The Chemistry of Life

Why do we study chemistry? Chemistry is the foundation for Biology!

The World of Elements About 25 elements are essential for life 4 elements make up about 96% of living matter carbon (C) hydrogen (H) oxygen (O) nitrogen (N) 6 elements make up most of the remaining 4% sodium (Na) magnesium (Mg) phosphorus (P) sulfur (S) potassium (K) calcium (Ca) (iron … Fe) CHPS Na Mg K Ca NO Carbs Lipids Proteins Nucleic acids Phospholipds Nucleic acids Bones Nerve impulses Proteins Nucleic acids Circulation Digestion Immune systems Nerve impulses Muscles

Elements & their valence shells Elements in the same column have the same valence & similar chemical properties

Chemical reactivity Atoms want to have a full or complete valence shell Two ways to achieve this: ◦Gain/lose electrons ◦Share electrons – This tendency drives chemical reactions… and creates bonds

Bonds in Biology Weak bonds: ◦hydrogen bonds ◦Attraction between + and - ◦hydrophilic & hydrophobic interactions ◦Interactions with H 2 O ◦van derWaals forces ◦ionic Strong bonds: ◦covalent ◦sharing electrons Hydrogen bond Covalent bond I’m feeling bonded to you

Nonpolar covalent bond Pair of electrons are shared equally by 2 atoms ◦Example: hydrocarbons = C x H x ◦Methane (CH 4 ) balanced, stable, good building block Lots of energy to release Lots of stored energy Will become the structural base for carbohydrates & lipids * ENERGY *

Polar covalent bond Pair of electrons are shared UNequally by 2 atoms ◦Example: water = H 2 O ◦Oxygen has a stronger “attraction” for the electrons ◦Has a higher electronegativity ◦Water is a polar molecule ◦+ vs – poles ◦Leads to many interesting properties of water … H H Oxygen – – – – + +

Hydrogen bonds Found between polar molecules involving H ◦Example: water ◦Attraction between positive H in one H 2 O to negative O in another H 2 O ◦Can also occur wherever an –OH exists in a large molecule Weak bond ◦Common in biology H O H H bonds

Let’s take a look at water … the elixir of life!

Why study water? All life occurs in water ◦It’s found inside & outside the cell

The Chemistry of Water H 2 O molecules form H- bonds with each other ◦+H attracted to –O ◦Creates a “sticky” molecule

The Chemistry of Water Special properties of water ◦Cohesion & adhesion ◦Surface tension, capillary action ◦Good solvent ◦Many molecules dissolve in H 2 O ◦Lower density as a solid ◦Ice floats! ◦High specific heat ◦Water stores heat ◦High heat of vaporization ◦heats & cools slowly Ice.. Ice, Baby ….

Cohesion & Adhesion Cohesion ◦H bonding between H 2 O molecules ◦Water is “sticky” ◦Surface tension Adhesion ◦H bonding between H 2 O & other substances ◦Capillary action ◦Meniscus Think: Adhesive tape

How does H 2 O move towards the top of tree? Transpiration works with cohesion & adhesion

Water is the solvent of life Polarity makes H 2 O a good solvent ◦Polar H 2 O molecules surround + and – ions

What dissolves in water? Hydrophilic ◦Substances have attraction to H 2 O ◦polar or nonpolar??

What doesn’t dissolve in water? Hydrophobic ◦Substances that don’t have an attraction to H 2 O ◦polar or nonpolar?? I’m feeling kinda fatty …

The special case of ice Most substances become more dense as a solid, but not water ◦Ice floats! ◦H bonds form a crystal And this has made all the difference!

Specific heat H 2 O resists changes in temperature ◦High specific heat ◦Takes a lot to heat it up ◦Takes a lot to cool it down H 2 O moderates temperatures on Earth Specific heat & climate Important for me too - outside & inside my body

Specific heat Amniotic fluid acts as a temperature buffer for a developing fetus

Heat of vaporization Amount of energy required to turn a substance from liquid to gas Evaporative cooling Organisms rely on heat of vaporization to remove body heat

Ionization of water & pH Water ionizes ◦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 pH scale ◦Measures [H+] ◦How acidic or basic a solution is ◦0  7  14 H 2 O  H + + OH –

pH Scale tenfold change in H+ ions pH1  pH  times less H + pH8  pH  times more H + pH10  pH  times more H + 10 –1 H + Ion Concentration Examples of Solutions Stomach acid, Lemon juice 1 pH 10 0 Hydrochloric acid0 10 – –3 Vinegar, cola, beer 3 10 –4 Tomatoes 4 10 –5 Black coffee, Rainwater 5 10 –6 Urine, Saliva 6 10 –7 Pure water, Blood 7 10 –8 Seawater 8 10 –9 Baking soda 9 10 –10 Great Salt Lake –11 Household ammonia –12 Household bleach –13 Oven cleaner –14 Sodium hydroxide14

Buffers & Cellular Regulation pH of cells must be kept ~ 7 ◦pH affects shape of molecules ◦Shape of molecules affects function Control pH by buffers ◦H+ reservoir ◦Donates H+ when [H+] falls ◦Absorbs H+ when [H+] rises Amount of base added Buffering range 452 pH

Any Questions?

Homework Pick any specific terrestrial or aquatic animal and list the ways that water is important to its survival. Relate your list to the properties discussed today. ◦Cohesion & adhesion ◦Good solvent ◦Lower density as a solid ◦High specific heat ◦High heat of vaporization ◦pH