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 -

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

5. Water
Amphipathic molecules

6. Water

7. Water

8. Water

9. Water
WATER

10. Water
Water chain in cytochrome f

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

12. 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

13. 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-] = (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)

14. Acid/Base Pairs Acid Conjugate base HA+ H+ + A HA H+ + A-
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

15. pH of aqueous fluids

16. Conjugate acid-base pairs

17. Titration Curve
acetic acid

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

19. Buffering against pH changes
Buffers:
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

20. 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

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

22. Protein enzymes have an optimum pH for activity

23. 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

24. Water as a reactant
HYDROLYSIS
CONDENSATION