Biologically Important Molecules
Biologically Important Molecules
I. Water
Biologically Important Molecules
I. Water
A. Structure
- polar covalent bonds
Biologically Important Molecules
I. Water
A. Structure
- polar covalent bonds
Biologically Important Molecules
I. Water
A. Structure
- polar covalent bonds
- partial charges
Biologically Important Molecules
I. Water
A. Structure
- polar covalent bonds
- partial charges
- hydrogen bonds
I. Water
A. Structure
B. Properties
- 1. cohesion
“water sticks to itself through H-bonds”
I. Water
B. Properties
- 2. adhesion
“water sticks to other charged surfaces”
I. Water
B. Properties
- consequences of cohesion/adhesion
Capillary action – rotating water
water molecules stick to the inner
surface of thin tubes, and act as a
fulcrum for other water molecules
that can spin and contact the
surface above them… through
cohesion, those in contact with
the new surface are themselves a
surface for now water molecules
to attach.
- important in the mvmt
of soil water up from the water
table to the root zone, and up
vascular plants in xylem tissue.
I. Water
B. Properties
- consequences of cohesion/adhesion
capillary action
surface tension – water molecules at the
air/water/surface interface will form a bonded
layer
I. Water
B. Properties
- consequences of cohesion/adhesion
capillary action
surface tension – water molecules at the
air/water interface will form a bonded layer
Detergents break this layer with a non-polar
fatty acid tail and a polar, hydrophilic sulfur
head.
I. Water
B. Properties
- consequences of cohesion/adhesion
capillary action
surface tension – water molecules at the
air/water interface will form a bonded layer
Detergents break this layer with a non-polar
fatty acid tail and a polar, hydrophilic sulfur
head.
This same principle allows oils to dissolve (or
be suspended) in water, in the presence of a
detergent (soap).
I. Water
B. Properties
- consequences of cohesion/adhesion
capillary action
surface tension
Hydrodynamics – why are fish oily?
I. Water
B. Properties
- consequences of cohesion/adhesion
capillary action
surface tension
Hydrodynamics – why are fish oily? One
reason is to reduce surface tension and drag
Newest suits are woven threads of
hydrophobic polyurethane
I. Water
B. Properties
- 3. High specific heat
‘specific heat’ is the amount of energy change required to change the
temperature of 1 g of that substance 1oC. By definition, a calorie is a change
in heat energy needed to change 1ml (or g) of water 1oC. (Dietary “calories” are
usually kilocalories).
I. Water
B. Properties
- 3. High specific heat
‘specific heat’ is the amount of energy change required to change the
temperature of 1 g of that substance 1oC. By definition, a calorie is a change
in heat energy needed to change 1ml (or g) of water 1oC. (Dietary “calories” are
usually kilocalories).
Water has a high specific heat because of the hydrogen bonds, which must be
broken before the molecules can move faster (increase temperature).
I. Water
B. Properties
- consequences of water’s high specific heat
Water is an excellent thermal buffer - aqueous solutions change
temperature more slowly than air (less dense aqueous solution).
I. Water
B. Properties
- consequences of water’s high specific heat
Water is an excellent thermal buffer - aqueous solutions change
temperature more slowly than air (less dense aqueous solution).
So, aqueous environments are more thermally stable (air temps vary more
dramatically than water temps…)
I. Water
B. Properties
- consequences of water’s high specific heat
Water is an excellent thermal buffer - aqueous solutions change
temperature more slowly than air (less dense aqueous solution).
So, aqueous environments are more thermally stable (air temps vary more
dramatically than water temps…)
So, terrestrial organisms change temperature more slowly than the
environment, giving them time to adjust behaviorally (like leaving!)
I. Water
B. Properties
- consequences of water’s high specific heat
Water is an excellent thermal buffer - aqueous solutions change
temperature more slowly than air (less dense aqueous solution).
So, aqueous environments are more thermally stable (air temps vary more
dramatically than water temps…)
So, terrestrial organisms change temperature more slowly than the
environment, giving them time to adjust behaviorally (like leaving!)
Large water bodies dampen temperature oscillations on neighboring land
masses – “maritime climates” and less variable than “continental climates”
Note difference in the scales of the x-axes….
49.16 N
Temperature Range: -12 – 20 = 32oC
Temperature Range: 4 – 18 = 14oC
I. Water
B. Properties
- 4. High heat of vaporization
Quantity of heat a liquid must absorb for 1 g of it to change to a gas.
Water’s high heat of vaporization means that:
- water doesn’t change state quickly; it can absorb a lot of energy
without changing state.
I. Water
B. Properties
- 4. High heat of vaporization
Quantity of heat a liquid must absorb for 1 g of it to change to a gas.
Water’s high heat of vaporization means that:
- water doesn’t change state quickly; it can absorb a lot of energy
without changing state.
- when it does change state, the most energetic molecules
evaporate and leave the liquid (or surface); so the average
kinetic energy (temperature) of the liquid or surface drops
dramatically – this is evaporative cooling.
I. Water
B. Properties
- 4. High heat of vaporization
Quantity of heat a liquid must absorb for 1 g of it to change to a gas.
Water’s high heat of vaporization means that:
- water doesn’t change state quickly; it can absorb a lot of energy
without changing state.
- when it does change state, the most energetic molecules
evaporate and leave the liquid (or surface); so the average
kinetic energy (temperature) of the liquid or surface drops
dramatically – this is evaporative cooling.
- evaporative cooling keeps water bodies cooler than air, and cools
living organisms (evapotranspiration, perspiration).
I. Water
B. Properties
- 5. Density-temperature relationship
Water is most
dense at 4oC.
So, ice floats
and can be
melted by sun
From: http://www.marietta.edu/~mcshaffd/aquatic/sextant/physics.htm
I. Water
B. Properties
- 5. Density-temperature relationship
Water is most
dense at 4oC.
So, ice floats
and can be
melted by sun
And ice acts as
an insulator,
reducing further
energy loss.
I. Water
B. Properties
- 6. solvent
Ionic and polar compounds dissolve in water
Salts dissolve in water when their
constituent ions separate and bond
to water molecules instead of each
other.
I. Water
B. Properties
- 6. solvent
Ionic and polar compounds dissolve in water
Salts dissolve in water when their
constituent ions separate and bond
to water molecules instead of each
other.
The water molecules surround the
charged substance as a ‘hydration
shell’
I. Water
B. Properties
- 6. solvent
Large molecules or their aggregates that can be
suspended in water, but do not dissolve, create colloids
Hydrophilic colloids can form because
the molecules react with water but are too
large to dissolve (cotton).
Emulsions are colloidal suspensions of
two two liquids that do not mix (dissolve)
together (oil and water).
(colloid)
I. Water
B. Properties
- 7. Water dissociates
Although the H+ is always bound to another water molecule (as a
hydronium ion), we represent it (H+) and it’s concentration as if it is
‘free’. In pure water, the concentration is 1 x 10-7.
I. Water
B. Properties
- 7. Water dissociates
In all aqueous solutions at 25oC,
The product of [H+][OH-] = 1 x 10-14
So, if the pH is 6.0, the concentration of
OH- ions is 1 x 10-8
I. Water
B. Properties
- 7. Water dissociates
Acids contribute H+ ions to a solution; bases absorb H+ from solution:
I. Water
B. Properties
- 7. Water dissociates
Acids contribute H+ ions to a solution; bases absorb H+ from solution:
HCl dissociates in water to: H+ and Cl-, adding H+ and lowering the pH
I. Water
B. Properties
- 7. Water dissociates
Acids contribute H+ ions to a solution; bases absorb H+ from solution:
HCl dissociates in water to: H+ and Cl-, adding H+ and lowering the pH
NH3 directly absorbs H+ in solution as NH4+, raising the pH
I. Water
B. Properties
- 7. Water dissociates
Acids contribute H+ ions to a solution; bases absorb H+ from solution:
HCl dissociates in water to: H+ and Cl-, adding H+ and lowering the pH
NH3 directly absorbs H+ in solution as NH4+, raising the pH
NaOH dissociates in water to: Na+ and OH-, and the OH- reacts with H+,
lower the concentration of H+ in the solution (and raising the pH).
I. Water
B. Properties
- 7. Water dissociates
Acids contribute H+ ions to a solution; bases absorb H+ from solution:
HCl dissociates in water to: H+ and Cl-, adding H+ and lowering the pH
NH3 directly absorbs H+ in solution as NH4+, raising the pH
NaOH dissociates in water to: Na+ and OH-, and the OH- reacts with H+,
lower the concentration of H+ in the solution (and raising the pH).
Buffers hold pH stable by absorbing excess H+ ions or donating H+ ions if
they are depleted.
Carbonic Acid
H2CO3
Bicarbonate
HCO3- + H+
I. Water
C. Water and Life
Why Life on Earth in Water?
I. Water
C. Water and Life
Life on Earth is inconceivable without water.
Life requires rapid and continuous chemical reactions
facilitated by a dissolution of reactants in a liquid solvent.
Water’s solvent properties are ideal.
Water is a liquid over a wide temperature range that is very
common on Earth. (High specific heat, vaporization).
Water is abundant on Earth, covering over 70% of the surface.
Water is a thermally stable internal/external environment.
No surprize that life probably originated in water, and did not
adapt to exploit the desiccating terrestrial environments
until the last 10% of Earth history.