From molecules to cells © 2007 Paul Billiet ODWSODWS

From molecules to cells

© 2007 Paul Billiet ODWS

THE CELL

Organelles CHLOROPLASTS, MITOCHONDRIA, NUCLEUS etc

Supramolecular assemeblies

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

The levels of organisation in cells


Elements in living & non-living material

EARTH’S CRUST HUMAN TISSUES

RANK ELEMENT % 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 HUMAN TISSUES

RANK ELEMENT % ELEMENT %

1st Oxygen 62,5000 Hydrogen 60,300

2nd 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 H


The association between the polar water molecules

Weak hydrogen

bonds


Comparing molecules

-61-8634H2SHydrogen sulphide

+19-9220HFHydrogen fluoride

+100018H2OWater

-33-7817NH3Ammonia

-161-18416CH4Methane

Boiling point / °C

Melting point/ °C

Molecular mass

FormulaMolecule

Compared to molecules of similar size and properties water has a very high melting point and boiling point


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


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


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


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


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)


Giant red wood Sequoiadendron giganteum

California USA

Public Domain image

Eucalyptus

grandis

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 © Shirley Burchill 2007

Water skater

Gerris gibbifer


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

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

Documents

From molecules to cells © 2007 Paul Billiet ODWSODWS