Download Preview - ZigZag Education

OCR AS Biology
Unit F212
Molecules, Biodiversity, Food and Health
Module 1: Biological molecules
Introduction
 There are a number of key biological molecules that
have important roles within cells. These are
carbohydrate, protein, lipid (fats and oils) and nucleic
acids.
 Knowledge of their structure will help you understand
their functions.
Biological molecules
Nucleic acids
Enzymes
 Click on the button to select the topic
(Red links are disabled)
Biological molecules
Select topic by clicking on the button
 Water





Amino acids and protein structure
Carbohydrates
Lipids (fats and oils)
Chemical tests for key biological molecules
Summary
Water...
 Water is a key component of our cells
 Approximately 70% of the body is water
 It has a number of key roles




it acts as a solvent
chemical reactions/metabolism take place in solution
it has a cooling effect when it evaporates
cohesive forces exist between water molecules
 water flows!
 surface tension
... water...
 Water is a small molecule
δ+
 two hydrogen atoms
 covalently bonded to oxygen
H
δO
δ+
H
 Electrons are not shared
equally between the oxygen
and hydrogen
 the oxygen nucleus has 8
positively-charged protons
 more ‘pulling power’ than
the single proton of the
hydrogen
... water...
 Water molecule has a
dipole:
δ+
H
O
δ+
δ+
H
O
δ+
H
δ-
δ-
H
Hydrogen bond
 slight negative charge
around the oxygen
 slight positive charge
around the hydrogen
 Negatively-charged
oxygen is attracted to the
positively-charged
hydrogen
 forms weak hydrogen
bonds between the water
molecules
Properties of water...
Water has a number of important properties:
 good solvent
 liquid at biologically important temperatures
 cohesion and adhesion
 freezing and density
 thermal properties
 metabolism
 transport
Solvent...
 Water is a good solvent
 ions
 polar molecules
 Water molecules are attracted to the charged part of
solute molecules
 surround separate them from the rest
 enter solution
 Most metabolism takes place in solution
 Note: non-polar molecules do not interact with water
 tend to be pushed together away from the water
 helps stabilise membranes
 3D structure of globular proteins
Liquid...
 Water is a liquid at
biological temperatures
because of the formation
of hydrogen bonds
between water
molecules
 Each hydrogen bond is
quite weak, but
collectively strong
δ+
H
O
δ+
δ+
H
O
δ+
H
δ-
H
δ-
Cohesion...
 Water molecules stick to each other creating a
surface tension
 pond-skaters make use of this
 explains why there is a meniscus
 explains how water travels up fine xylem vessels
 the transpiration stream
 cohesion-tension
Freezing and density...
 As water cools
 density increases
 reaches its maximum density at 4oC
 colder water sinks
 Below 4oC water
 is less dense
 rises to the surface
 Further cooling causes ice to form
 this is less dense and floats
 insulates the water below
 water does not freeze to the bottom
 allows aquatic life to survive
Thermal properties...
 Temperature increases




water molecules move around
more kinetic energy
hydrogen bonds break, but they can and do reform
rather difficult for water molecules to escape the liquid
phase
 When water molecules have sufficient energy
 leave the liquid phase
 i.e. they evaporate
 take energy with them
 has a cooling effect
Thermal properties...
 Water has
 high specific heat capacity
 water can absorb a lot of heat energy without changing
temperature much
 high latent heat of vaporisation
 when it evaporates, takes a lot of heat energy with it
 Aquatic environments often have more stable
temperatures than terrestrial ones
 true for habitats close to large bodies of water
 think about maritime and continental climates
Metabolism...
 Water is involved in a number of chemical reactions
 hydrolysis of bonds during digestion
 see section on:
 protein
 lipid
 carbohydrate
 it is the source of H+ in photosynthesis
 it is produced during respiration
 can form a significant proportion of some animals’
water requirements
 kangaroo rat
 camel
Transport...
 Many water soluble molecules are transported in
solution
 Transport systems of animals and plants
 mammalian transport system contains blood
 blood plasma is principally water
 plants use mass flow
 transport materials in their vascular system
 In addition many materials are transported across
exchange surfaces in solution
Complete the table to summarise properties of water and their importance…
Property
Solvent
Liquid at
biological temp
Cohesion and
adhesion
Freezing
Thermal
Metabolism
Importance/explanation
Example
Property
Importance/explanation
Example
Solvent
Water molecules are attracted to
the charged part of solute
molecules.
Respiratory and photosynthetic
gases dissolve before entering
cells; digestion produces soluble
products; metabolism takes place
in solution.
Liquid at
Hydrogen bonding between the
Transport in plants and animals
biological temp water molecules mean it is liquid at requires liquid water!
biologically important temperatures
(0-100oC).
Cohesion and
adhesion
Water molecules stick together and Surface tension on water;
are attracted to surfaces.
transport of water in xylem relies
upon cohesion (and adhesion).
Freezing
Density changes as water freezes
– less dense, so ice floats (layer of
ice also insulates).
Water bodies freeze from the top
down. Lakes seldom freeze
completely; organisms survive in
the cold, deeper water.
Thermal
High specific heat capacity; high
latent heat of vaporisation.
Water temperature quite stable ;
evaporation has a cooling effect.
Metabolism
Metabolism takes place in
aqueous solution;
reactant/produced in some.
Hydrolysis; condensation; H2O
used in photosynthesis.