OAT Natural Sciences cheat sheet

Cell theory: all living things are made of cells, the cell is the basic unit of life, and all cells arise from pre-existing cells by division.

Prokaryotes lack a membrane-bound nucleus and organelles; they have a single circular chromosome, 70S ribosomes, and divide by binary fission.

Eukaryotic organelles: mitochondria and chloroplasts carry their own DNA and ribosomes (endosymbiotic theory); rough ER modifies proteins, smooth ER synthesizes lipids.

Osmosis: water moves from low to high solute concentration across a semipermeable membrane; hypertonic solution causes cell shrinkage (crenation in animal cells, plasmolysis in plant cells).

Enzyme kinetics: Michaelis-Menten v = Vmax[S]/(Km+[S]); Km equals the substrate concentration at half Vmax and is inversely related to enzyme affinity.

Competitive inhibitors raise apparent Km with unchanged Vmax; noncompetitive inhibitors lower Vmax with unchanged Km.

DNA replication is semiconservative; helicase unwinds, DNA polymerase synthesizes 5' to 3', and leading strand is continuous while lagging strand forms Okazaki fragments.

Mendelian genetics: monohybrid cross of heterozygotes gives 3:1 phenotype and 1:2:1 genotype; dihybrid cross of heterozygotes gives 9:3:3:1 with independent assortment.

Cellular respiration yields about 36-38 ATP per glucose: glycolysis (2 ATP, cytoplasm), Krebs cycle (mitochondrial matrix), and oxidative phosphorylation (inner membrane).

Ideal gas law PV = nRT with R = 0.0821 L·atm/(mol·K) or 8.314 J/(mol·K); STP means 0 °C and 1 atm, where 1 mol occupies 22.4 L.

Molarity M = moles solute / liters solution; dilution obeys M1V1 = M2V2; molality uses kg solvent and is temperature-independent.

pH = -log[H+]; pOH = -log[OH-]; pH + pOH = 14 at 25 °C; strong acid fully dissociates while weak acid uses Ka.

Henderson-Hasselbalch: pH = pKa + log([A-]/[HA]); buffer capacity is greatest when pH equals pKa.

Le Chatelier's principle: adding reactant shifts right, increasing pressure shifts toward fewer gas moles, and raising temperature favors the endothermic direction.

Equilibrium constant expressions exclude pure solids and liquids; K > 1 favors products, K < 1 favors reactants.

Thermodynamics: ΔG = ΔH - TΔS; a reaction is spontaneous when ΔG < 0, and ΔG° = -RT ln K.

Periodic trends: atomic radius decreases across a period and increases down a group; ionization energy and electronegativity increase across and decrease down.

Colligative properties depend on particle count: boiling point elevation ΔTb = iKb·m and freezing point depression ΔTf = iKf·m.

Hybridization: four groups = sp3 (109.5°), three groups = sp2 (120°, planar), two groups = sp (180°, linear).

IUPAC naming: identify the longest carbon chain, number to give the lowest locants to principal functional groups, then alphabetize substituents.

Functional group priority for naming: carboxylic acid > ester > amide > nitrile > aldehyde > ketone > alcohol > amine > alkene/alkyne > alkane.

Nucleophilic substitution: SN1 proceeds via carbocation (favored by tertiary substrates and polar protic solvents) with racemization; SN2 is concerted and backside with inversion, favored by primary substrates.

Elimination competes with substitution: E1 shares the carbocation intermediate with SN1; E2 is concerted, requires anti-periplanar geometry, and is favored by strong bulky bases.

Markovnikov's rule: H adds to the carbon with more hydrogens; anti-Markovnikov occurs with HBr and peroxides (radical mechanism) or hydroboration-oxidation.

Oxidation states: primary alcohol to aldehyde to carboxylic acid; secondary alcohol to ketone; tertiary alcohol resists oxidation.

Aromaticity requires a planar cyclic conjugated system with 4n+2 pi electrons (Hückel's rule); benzene has 6 pi electrons.

Chirality: a carbon with four different substituents is a stereocenter; R/S assignment uses Cahn-Ingold-Prelog priority by atomic number.