From molecules to
cells
© 2007 Paul Billiet ODWS
The levels of organisation in cells
THE CELL
Organelles
Supramolecular
assemeblies
CHLOROPLASTS, MITOCHONDRIA, NUCLEUS etc
ENZYME COMPLEXES, RIBOSOMES, CHROMOSOMES
Macromolecules
NUCLEIC
ACID
PROTEIN
POLYSACCHARIDE
LIPID
Building blocks
NUCLEOTIDE
AMINO
ACID
SIMPLE SUGAR
FATTY
ACID &
GLYCEROL
Precursors from
the environment
CO2, H2O, MINERALS
© 2007 Paul Billiet ODWS
Elements in living & non-living
material
© 2007 Paul Billiet ODWS
EARTH’S CRUST
RANK
ELEMENT
HUMAN TISSUES
%
ELEMENT
%
1st
O
62,5000 H
60,300
2nd
Si
21,2000 O
25,500
3rd
Al
6,4700 C
10,500
4th
Na
2,6400 N
2,450
5th
Ca
1,9400 Na
0,730
6th
Fe
1,9200 Ca
0,266
7th
Mg
1,8400 P
0,134
8th
P
1,4200 S
0,132
9th
C
0,0800 K
0,036
10th
N
0,0001 Cl
0,032
Elements in living & non-living
material
EARTH’S CRUST
RANK
ELEMENT
1st
Oxygen
2nd
HUMAN TISSUES
%
ELEMENT
%
62,5000
Hydrogen
60,300
Silicon
21,2000
Oxygen
25,500
3rd
Aluminium
6,4700
Carbon
10,500
4th
Sodium
2,6400
Nitrogen
2,450
5th
Calcium
1,9400
Sodium
0,730
6th
Iron
1,9200
Calcium
0,266
7th
Magnesium
1,8400
Phosphorus
0,134
8th
Phosporus
1,4200
Sulphur
0,132
9th
Carbon
0,0800
Potassium
0,036
10th
Nitrogen
0,0001
Chlorine
0,032
Water


Formula
H2O
Structure
Slightly () negative at the oxygen
end and slightly positive at the
hydrogen end
-
O
H
+
© 2007 Paul Billiet ODWS
H
+
The association between the
polar water molecules
Weak
hydrogen
bonds
© 2007 Paul Billiet ODWS
Comparing molecules
Molecule
Formula Molecular
mass
Melting
point
/ °C
Boiling
point
/ °C
Methane
CH4
16
-184
-161
Ammonia
NH3
17
-78
-33
Water
H2 O
18
0
+100
Hydrogen
fluoride
Hydrogen
sulphide
HF
20
-92
+19
H2 S
34
-86
-61
Compared to molecules of similar size and properties
water has a very high melting point and boiling point
© 2007 Paul Billiet ODWS
Thermal properties
The molecules of water can absorb a lot of
heat energy
 Water has a very high thermal capacity
(4.2 J°C-1 g-1)
 The hydrogen bonding forms a lattice
which does not easily fall apart as the
temperature rises

© 2007 Paul Billiet ODWS
Thermal properties and life
Water is a very, thermally stable medium
 Water helps living organisms resist
changes in their environment
 To make water change from a liquid to a
vapour requires a lot of energy
 Evaporation of water on a the surface of a
body cools it down significantly

© 2007 Paul Billiet ODWS
African elephants (Loxodonta africana) bathing
© Shirley Burchill 2007
© 2007 Paul Billiet ODWS
Solvent properties





The polar properties of water make it a good
solvent for:
Polar molecules (e.g. sugars and alcohols)
These form hydrogen bonds with the water
molecules
Ionic compounds (e.g. salts, acids and bases)
These dissociate into their component ions
© 2007 Paul Billiet ODWS
Solvent properties and life
Water is a very important transport
medium for living organisms
 because of its solvent properties and
 because it remains a liquid over a large
range of temperatures
 Water is also an important medium for
biochemical reactions

© 2007 Paul Billiet ODWS
Webvision
Cohesion




The cohesion (stickiness) between water
molecules
Water molecules are also attracted to wettable
surfaces
Very tall thin columns of water can be supported
before they break
The tallest are at the physical limits of water
trees (sequoia and eucalyptus are 100m tall)
© 2007 Paul Billiet ODWS
Giant red wood
Sequoiadendron
giganteum
California USA
Eucalyptus
grandis
Public Domain image
NSW
Australia
Public Domain image
Surface tension


Water molecules hold together forming a skin at
the surface
This is strong enough for some organisms to be
supported
Water skater
Gerris gibbifer
© 2007 Paul Billiet ODWS
Water Skater © Shirley Burchill
2007
Density





Water is densest at 4°C whilst it is still a liquid
So ice floats on the surface of water
Organisms which
live in water do not
risk freezing solid
so easily
Freezing is usually
fatal
Water forms a
good habitat for
living organisms
© 2007 Paul Billiet ODWS
Iceberg, Antarctica © Shirley Burchill 2007
Transparency




Water is a transparent liquid, light passes though it
Blue light, with the most energy, penetrates furthest, red
light is the weakest and penetrates least
Plants can photosynthesise under water
Animals can use their visual systems
Kelp forests (Macrocystis pyrifera)
California
© Mike Graham, Phycology Lab @ Moss Landing Marine
Laboratories
© Text 2007 Paul Billiet ODWS