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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 &
– 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–
( = 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
• 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
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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.
- Spring '10
- molecular biology