biologically important molecules. i.water biologically important molecules i.water a. structure -...

Biologically Important Molecules


I.Water


I.WaterA. Structure

- polar covalent bonds


I.WaterA. Structure

- polar covalent bonds - partial charges


I.WaterA. Structure

- polar covalent bonds - partial charges - hydrogen bonds

I. WaterA. StructureB. Properties

- 1. cohesion“water sticks to itself through H-bonds”

I. WaterB. Properties - 2. adhesion

“water sticks to other charged surfaces”

I. WaterB. 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.


capillary action surface tension – water molecules at the air/water/surface interface will form a bonded layer


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.


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).


capillary action surface tensionHydrodynamics – why are fish oily?


capillary action surface tensionHydrodynamics – why are fish oily? One reason is to reduce surface tension and drag

Newest suits are woven threads of hydrophobic polyurethane

I. WaterB. 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. WaterB. 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. WaterB. 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!)




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”

49.16 N

Temperature Range: -12 – 20 = 32oC Temperature Range: 4 – 18 = 14oC

Note difference in the scales of the x-axes….

I. WaterB. 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.




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.




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. WaterB. Properties - 5. Density-temperature relationship

From: http://www.marietta.edu/~mcshaffd/aquatic/sextant/physics.htm

Water is most dense at 4oC.

So, ice floats and can be melted by sun

I. WaterB. 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. WaterB. 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.


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’


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. WaterB. 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.


In all aqueous solutions at 25oC,The product of [H+][OH-] = 1 x 10-14

So, if the pH is 6.0, the concentration ofOH- ions is 1 x 10-8


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).





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 Bicarbonate H2CO3 HCO3- + H+

I. WaterC. Water and Life

Why Life on Earth in Water?

I. WaterC. 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.

biologically important molecules. i.water biologically important molecules i.water a. structure -...

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