Buffers Buffers are solutions that resist changes in
Buffers • • Buffers are solutions that resist changes in their p. H 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 HA Acid • • H + + Aconjugate base 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 K a= [H ][A ] [HA] A solution of a weak acid that has a p. H near to its p. Ka has an equivalent amounts of conjugate base and weak acid. Typically a weak acid is in its useful buffer range within 1 p. H unit of its p. Ka.
Polyprotic acids • • • Have more than one acid-base group H 3 PO 4 and H 2 CO 3 The p. K’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 OO H-O-C-C-O-H p. K differs by 3 p. H units O O H-O-C-CH 2 -C-O-H p. K differs by 1. 4 p. H units
Polyprotic acids • • The effect of having successive ionizations from the same center is even greater. However if p. K’s of polyprotic acid differ by less than 2 p. H units, this reflects the average ionization of all of the groups.
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 • Humans • Plants H 2 S CH 2 O h So H 2 O + CO 2
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.
MW 18 -44 100 -250 N 2, H 2 O, CO 2 20 amino acids 100 -800 Amino acids 104 -109 106 -1010 Proteins 5 aromatic bases, ribose Nucleotides Nucleic acids Glucose Palmitate, glycerol, choline Sugars Phospholipids Polysaccharides Multienzyme complexes, ribosomes, chromosomes, membranes, structural elements Organelles, Cells, Tissues, Organsims
Universal features of cells (cont. ) • All cells function as biochemical factories and use the same basic molecular building blocks. • Proteins (amino acids – – – polypeptides proteins) 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) – – – •
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 (m. RNA, t. RNA, pre-m. RNA or hn. RNA, r. RNA) • Proteins and nucleic acids are produced by the same rules – Central dogma DNA RNA • A living cell can exist with fewer than 500 genes! Protein
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 Eukaryotes Bacteria, Archaea Fungi, Protists, Animals, Plants 1 -10 µm 10 -100 µm
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
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