PA-CAT cheat sheet

Anatomical position: standing upright, feet parallel, palms facing anteriorly (supinated), thumbs directed laterally.

Sagittal plane divides left and right; coronal (frontal) plane divides anterior and posterior; transverse (axial) plane divides superior and inferior.

Brachial plexus roots are C5–T1; terminal branches are musculocutaneous, axillary, radial, median, and ulnar.

Femoral triangle borders: inguinal ligament (superior), sartorius (lateral), adductor longus (medial); contents lateral to medial are femoral nerve, artery, vein, empty space, lymphatics.

Cranial nerves with only sensory function: I, II, VIII; only motor: III, IV, VI, XI, XII; mixed: V, VII, IX, X.

Diaphragm apertures: inferior vena cava at T8, esophagus at T10, aorta at T12; phrenic nerve roots C3–C5.

Celiac trunk branches: left gastric, splenic, and common hepatic arteries.

Rotator cuff: supraspinatus (abduction), infraspinatus and teres minor (external rotation), subscapularis (internal rotation).

Cardiac output = heart rate × stroke volume; Fick principle: CO = VO2 / (CaO2 − CvO2).

Mean arterial pressure ≈ diastolic pressure + 1/3 (systolic − diastolic); it depends on cardiac output and total peripheral resistance.

Henderson–Hasselbalch: pH = 6.1 + log([HCO3−] / (0.03 × PaCO2)).

GFR = filtration coefficient × net filtration pressure; filtration fraction = GFR / renal plasma flow (normally ~0.20).

Aldosterone increases sodium reabsorption and potassium secretion in collecting duct principal cells; ADH increases water permeability via aquaporin-2.

Right shift of the oxyhemoglobin curve (↑CO2, ↑H+, ↑temperature, ↑2,3-BPG) decreases hemoglobin oxygen affinity and improves tissue oxygen unloading.

Frank–Starling relationship: increasing end-diastolic volume increases stroke volume up to a physiologic optimum.

Resting membrane potential (~−70 mV) is set mainly by potassium permeability; the action potential threshold is about −55 mV with rapid sodium influx.

Glycolysis net yield per glucose: 2 pyruvate, 2 ATP, 2 NADH; phosphofructokinase-1 is the rate-limiting enzyme.

Per acetyl-CoA in the TCA cycle: 3 NADH, 1 FADH2, 1 GTP; isocitrate dehydrogenase is rate-limiting.

Oxidative phosphorylation yields about 2.5 ATP per NADH and 1.5 ATP per FADH2, totaling ~30–32 ATP per glucose.

Michaelis–Menten: v = Vmax[S]/(Km + [S]); Km equals the substrate concentration at half-maximal velocity.

Competitive inhibition raises Km with unchanged Vmax; noncompetitive inhibition lowers Vmax with unchanged Km.

Urea cycle rate-limiting enzyme: carbamoyl phosphate synthetase I, activated by N-acetylglutamate.

HMP shunt rate-limiting enzyme: glucose-6-phosphate dehydrogenase, which produces NADPH for reductive biosynthesis and glutathione regeneration.

β-Oxidation cycle products: 1 FADH2, 1 NADH, and 1 acetyl-CoA; carnitine palmitoyltransferase I is the rate-limiting step for mitochondrial fatty acid entry.

Cell cycle checkpoints: G1/S (restriction point, p53), G2/M (DNA damage), and spindle assembly checkpoint during metaphase.

Mitosis order: prophase, metaphase, anaphase, telophase, followed by cytokinesis.

Osmosis moves water across a semipermeable membrane toward higher solute concentration (lower water potential).

Enzymes lower activation energy but do not change ΔG or the equilibrium constant of a reaction.

Na+/K+ ATPase moves 3 Na+ out and 2 K+ in per ATP, contributing to resting membrane potential and cell volume regulation.

Endosymbiotic theory: mitochondria and chloroplasts derive from bacteria, evidenced by circular DNA and 70S ribosomes.

Intrinsic apoptosis: cytochrome c release → apoptosome → caspase-9 → caspase-3.

Logistic growth: dN/dt = rN(1 − N/K); exponential growth: dN/dt = rN.

Gram-positive cell walls have thick peptidoglycan and teichoic acids and stain purple; gram-negative walls have thin peptidoglycan and lipopolysaccharide and stain pink.

Bacterial growth phases: lag, log (exponential), stationary, and death.

Exotoxins are heat-labile proteins, often plasmid-encoded, and can be made into toxoids; endotoxin is heat-stable lipopolysaccharide.

Viral replication: attachment, penetration, uncoating, synthesis, assembly, release; viruses lack ribosomes and require host translation machinery.

Beta-lactams inhibit transpeptidase (cell wall cross-linking); aminoglycosides bind the 30S subunit; macrolides bind the 50S subunit; fluoroquinolones inhibit DNA gyrase.

Autoclave sterilization: 121 °C at 15 psi for about 15 minutes.

Fungal plasma membranes contain ergosterol; azole antifungals inhibit ergosterol synthesis.

Antibiotic-associated colitis is classically caused by Clostridioides difficile overgrowth after disruption of normal colonic flora.

Central dogma: DNA → RNA → protein; transcription uses RNA polymerase, translation uses ribosomes.

Monohybrid cross ratio 3:1; dihybrid cross ratio 9:3:3:1; testcross of a heterozygote gives 1:1.

Hardy–Weinberg: p + q = 1 and p² + 2pq + q² = 1, assuming no mutation, migration, selection, nonrandom mating, or genetic drift.

X-linked recessive: affected males, carrier females, no male-to-male transmission.

Mitochondrial inheritance is maternal, with variable expression due to heteroplasmy.

Frameshift mutations (insertion/deletion not in multiples of three) usually cause more severe protein dysfunction than missense mutations.

Penetrance is the proportion of genotypes expressing a phenotype; expressivity is the degree of phenotypic expression.

Trisomy 21 results from nondisjunction, most often maternal meiosis I, and risk rises with maternal age.

Ideal gas law: PV = nRT; STP molar volume = 22.4 L/mol at 0 °C and 1 atm.

Molarity = moles solute / liters solution; dilution: M1V1 = M2V2.

pH = −log[H+]; pKa = −log Ka; Henderson–Hasselbalch: pH = pKa + log([A−]/[HA]).

Le Chatelier's principle: adding reactant or removing product shifts equilibrium right; increasing pressure favors fewer gas moles; increasing temperature favors the endothermic direction.

ΔG = ΔH − TΔS; ΔG < 0 is spontaneous, ΔG = 0 is equilibrium, ΔG > 0 is nonspontaneous.

First-order half-life t1/2 = 0.693/k and is independent of initial concentration.

Average kinetic energy of gas molecules is proportional to absolute temperature.

Periodic trends: atomic radius decreases left to right across a period and increases down a group; electronegativity increases across and up.

SN2: concerted, backside attack, inversion of configuration, favored by methyl/primary substrates and polar aprotic solvents.

SN1: carbocation intermediate, racemization, favored by tertiary substrates and polar protic solvents.

E2: strong bulky base, anti-periplanar β-hydrogen, concerted; E1 competes with SN1 under protic conditions.

Markovnikov addition of HX to an alkene puts H on the carbon with more hydrogens; HBr with peroxides gives anti-Markovnikov addition.

Hückel aromaticity: cyclic, planar, fully conjugated, 4n + 2 π electrons.

Tollens' reagent oxidizes aldehydes (silver mirror) but not ketones; Grignard reagents add to carbonyls and are destroyed by protic solvents.

Fischer esterification is acid-catalyzed and reversible; saponification is base-promoted hydrolysis of esters.

IR: C=O stretch ~1700 cm−1; broad O–H ~3200–3600 cm−1. 1H NMR: deshielded protons absorb downfield.

Classical conditioning: neutral CS paired with UCS elicits UCR; after learning, CS alone elicits CR; extinction weakens CR, spontaneous recovery may return it.

Operant conditioning: positive reinforcement adds a reward, negative reinforcement removes an aversive stimulus; both increase behavior; punishment decreases behavior.

Reinforcement schedules: fixed ratio produces high rates with post-reinforcement pauses; variable ratio produces high, steady rates resistant to extinction.

Piaget stages: sensorimotor (0–2), preoperational (2–7), concrete operational (7–11), formal operational (11+).

Erikson psychosocial stages include trust vs mistrust (infancy), identity vs role confusion (adolescence), and intimacy vs isolation (young adulthood).

General adaptation syndrome: alarm (sympathetic), resistance (sustained cortisol), exhaustion (resource depletion).

HPA axis: hypothalamus CRH → anterior pituitary ACTH → adrenal cortex cortisol.

Transtheoretical model stages: precontemplation, contemplation, preparation, action, maintenance.