NBE Sciences cheat sheet

Cell theory: all living organisms are composed of one or more cells; the cell is the basic unit of life; new cells arise from pre-existing cells via division.

Prokaryotes lack a membrane-bound nucleus and organelles; eukaryotes have a nucleus and membrane-bound organelles (mitochondria, ER, Golgi).

DNA replication is semiconservative: each new double helix contains one parental strand and one newly synthesized strand; occurs in S phase.

Transcription converts DNA to mRNA in the nucleus; translation occurs on ribosomes in the cytoplasm, using tRNA to add amino acids in codon-specified order.

Mitosis produces two genetically identical diploid daughter cells (prophase, metaphase, anaphase, telophase); meiosis produces four haploid gametes with crossing over in prophase I.

Mendelian genetics: alleles segregate independently; dominant allele masks recessive; genotype determines phenotype; Punnett square predicts offspring ratios.

Enzymes are biological catalysts that lower activation energy; activity is affected by pH, temperature, substrate concentration, and inhibitors (competitive vs. noncompetitive).

Cellular respiration: glycolysis (cytoplasm) yields 2 ATP and 2 pyruvate; Krebs cycle and oxidative phosphorylation (mitochondria) yield most ATP via electron transport chain.

Photosynthesis: light-dependent reactions in thylakoid membranes produce ATP and NADPH; Calvin cycle in stroma fixes CO2 into glucose using RuBisCO.

Atomic number (Z) = number of protons; mass number (A) = protons + neutrons; isotopes have same Z but different A.

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

Ideal gas law: PV = nRT; R = 0.08206 L·atm/(mol·K); STP = 0°C (273.15 K) and 1 atm, molar volume = 22.4 L/mol.

Molarity (M) = moles solute / liters solution; dilution: M1V1 = M2V2; pH = -log[H+]; pOH = -log[OH-]; pH + pOH = 14 at 25°C.

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

Acid-base: strong acids/bases dissociate completely; weak acids partially ionize (Ka); buffer resists pH change when [A-]/[HA] ratio is near 1 (Henderson-Hasselbalch: pH = pKa + log([A-]/[HA])).

Oxidation = loss of electrons (increase in oxidation number); reduction = gain of electrons; oxidizing agent is reduced, reducing agent is oxidized.

Thermochemistry: ΔH < 0 exothermic; ΔG = ΔH - TΔS; spontaneous when ΔG < 0; entropy (ΔS) generally increases with more gas moles or disorder.

Colligative properties depend on number of solute particles: boiling point elevation (ΔTb = i·Kb·m), freezing point depression (ΔTf = i·Kf·m), osmotic pressure (π = iMRT).

IUPAC naming: longest carbon chain determines parent name; number from end giving lowest locants to substituents; prefix substituents alphabetically.

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

Hybridization: sp3 (tetrahedral, 109.5°), sp2 (trigonal planar, 120°), sp (linear, 180°); double bond = one sigma + one pi; triple bond = one sigma + two pi.

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

Elimination: E1 competes with SN1 (carbocation intermediate); E2 is concerted, requires anti-periplanar geometry, favored by strong bulky base and heat.

Aromaticity (Hückel): cyclic, planar, fully conjugated, 4n+2 π electrons; benzene (6 π e-) is aromatic; cyclobutadiene (4 π e-) is antiaromatic.

Electrophilic aromatic substitution: activating groups (–OH, –NH2, –OR, alkyl) direct ortho/para; deactivating groups (–NO2, –CN, –SO3H, carbonyl) direct meta; halogens are deactivating but ortho/para directing.

Alcohol reactions: oxidation to aldehyde (primary, mild oxidant) or carboxylic acid (strong oxidant); secondary to ketone; tertiary alcohols resist oxidation; dehydration with acid/heat yields alkene.

Carbonyl chemistry: aldehydes are more reactive than ketones toward nucleophilic addition; carboxylic acid derivatives reactivity: acid chloride > anhydride > ester > amide.

Newton's laws: F = ma (net force); inertia (first law); action-reaction pairs act on different bodies (third law).

Kinematics: v = v0 + at; x = v0t + ½at²; v² = v0² + 2ax (constant acceleration only).

Work-energy: W = Fd cosθ; kinetic energy KE = ½mv²; gravitational potential energy PE = mgh; conservation of mechanical energy when only conservative forces act.

Momentum: p = mv; impulse J = FΔt = Δp; in isolated system total momentum is conserved (elastic: KE conserved; inelastic: KE not conserved).

Circular motion: centripetal acceleration a = v²/r; centripetal force Fc = mv²/r directed toward center.

Ohm's law: V = IR; power P = IV = I²R = V²/R; resistors in series add (Req = R1+R2+...); in parallel 1/Req = 1/R1 + 1/R2 + ...

Waves: speed v = fλ; sound intensity level β(dB) = 10 log(I/I0), I0 = 10⁻¹² W/m²; Doppler shift increases frequency when source approaches observer.

Optics: Snell's law n1 sinθ1 = n2 sinθ2; total internal reflection when angle exceeds critical angle θc = sin⁻¹(n2/n1) for n1 > n2; thin lens equation 1/f = 1/do + 1/di.

Thermodynamics: first law ΔU = Q - W; efficiency of heat engine e = W/QH = 1 - QC/QH; Carnot efficiency e_max = 1 - TC/TH (Kelvin).

Anatomical position: standing erect, face forward, arms at sides with palms forward; terms: anterior/ventral, posterior/dorsal, superior/cranial, inferior/caudal, medial, lateral, proximal, distal.

Body planes: sagittal divides left/right; coronal (frontal) divides anterior/posterior; transverse (horizontal) divides superior/inferior.

Skeletal system: 206 bones in adult; axial skeleton (skull, vertebral column, rib cage) and appendicular skeleton (limbs, girdles); functions: support, protection, movement, mineral storage, blood cell production.

Bone tissue: compact (dense) and spongy (cancellous); osteons are structural units; osteoblasts build bone, osteoclasts resorb bone, osteocytes maintain matrix.

Muscular system: skeletal (voluntary, striated), cardiac (involuntary, striated, intercalated discs), smooth (involuntary, non-striated); origin = fixed attachment, insertion = movable attachment.

Major muscles: masseter elevates mandible; temporalis elevates and retracts mandible; sternocleidomastoid flexes and rotates head; diaphragm primary muscle of inspiration; biceps brachii flexes elbow; triceps brachii extends elbow.

Digestive tract order: oral cavity → pharynx → esophagus → stomach → small intestine (duodenum, jejunum, ileum) → large intestine → rectum → anus; accessory organs: liver, gallbladder, pancreas, salivary glands.

Respiratory system: upper (nose, pharynx, larynx) and lower (trachea, bronchi, bronchioles, alveoli); gas exchange occurs in alveoli; right lung has three lobes, left has two.

Cardiovascular: heart has four chambers (right atrium, right ventricle, left atrium, left ventricle); valves: tricuspid (right AV), pulmonary semilunar, mitral (left AV), aortic semilunar; systemic circulation left ventricle → aorta → body → vena cava → right atrium.

Resting membrane potential ≈ -70 mV (inside negative); maintained by Na+/K+ ATPase (3 Na+ out, 2 K+ in) and selective permeability (more K+ leak channels).

Action potential phases: depolarization (Na+ influx), repolarization (K+ efflux), hyperpolarization; threshold ≈ -55 mV; refractory periods prevent backward propagation.

Synaptic transmission: Ca2+ influx triggers neurotransmitter vesicle fusion; neurotransmitter binds postsynaptic receptors; removal by reuptake, enzymatic degradation, or diffusion.

Cardiac cycle: systole (ventricular contraction, ejection) and diastole (ventricular relaxation, filling); normal heart rate 60–100 bpm; cardiac output = heart rate × stroke volume (≈5 L/min at rest).

Blood pressure: systolic/diastolic (120/80 mmHg typical); regulated by baroreceptors, renin-angiotensin-aldosterone system, and sympathetic/parasympathetic tone.

Respiratory physiology: tidal volume ≈500 mL; vital capacity = maximal expiration after maximal inspiration; gas exchange by diffusion driven by partial pressure gradients (PO2 alveolar > blood; PCO2 blood > alveolar).

Renal physiology: nephron functional unit; glomerular filtration → tubular reabsorption (glucose, amino acids, most water) → tubular secretion → excretion; ADH increases water reabsorption; aldosterone increases Na+ reabsorption.

Endocrine: insulin lowers blood glucose (promotes uptake and storage); glucagon raises blood glucose; thyroid hormones regulate metabolic rate; cortisol is a glucocorticoid involved in stress response.

Homeostasis: negative feedback loops maintain internal stability (e.g., body temperature, blood glucose); positive feedback amplifies change (e.g., oxytocin during childbirth).

Cell injury: reversible (cellular swelling, fatty change) vs. irreversible (nuclear dissolution, membrane rupture); causes include hypoxia, ischemia, toxins, infection, immune reactions, genetic defects.

Necrosis types: coagulative (ischemia, protein denaturation), liquefactive (brain infarct, abscess), caseous (tuberculosis), fat necrosis (pancreatitis), fibrinoid (vasculitis).

Apoptosis: programmed cell death, energy-dependent, no inflammation; mediated by caspases; intrinsic (mitochondrial cytochrome c) and extrinsic (death receptor) pathways.

Inflammation: acute response (vasodilation, increased permeability, neutrophil infiltration) vs. chronic (lymphocytes, macrophages, fibrosis); cardinal signs: redness, heat, swelling, pain, loss of function.

Neoplasia: benign vs. malignant; malignant features include invasion, metastasis, anaplasia, high mitotic rate; carcinoma arises from epithelium, sarcoma from mesenchyme; grading (differentiation) vs. staging (spread).

Thrombosis: Virchow's triad = endothelial injury, stasis/turbulence, hypercoagulability; thrombus vs. embolus (traveling clot); infarction = ischemic necrosis.

Atherosclerosis: plaque formation in large/medium arteries; risk factors include hypertension, hyperlipidemia, smoking, diabetes; complications: ulceration, thrombosis, aneurysm.

Cell cycle checkpoints: G1/S (restriction point), G2/M; tumor suppressor genes (p53, RB) inhibit proliferation; oncogenes (RAS, MYC) promote proliferation; two-hit hypothesis for tumor suppressors.

Healing: primary intention (clean wound edges) vs. secondary intention (large tissue loss, granulation); factors impairing healing: infection, poor blood supply, diabetes, malnutrition, steroids.

Bacterial classification: Gram-positive (thick peptidoglycan, purple) vs. Gram-negative (thin peptidoglycan, outer membrane, pink); shape: cocci, bacilli, spirilla.

Bacterial growth curve: lag phase (adaptation), log phase (exponential growth), stationary phase (growth rate = death rate), death phase; generation time varies by species.

Sterilization vs. disinfection: sterilization kills all microorganisms including spores; disinfection reduces pathogens on inanimate objects; antiseptics used on living tissue.

Antibiotic mechanisms: cell wall synthesis inhibitors (penicillins, cephalosporins), protein synthesis inhibitors (aminoglycosides, tetracyclines, macrolides), nucleic acid inhibitors (fluoroquinolones), folate synthesis inhibitors (sulfonamides).

Viruses: obligate intracellular parasites; capsid + nucleic acid (DNA or RNA); replication steps: attachment, penetration, uncoating, biosynthesis, assembly, release; not affected by antibiotics.

Fungi: eukaryotic; yeasts (unicellular) and molds (multicellular hyphae); antifungal targets: ergosterol synthesis (azoles), cell wall (echinocandins), nucleic acid (flucytosine).

Normal flora: resident microorganisms on skin and mucous membranes; provide colonization resistance; opportunistic infections when host defenses are compromised.

Nosocomial infections: acquired in healthcare settings; common pathogens include MRSA, C. difficile, Pseudomonas aeruginosa, E. coli; prevention via hand hygiene and sterilization.

Immunity: innate (nonspecific, immediate: barriers, phagocytes, inflammation) vs. adaptive (specific, memory: B cells/antibodies, T cells); active immunity (vaccination/infection) vs. passive (maternal antibodies, immunoglobulin).

Dental amalgam: alloy of silver, tin, copper, mercury; sets by amalgamation; advantages: strength, durability, low cost; disadvantages: esthetics, mercury toxicity concerns, no adhesive bonding.

Composite resins: resin matrix (BIS-GMA, UDMA) + filler particles (silica, glass); light-cured; advantages: esthetics, adhesive bonding; disadvantages: polymerization shrinkage, wear, technique sensitivity.

Glass ionomer cement: powder (glass) + liquid (polyacrylic acid); releases fluoride; chemical adhesion to tooth structure; uses: liners, bases, luting, pediatric restorations; lower strength than composites.

Zinc oxide-eugenol (ZOE): obtundent effect on pulp; used as temporary filling and base; eugenol is toxic to pulp in deep cavities; reinforced ZOE (IRM) for temporary restorations.

Dental ceramics: porcelain (feldspathic), lithium disilicate, zirconia; high esthetics and wear resistance; brittle, may require metal or zirconia substructure; etching with HF for bonding.

Dental cements: zinc phosphate (mechanical retention, acidic), polycarboxylate (adheres to tooth and metal), resin-modified glass ionomer (dual-cure, fluoride release).

Impression materials: alginate (irreversible hydrocolloid, fast, dimensionally unstable), elastomers (polyvinyl siloxane, polyether; accurate, stable), compound (thermoplastic, used for border molding).

Dental casting alloys: high noble (Au ≥40%, Au+PGM ≥60%), noble (Au+PGM ≥25%), base metal (Ni-Cr, Co-Cr); porcelain-fused-to-metal requires matching coefficient of thermal expansion.

Biocompatibility: materials must not elicit adverse local or systemic responses; test for cytotoxicity, sensitization, irritation; polymerization shrinkage can cause marginal leakage and secondary caries.