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“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