
H
∂+
H
∂+
 intramolecular bonds = bonds within the molecule (bonds between
the atoms that make up each individual molecule)
 intermolecular bonds = bonds between molecules
(are generally weaker than intramolecular
but cumulatively they can be quite strong)
 electrons in the intramolecular bonds of water are not shared
equally and thus water is polar
 the intermolecular bonds in water are called hydrogen bonds
 hydrogen bond (H-bond) =
forces of attraction between
a hydrogen of one molecule
and a highly electronegative
element of another molecule
(usually F, O, N)
 these H-bonds hold water
molecules together
Part F: Properties of Water
 because of water’s polarity and it’s H-bonds, it tends to posses
extraordinary properties
1) high surface tension- the H-bonds hold water molecules together,
giving it a surface like a trampoline
-ex. water strider can walk on water due to
surface tension
2) cohesive – water molecules stick together
-if you pull on one molecule it brings another with it
because of H-bonding between water molecules
-ex. transport of water up plant stems (against
gravity)
3) adhesive – water molecules stick to other substances
-its polarity allows it to attract other polar substances
-ex. drops of water on glass
4) high specific heat capacity
– water can absorb a lot of energy before its temperature
changes (heat absorbed = bonds broken)
- water can release a lot of energy before its temperature
changes (heat released = bonds formed)
-(much of E is used in the disruption or formation of Hbonds and thus E does not affect molecular motion as
quickly/dramatically)
specific heat capacity = -the amount of E required to raise the
temperature of 1 g of a substance by 1 °C
-it’s a measure of how well a substance
resists changes in temperature
-the specific heat capacity of water is 4
J/g
5) denser as a liquid than as a solid
– when water is a solid it expands since it possess a
maximum # of H-bonds which hold water molecules
further apart making it less dense
-ex. water bottle expands when frozen
-as it warms, H-bonds break and water molecules move
closer together making it more dense
-ex. ice remains on the top of frozen lakes during the
winter (liquid is below because it is more dense – allows
aquatic organisms to survive winter)
6) excellent solvent
– polar solvents dissolve in water because of it’s polarity
– acts as a medium for reactions and transport of materials
through the body.
See Figure 312 on page 35 of text