1. Buffers Buffers are solutions that resist changes in their pH as acid (H+) or base (OH-) is added. Typically, buffers are composed of a weak acid and its conjugate base. Acids = Proton (H+) donors Bases = Proton Acceptors Acids and their conjugate bases are in equilibrium. Equilibria are related to the properties of the reactants and products, so for weak acids, the tendency to give up its proton determines its buffering property The tendency to ionize can be put in an equilibrium equation A solution of a weak acid that has a pH near to its pK a has an equivalent amounts of conjugate base and weak acid. Typically a weak acid is in its useful buffer range within 1 pH unit of its pK a. [H + ][A - ] Ka=Ka= [HA] HA H + + A - Acid conjugate base

2. Polyprotic acids Have more than one acid-base group H 3 PO 4 and H 2 CO 3 The pK’s of two closely associated acid-base groups are not independent - the closer they are, the greater the effect. –Examples: oxalic acid and succinic acid H-O-C-C-O-H H-O-C-CH 2 CH 2 -C-O-H O O OO pK differs by 3 pH units pK differs by 1.4 pH units

3. Polyprotic acids The effect of having successive ionizations from the same center is even greater. However if pK’s of polyprotic acid differ by less than 2 pH units, this reflects the average ionization of all of the groups.

4. Universal features of cells “Life possesses the properties of replication, catalysis, and mutability.” - Norman Horowitz Life requires free energy. –Main energy currency is ATP (bond energy,  G) NADH, NADPH (redox energy) –All cells obey the same laws of thermodynamics (see Ch.3).  G (Gibbs free energy) must be negative (spent)  S (Entropy) increases –Sources of energy may vary Purple sulfur bacteria H 2 S S o HumansCH 2 OH 2 O + CO 2 Plantsh

5. Universal features of cells (cont.) Most organisms are composed of only 16 chemical elements (H,C,N,O,P,S,Mn, Fe, Co, Cu, Zn, Na, Mg, Cl, K, Ca). –Chemical makeup appears to be determined partly by the availability of raw materials and the specific roles of of molecules in life processes. –Do not reflect the composition of the biosphere –Examples on per atom basis, H in organisms = 49%, H in Earth’s crust = 0.22 %, Si in organisms = 0.033%, Si in Earth’s crust = 28%) H, O, N, and C, make up >99% by weight of living matter are the smallest atoms that can share 1, 2, 3, and 4 electrons respectively. O, N, and C are the only elements that easily form strong multiple bonds. O 2 is soluble in water and readily available to all organisms. Phosphorous and sulfur are unstable in the presence of water. –Require a large amount of energy to form. –Energy released when they are hydrolyzed.

6. N 2, H 2 O, CO 2 20 amino acids 5 aromatic bases, ribose Glucose Palmitate, glycerol, choline Amino acids Nucleotides Sugars Phospholipids Proteins Nucleic acidsPolysaccharides Multienzyme complexes, ribosomes, chromosomes, membranes, structural elements Organelles, Cells, Tissues, Organs, Organsims MW 18-44 100-250 100-800 10 4 -10 9 10 6 -10 10

7. Universal features of cells (cont.) All cells function as biochemical factories and use the same basic molecular building blocks. Proteins (amino acidspolypeptidesproteins) –Can be structural or catalytic –Enzymes –Transport (Na+/K+ pump) –Storage (ferritin) –Signals (hormones/toxins), examples insulin or botulinum toxin –Receptors –Structure (collagen, elastin) Lipids (fatty acidslipids) –Membranes –Triglycerides (energy storage) –Phospholipds (membrane structure) –Sphingolipids (found in nerve cells and brain tissue) –Sterols (hormones and membranes)

8. Universal features of cells (cont.) Carbohydrates –Monosaccharides (glucose, fructose) –Disaccharides (sucrose, maltose) –Trisaccharides (raffinose) –Complex carbohydryates Starch (energy storage) Cellulose (structure, cell wall) Cell-cell recognition Nucleic acids –DNA (genetic material) –RNA (mRNA, tRNA, pre-mRNA or hnRNA, rRNA) Proteins and nucleic acids are produced by the same rules –Central dogma A living cell can exist with fewer than 500 genes! DNA RNA Protein

9. Types of cells There are two major cell types: eukaryotes and prokaryotes. Eukaryotes have a membrane enclosed nucleus encapsulating their genomic DNA. Prokaryotes do not have a nucleus. Prokaryotes Bacteria, Archaea 1-10 µm Eukaryotes Fungi, Protists, Animals, Plants 10-100 µm

10. Prokaryotes Most numerous and widespread organisms on Earth Wide variety of metabolic energy sources Relatively simple anatomy Shape is sometimes used to determine a particular type of bacteria