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Chemistry of Life

Chemistry Cellular processes are based on physical and chemical changes – Respiration/Photosynthesis – Enzymatic Reactions – Diffusion/Osmosis – Blood pH buffering systems Organ system processes are also based on physical and chemical changes – Blood clotting (both physical and chemical) – Respiration (both physical and chemical) – Digestion (both physical and chemical) – Immunity (both physical and chemical) – Nervous system (both physical and chemical) – Muscle contraction (both physical and chemical) – Cell Division (both physical and chemical)

What’s Matter? Atoms – Building blocks of matter (elements, molecules) – More stable when the outer orbital (energy level) has 8 electrons (2 if H or He) – Orbitals (electron shells) 1 st – holds up to 2 electrons 2 nd – holds up to 8 electrons 3 rd – holds up to 18 electrons 4 th – holds up to 32 electrons – Sub-atomic particles Protons – Positive, 1 amu (mass unit), in nucleus Neutrons – No charge (neutral), 1 amu (mass unit), in nucleus Electrons – Negative, no mass (negligible), orbitals, determine reactivity of atom

Importance of Electrons! Energy Transfers – Electrons move from one orbital to another when energy is absorbed or lost – This allows for energy to be transferred from one molecule to another – Application: Photosynthesis – Sunlight energy excites electrons to “jump” to next orbital allowing for energy to be absorbed, rearranged, and converted into chemical energy

Chemical Bonds Covalent – Atoms share electrons to form stable molecules/compounds – Polar covalent Unequal sharing of electrons Ex: Water (dissolves other polar molecules) – The electrons spend more time near oxygen because of it high electronegativity – Non-polar covalent Electrons are equally shared – Atoms have similar electronegativity Ex: Fats/Oils and Phospholipids (dissolves other non-polar molecules) – Carbon and Hydrogen have similar electronegativity – Hydrophilic head; hydrophobic tail

Elements of the Human Body Note: Oxygen and Nitrogen have high electronegativity which means they like to “steal” electrons and thus typically form polar compounds! Carbs – CHO Proteins – CHONS Lipids – CHOP Nucleic Acids – CHNOP Calcium – muscle contractions Sodium/Potassium – nerve impulse

Ionic Bonds – Electrons are “given away” from one atom and “stolen” by another – Due to differences in electronegativity – Ionic compounds will completely dissociate in water and thus dissolve (Ex: salt) Chlorine is much more electronegative then sodium and thus has the ability to “steal” it’s electron Forms a cubic crystal lattice structure

Sugar vs. Salt Polar Covalent Dissolves in water (hydroxyl groups) Irregular crystal lattice structure (many isomers) Forms polysaccharides (starch, cellulose, glycogen) Non-conductor Burns easily (good fuel source for cells) Ionic Dissolves in water (electrolytes) Cubic crystal lattice structure Increases blood pressure Conducts electricity Very difficult to burn

Hydrogen Bonds – Results when hydrogen is bonded to 2 highly electronegative atoms at the same time Application: – Water molecules bonding to each other and other polar molecules – DNA – 2 strands linked together (nitrogenous bases) – Secondary, Tertiary, Quaternary structures of proteins

Water is wonderful … and unique! How do the unique chemical and physical properties of water make life on earth possible? Key concepts (pg. 50) Polar molecule – Results in hydrogen bonding Cohesion Adhesion Surface Tension Moderates temperature – High specific heat – Evaporative cooling Oceans don’t freeze solid Solvent

Polar bond (oxygen is more electronegative than hydrogen)

Hydrogen bond (hydrogen atom covalently bonds to two electronegative atoms) Each water molecule can bind with up to 4 other water molecules

Hydrogen bonding in water results in: Cohesion – Transport of water against gravity in plants – Water exiting the leaves “tugs” on water molecules leading all the way down to the roots Adhesion – Water clings to the walls (cellulose does not dissolve in water … nice quality) of plant vessels to help counter the downward pull of gravity Surface tension – Measure of how difficult it is to stretch or break the surface of a liquid – Some animals can stand, walk, or run on water

Solid water (ice) is less dense than liquid water. When water freezes the hydrogen bonds are “locked” into place and creates an organized crystal structure with air pockets that make it less dense.

Water moderates temperature Absorbs heat from air that is warmer – Hydrogen bonds break Releases heat to air that is cooler – Hydrogen bonds form High specific heat – This absorption and release of of heat from water only slightly changes its own temperature – Coastal areas generally have milder climates

Evaporative Cooling – Water molecules must have a relatively high kinetic energy to break hydrogen bonds and change states from liquid to gas – Contributes to stability temperature of lake and ponds – Prevents land organisms from overheating – Prevents tissues in leaves from becoming too warm in sunlight

Water is the solvent of life The oxygen (-) regions of water cling to sodium (Na + ) ions while the hydrogen (+) regions of water are attracted to chloride (Cl - ) ions. Eventually all ions are dissolved

The Dissociation of Water Molecules

Acid – Increases the hydrogen ion concentration Base – Reduces the hydrogen ion concentration – Increases the hydroxide ion concentration Logarithmic scale – pH 1 is 10 X more acidic than pH 2 pH = - log [H+] pH 7; [H+] = [OH-] = [H+] x [OH-] = If pH = 5 than [H+] = 5 and [OH-] = 9

Note: – Enzymes have optimal pH’s in which they work best – Pepsin is found in the stomach optimal pH is very acidic

pH Buffers Substances that minimize changes in concentrations of H+ and OH- in solution Accepts H+ ions from the solution when they are in excess and donates H+ ions to the solution when they are depleted Human blood pH stability – Uses Carbonic Acid – Bicarbonate buffering system H 2 CO 3 (carbonic acid) (H+ donor) HCO 3 - (bicarbonate ion (base)) (H+ acceptor) H + (hydrogen ion) + Response to rise in pH Response to drop in pH