“Life began in water and it has been inextricably tied to water ever since.”

BIOCHEMISTRY IS WET CHEMISTRY

ALL METABOLISM OCCURS IN WATER

Water & The Fitness Of The EnvironmentWater & The Fitness Of The Environment

A classic book written by LAWRENCE HENDERSON discusses how earth is the only planet in the solar system on which

water naturally occurs in all three states…making life as we know it possible.

Figure 3.0 Earth

FITNESS OF THE ENVIRONMENTFITNESS OF THE ENVIRONMENT3/4 of earth covered with water

unicellular organisms are completely surrounded by water

most cells contain 70-99% water

H2O is the only element to occur in all 3 states within the range of earth temperatures.

WATERWATERINTRAMOLECULAR BONDING

Polar covalent bonds between O and H’s

INTERMOLECULAR INTERACTIONS Hydrogen bonds

WEAK BOND ENERGY 4-5 kcal/mol TRANSIENT - made and broken every .00000000001 seconds

Many properties of water are the result of H-Many properties of water are the result of H-bondingbonding

Cohesion & surface tension

High specific heatEvaporative coolingExpansion during

freezing ice floats

VERSATILE SOLVENTVERSATILE SOLVENTSOLUTION - homogenous mixtureSOLVENT - dissolving substanceSOLUTE - substance dissolved

Do you know what Do you know what determines solubility?determines solubility?

HYDROPHILICHYDROPHILICwater loving molecules have polarity or charge

interact freely w/ h2o soluble

includes ions, sugars, proteins & nucleic acids

Figure 3.7 A crystal of table salt dissolving in water

HYDROPHOBICHYDROPHOBICHydrophobic molecules are

nonpolar, nonionic molecules

&insoluble in water

e.g. lipids, plastics, rain slickers, gases,

hydrocarbons

Hydrophobic interactions are essential in Hydrophobic interactions are essential in the formation of membranesthe formation of membranes

HYDROPHOBIC INTERACTIONSHYDROPHOBIC INTERACTIONSSoaps and Detergents

Organic Salt + fatty acids

Form a film at the surface

Form micelles under the surface

pH & molaritypH & molarity

Unnumbered Figure (page 47) Chemical reaction: hydrogen bond shift

Figure 3.9 The pH of some aqueous solutions

Cells are extremely sensitive to changes in pH

To understand To understand biochemistry we biochemistry we needneed to know to know

a few things about a few things about

Acids, Bases and Acids, Bases and pHpH

ACIDACIDIncreases the relative [H+] of in

aq. solution.

also removes OH- via association

Acids are proton donors

e.g. HCl, H2SO

4, H

2PO

4

Figure 2.0 Bombardier beetle

Formic acid Ouch!

BASEBASEreducereduce the relative [H+] of a solution.

Or may increase [OH-

]

Bases are proton Bases are proton acceptorsacceptors

reduce [H+] indirectly

E.G. NaOH NH3 HCO

3

-

DISSOCIATION OF WATER MOLECULESin distilled water the number of H+ and OH-

ions in soln. at any given time is a constant

IONIZATION CONSTANT OF WATER

=10-7

Unnumbered Figure (page 47) Chemical reaction: hydrogen bond shift

This is what water does - continuously binding and dissociating

pHpH

simplified measure of the hydrogen ions in solution

pH = -log of [H+]

pHpHlogarithm (base 10)

1 pH unit = 10 fold change in H+ conc.

inverse relationship between pH/H+

> pH < [H+]

pH test questionpH test questionHow much greater is the [H+] in a solution with pH 2 than a solution with pH 6?

Answer: 104 or 10,000x

IMPORTANCE OF pHIMPORTANCE OF pHpH is vital to the shape/function of

proteinsespecially enzymes that control

metabolismalterations in pH disrupt H-bonding and

change the shape of protein molecules

BIOLOGICAL pH 6-8 (safe range)

BUFFERSBUFFERShelp maintain pHweak acid + weak

basereservoir for H+

(think sponge)

The carbonic acid buffering system helps to maintain the pH of the blood

Acid RainAcid precipitation threatens the fitness of

the environment

Major source - combustion of fossil fuels by industry & autos.

pH < than 5.6

as low as 1.5 in West Virginia

“The Challenge of Acid Rain” Scientific American, August, 1988.

Figure 3.10x1 Pulp mill

Figure 3.10x2 Acid rain damage to statuary, 1908 & 1968

Figure 3.10 The effects of acid precipitation on a forest