Chemistry of Life Properties of Water Hydrogen bond

Chemistry of Life Properties of Water

Hydrogen bond Bonds in Biology H 2 O § Weak bonds u hydrogen bonds § attraction between + and – u § interactions with H 2 O u H 2 O hydrophobic & hydrophilic interactions Van der Waals forces Covalent bond § (-) and (+) regions of molecule attract u ionic § Strong bonds u covalent bonds § sharing electrons – – H 2 (hydrogen gas)

More about Water Why are we studying water? All life occurs in water u inside & outside the cell

Chemistry of water § H 2 O molecules form H-bonds with each other +H attracted to –O u creates a sticky molecule u

Elixir of Life § Special properties of water 1. cohesion & adhesion § surface tension, capillary action 2. good solvent § many molecules dissolve in H 2 O § hydrophilic vs. hydrophobic 3. lower density as a solid § ice floats! 4. high specific heat § water stores heat 5. high heat of vaporization § heats & cools slowly Ice! I could use more ice!

1. Cohesion & Adhesion § Cohesion u u H bonding between H 2 O molecules water is “sticky” § surface tension § drinking straw § Adhesion u Try that with flour… or sugar… H bonding between H 2 O & other substances § capillary action § meniscus § water climbs up paper towel or cloth

How does H 2 O get to top of trees? Transpiration is built on cohesion & adhesion

2. Water is the solvent of life § Polarity makes H 2 O a good solvent polar H 2 O molecules surround + & – ions u solvents dissolve solutes creating solutions u

What dissolves in water? § Hydrophilic substances have attraction to H 2 O u polar or non-polar? u

What doesn’t dissolve in water? § Hydrophobic substances that don’t have Oh, look an attraction to H 2 O hydrocarbons! u polar or non-polar? u fat (triglycerol)

3. The special case of ice § Most (all? ) substances are more dense § when they are solid, but not water… Ice floats! u H bonds form a crystal Ice! I could use more ice! And this has made all the difference!

Why is “ice floats” important? § Oceans & lakes don’t freeze solid u surface insulates water below § allowing life to survive the winter u if ice sank… § ponds, lakes & even oceans would freeze solid § in summer, only upper few inches would thaw u seasonal turnover of lakes § sinking cold H 2 O cycles nutrients in autumn

4. Specific heat § H 2 O resists changes in temperature high specific heat u takes a lot to heat it up u takes a lot to cool it down u § H 2 O moderates temperatures on Earth Specific heat & climate

5. Heat of vaporization Evaporative cooling Organisms rely on heat of vaporization to remove body heat

Ionization of water & p. H § Water ionizes u H+ splits off from H 2 O, leaving OH– § if [H+] = [-OH], water is neutral § if [H+] > [-OH], water is acidic § if [H+] < [-OH], water is basic § p. H scale how acid or basic solution is u 1 7 14 u H 2 O H+ + OH–

p. H Scale H+ Ion Concentration p. H Examples of Solutions 100 0 10– 1 1 10– 2 2 Stomach acid, Lemon juice 10– 3 3 Vinegar, cola, beer 10– 4 4 Tomatoes p. H 1 p. H 2 10 -1 10 -2 10– 5 5 Black coffee, Rainwater 10– 6 6 Urine, Saliva 10 times less H+ 10– 7 7 Pure water, Blood p. H 8 p. H 7 10 -8 10 -7 10– 8 8 Seawater 10– 9 9 Baking soda 10 times more H+ 10– 10 10 Great Salt Lake p. H 10 p. H 8 10 -10 10 -8 10– 11 11 Household ammonia 10– 12 12 Household bleach 10– 13 13 Oven cleaner 10– 14 14 Sodium hydroxide tenfold change in H+ ions 100 times more H+ Hydrochloric acid

Buffers & cellular regulation § p. H of cells must be kept ~7 p. H affects shape of molecules u shape of molecules affect function u therefore p. H affects cellular function u § Control p. H by buffers reservoir of H+ § donate H+ when [H+] falls § absorb H+ when [H+] rises 7 6 p. H u 9 8 Buffering range 5 4 3 2 1 0 0 1 2 3 4 5 Amount of base added

Moles and Molarity § Since most biochemical reactions occur in water u It is important to learn to calculate the concentration of solutes in an aqueous solution § Mole u Exact number of molecules of a substance in a given mass § Molarity Number of moles of solute per liter of solution Avogodro’s Number! u § u u 6. 02 x 1023 Weight of one mole of atoms

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