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Chemistry of Life
Topic 3
The most frequently occurring chemical
elements in living things are Carbon,
Hydrogen, Oxygen and Nitrogen
- found in all carbohydrates,
proteins, lipids,
and nucleic acids
A variety of other elements are needed
by living organisms but are less common,
including:
·Sulfur
·Calcium
·Phosphorus
·Iron
·Sodium
·Potassium
Element
Example role in
plants
Example role in
animals
Example role in
prokaryotes
Sulfur
in some amino
acids
in some amino
acids
in some amino acids
Calcium
co-factor in some
enzymes
co-factor in some
enzymes &
component of
bones
co-factor in some
enzymes
Phosphorous
phosphate groups
in ATP
phosphate groups
in ATP
phosphate groups in
ATP
Iron
in cytochromes
in cytochromes &
haemoglobin
in cytochromes
Sodium
in membrane
function
in membrane
function & sending
nerve impulses
in membrane
function
H2 O
POLARITY – POLAR BEAR!!!
Structure of water
·The H - O bond in water is a polar covalent bond.
·The nuclei of oxygen is significantly larger and has a greater charge
than the nuclei of hydrogen
·Consequently the electron pair in the covalent bond is found ‘closer’
to the oxygen than the hydrogen nuclei
·This creates a polar molecule in which oxygen carries a small
negative dipole and hydrogen carries a small positive dipole
Hydrogen Bond Formation
·Because of the partial charges, Oxygen
atoms of each molecule are attracted to the
hydrogen atoms of other molecules
·H-bonds are key to many of water's
properties
·H-bonds are essential for many biological
molecules to form, nucleic acids being the
most important
H
O
H
O
H
H
O
H
H
Properties of Water
Cohesive: water molecules tend to attract each
other and stick together
·
Causes water to have a high surface tension
- forms droplets
- vascular tissue in plants can draw
water up to great heights against gravity
- helpful to organisms such as water bugs
who walk on water
·Causes many of water's thermal properties
Thermal: water has a high specific heat capacity (or simply
specific heat)
·Heat capacity is defined by the amount of energy needed cause a
rise in temperature
·Water can absorb or release a lot of heat before changing
temperature
·It takes energy to break the H bonds and get water molecules to
increase in kinetic energy
·e.g. the water in blood keeps your body temperature fairly stable
This is also why water provides such a great
living environment for many organisms
• Ocean temperatures only fluctuate by +/1.5 degrees throughout the year.

Coolant
·Heat generated by the metabolic process of the
body must be removed in order to prevent
enzyme denaturation
·Water in the blood helps to carry this heat to your
skin where it can be transferred to the air
·Sweat also helps to carry heat away from your
body
Water also has a high heat of vaporization
·Because it takes a lot of energy (heat) to get water
to change state, evaporating water takes a lot of
heat with it.
·e.g. sweating: heat from the body causes sweat to
evaporate, which removes heat and cools the body.
Ecological effects
·high specific heat capacity of water allows it to
maintain stable temperatures, excellent living
environment for many organisms
·moderates the environmental temperature
Solvent: The polarity of water gives it strong
solvent properties for polar or ionic solutes
·Majority of molecules found in and around
cells are polar or ionic: carbohydrates, protein,
nucleic acids (DNA, RNA)
·"Like dissolves like"
·The polar water molecules are attracted to the
charges in the solute (e.g. sodium)
Transport Medium
·Blood is mostly water
- Transports blood cells and dissolved molecules
-Common solutes in blood: glucose (blood sugar)
amino acids, fibrinogen (protein for blood clotting),
hydrogencarbonate ions (a means of transporting
CO2)
·
Vascular tissue in plants
- Xylem carries water and dissolved minerals up
from roots
- Phloem carries dissolved sugars down from
leaves
Metabolic Medium
·Being a good solvent for biochemicals means water is also a
good medium for biochemical reactions
Aqueous
Solution
Location
Common Reactions
cytoplasm
fluid inside cell but outside
organelles
glycolysis / protein synthesis
reactions
nucleoplasm
fluid inside nuclear
membrane
DNA replication / transcription
stroma
fluid inside chloroplast
membrane
light-independent reactions of
photosynthesis
blood plasma
fluid in arteries, veins and
capillaries
loading and unloading of
respiratory gases / clotting