Water to solid wetting capillary attraction individual

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Unformatted text preview: ino & alcohol side groups are ∂+ ß =O of carbonyl groups are ∂– Many of water’s unique properties relate to hydrogen bonds formed among these small polar molecules • Solvent power (water to solute) • Cohesion (water to solid) – Wetting & capillary attraction • Individual H-bond is very weak, but many combine to stabilize 3-D structure of biological macromolecules • Adhesion (water to water) – Surface tension & column tension – High heat capacity & heat of vaporization – Liquid density > solid density – Important for protein shape, DNA, etc. Hydrogen bonds Dissociation of Water • 1 out of 500,000,000 water molecules ionizes: H2O fiHydrogen+ OH– H+ Hydroxide ion ( = 1 p+ ) ion • = 6x1016 per liter of water = 10–7 moles per liter • Hence, neutral water contains: 10–7M H+ + 10–7M OH– • And [H+] = [OH–] • pH = –log [H+] = –log (10–7M ) = 7 Heyer Acids & Bases • So, in a neutral solution, [H+] = [OH–]; pH = 7.00 • An Acid is a compound that adds extra H+ to the solution. I.e., “H+ donor” • Thus, an acidic solution has [H+] > [OH–] pH < 7 (0.00–6.99) • A Base is a compound that removes H+ from the solution. I.e., “H+ acceptor” • Thus, an basic (alkaline) solution has [H+] < [OH–] pH > 7 (7.01–14.00) • ÍpH = Èacidity & ÈpH = Íacidity (Note: normal blood pH is 7.35 –7.45 — slightly basic!) 5 Biological Chemistry Effects of pH on Bioactivity • Relative amount of H+ in solution (i.e., the pH) can alter the charge and polarity of other solutes. • Â ∆ ionic or hydrogen bonds fl ∆ folding & 3-dimensional shape of large organic solutes (esp. proteins) • Â ∆ 3-dimensional shape fl ∆ biological activity of those organic molecules. • Â even small ∆pH can have major impacts on biological activity. Buffers • System of molecules and ions that act to prevent changes in [H+]. ‡ Stabilizes pH of a solution. • Blood bicarbonate buffer system: H20 + C02 Û H2C03 Û H+ + HC03– bicarbonate ion – Reaction can proceed in either direction depending upon the concentration of molec...
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This note was uploaded on 09/02/2011 for the course BIOL 6B taught by Professor Heyer during the Spring '10 term at DeAnza College.

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