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Water

Water. > 70% of weight of most organisms Polar molecules - hydrophilic Nonpolar molecules - hydrophobic Hydrogen bonds are ______ interactions compared to covalent bonds Each water (H 2 O) molecule can form H-bonds with 4 other waters. d +. d +. d -. d +. d -. d +. Water.

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Water

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  1. Water >70% of weight of most organisms Polar molecules - hydrophilic Nonpolar molecules - hydrophobic Hydrogen bonds are ______ interactions compared to covalent bonds Each water (H2O) molecule can form H-bonds with 4 other waters d+ d+ d- d+ d- d+

  2. Water Hydrogen bonding

  3. Water Amphipathic - contains regions that are polar (charged) and regions that are nonpolar

  4. Water Amphipathic molecules

  5. Water

  6. Water

  7. Water

  8. Water WATER

  9. Water Water chain in cytochrome f

  10. Ionization of Water H2O H+ + OH- H+ is a hydrogen ion OH- is a hydroxyl ion Actually 2H2O H3O+ + OH- H3O+ is a hydronium ion

  11. Ionization of Water H2O H+ + OH- Keq = [H+][OH-] / [H2O] [H2O] ~ 55.5 mol/L Keq = 1.8 x 10-16 Kw = (Keq) [H2O] Kw = (1.8 x 10-16) (55.5) So Kw = [H+][OH-] = 10-14 (mol/L)2 at 25˚ In pure water, [H+] = [OH-] = 10-7, a neutral solution pH = log (1/[H+]) = -log[H+] A neutral solution has a pH = 7.0 When [H+] > [OH-], pH < 7.0 (acidic) When [H+] < [OH-], pH > 7.0 (basic)

  12. Acid/Base Pairs Acid Conjugate base HA+ H+ + A HA H+ + A- HA - H+ + A2- For a strong acid, dissociation is complete so [H+] = [acid] and pH = -log [H+] For weak acid, dissociation is incomplete so Ka = [H+][A-] / [HA] Ka is acid dissociation constant pH is function of [acid] and Ka [H+] = Ka [HA] / [A-] -log[H+] = -logKa + log [A-] / [HA] pKa = -logKa pH = pKa + log [A-] / [HA] (Henderson-Hasselbach) The pK of an acid (base) is the pH at which the acid (base) is half dissociated

  13. pH of aqueous fluids

  14. Conjugate acid-base pairs

  15. Titration Curve acetic acid

  16. Titration Curve pK1 = a carboxyl group pK2 = a amino group

  17. Buffering against pH changes Buffers: mixtures of weak acids and their conjugate bases Resist changes in pH when small amounts of acid/base are added Maintenance of a specific and constant pH, near 7.0 is needed by cells and organisms - small changes in pH can have a large impact on rate of cellular processes

  18. Buffering against pH changes amino acid histidine - weak acid pKa = 6.0

  19. Protein enzymes have an optimum pH for activity

  20. Biological buffers - bicarbonate (phosphate too) Exercise lactic acid (H+) produced (pH of blood plasma lowered) reaction pushed to produce more CO2 - exhale Protein catabolism ammonia (NH3) produced and pH of blood plasma is raised Reaction pushed to create more H+ more CO2 from lungs dissolved in blood plasma RATE OF BREATHING keeps BLOOD PH CONSTANT

  21. Water as a reactant HYDROLYSIS CONDENSATION

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