The Chemistry of Life 2009-2010

Why are we studying chemistry? Chemistry is the foundation of Biology

The World of Elements H C N O Na Mg P S K Ca About 25 elements are essential for life Four elements make up 96% of living matter: • carbon (C) • hydrogen (H) • oxygen (O) • nitrogen (N) Six elements make up most of remaining 4%: • phosphorus (P) • calcium (Ca) • sulfur (S) • potassium (K) • magnesium (Mg) • sodium (Na)

Elements & their valence shells Elements in the same column have the same valence & similar chemical properties ELECTRONEGATIVITY Oxygen has medium electronegativity so doesn’t pull electrons all the way off hydrogen whereas chlorine would. So oxygen forms a polar covalent bond. Carbon has only a weak electronegativity so forms a nonpolar covalent bond

This tendency drives chemical reactions… Chemical reactivity Atoms tend to complete a partially filled valence shell or empty a partially filled valence shell This tendency drives chemical reactions… and creates bonds Ionic or Covalent bonds – –

Bonds in Biology Weak bonds Strong bonds Hydrogen bond hydrogen bonds H2O Weak bonds hydrogen bonds attraction between + and – hydrophobic & hydrophilic interactions interactions with H2O ionic Strong bonds covalent bonds sharing electrons H2O Covalent bond – H2 (hydrogen gas)

Nonpolar covalent bond Pair of electrons shared equally by 2 atoms example: hydrocarbons = CxHx methane (CH4 ) Lots of energy stored… & released Pair of electrons shared equally by 2 atoms strong stable bond example: hydrocarbons = CxHx methane (CH4 ) balanced, stable, good building block

Polar covalent bonds Pair of electrons shared unequally by 2 atoms example: water = H2O oxygen has stronger “attraction” for the electrons than hydrogen oxygen has higher electronegativity water is a polar molecule + vs – poles leads to many interesting properties of water… H Oxygen + – – Pair of electrons shared unequally by 2 atoms strong but interactive bond example: bonds within water = H2O oxygen has stronger “attraction” for the electrons than hydrogen oxygen has higher electronegativity water is a polar molecule + vs – poles leads to many interesting properties of water… – – +

Hydrogen bonding Polar water creates molecular attractions Weak bond attraction between positive H in one H2O molecule to negative O in another H2O also can occur wherever an -OH exists in a larger molecule Weak bond but common in biology H bonds H O APBio/TOPICS/Biochemistry/MoviesAP/03_02WaterStructure_A.swf attraction between H+ in one molecule to O- in another molecule weak bond example: bonds between water molecules leads to many interesting properties of water

Water Molecule and Polarity Video

Chemistry of Life Properties of Water 2010-2011

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

Chemistry of water H2O molecules form H-bonds with each other +H attracted to –O creates a sticky molecule APBio/TOPICS/Biochemistry/Movies AP/hydrogenbonds-Thinkwell.swf

Liquid of Life Special properties of water 1. cohesion & adhesion surface tension, capillary action 2. good solvent many molecules dissolve in H2O 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!

Try that with flour… or sugar… 1. Cohesion & Adhesion Cohesion H bonding between H2O molecules water is “sticky” surface tension (water pushed together to form a layer) Water beading up or raindrops Adhesion H bonding between H2O & other substances capillary action water climbs up paper towel, straw or cloth Try that with flour… or sugar… Cohesion H bonding between H2O molecules water is “sticky” surface tension capillary action drinking straw Adhesion H bonding between H2O & other substances meniscus water climbs up paper towel or cloth

2. Water is the solvent of life Polarity makes H2O a good solvent polar H2O molecules surround + & – ions solvents dissolve solutes creating solutions 2. Water is a good solvent = the solvent of life Polarity makes H2O a good solvent polar H2O molecules surround + & – ions solvents dissolve solutes creating solutions What dissolves in water easily? polar or non-polar molecules? How about oxygen -- does that dissolve in H2O?

What dissolves in water? Hydrophilic substances have attraction to H2O polar or non-polar? Hydrophilic substances have attraction to H2O

What doesn’t dissolve in water? Hydrophobic substances that don’t have an attraction to H2O polar or non-polar? Oh, look hydrocarbons! Hydrophobic substances that don’t have an attraction to H2O fat (triglycerol)

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

Why is “ice floats” important? Oceans & lakes don’t freeze solid surface ice insulates water below allowing life to survive the winter if ice sank… ponds, lakes & even oceans would freeze solid in summer, only upper few inches would thaw Oceans & lakes don’t freeze solid surface ice insulates water below allowing life to survive the winter if ice sank… ponds, lakes & even oceans would freeze solid in summer, only upper few inches would thaw seasonal turnover of lakes sinking cold H2O cycles nutrients in autumn

4. High Specific heat H2O resists changes in temperature Highest specific heat capacity of any liquid takes a lot to heat it up takes a lot to cool it down Helps organisms maintain a constant body temperature Specific heat H2O resists changes in temperature high specific heat = heats & cools slowly takes a lot to heat it up takes a lot to cool it down H2O moderates temperatures on Earth

5. Heat of vaporization Water also has a high heat of vaporization- takes a long time to change state from liquid to gas As water molecules evaporate, the surface they evaporate from gets cooler, a process called evaporative cooling.  In humans and other organisms, the evaporation of sweat, which is 90% water, cools the body to maintain a steady temperature.

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

Ionization of water & pH Water ionizes H+ splits off from H2O, leaving OH– if [H+] = [-OH], water is neutral if [H+] > [-OH], water is acidic if [H+] < [-OH], water is basic pH scale how acid or basic solution is 1  7  14 Water ionizes H+ splits off from H2O, leaving OH– H2O  H+ + OH– if [H+] = [-OH], water is neutral if [H+] > [-OH], water is acidic if [H+] < [-OH], water is basic pH scale how acid or basic solution is 1  7  14 H2O  H+ + OH–

cellular regulation pH of cells must be kept ~7 pH affects shape of molecules shape of molecules affect function therefore pH affects cellular function Exercise = acidic in muscles CO2 = carbonic acid lactic acid body uses buffers to counter act this

Any Questions? Do one brave thing today…then run like hell! He’s gonna earn a Darwin Award! Any Questions? Do one brave thing today…then run like hell! 2009-2010