Histology NBME Exam Questions with 100% Correct Answers

Cell membrane Correct Answer Phosphatidylcholine and sphingomyelin on EC side Phosphatidylethanolamine and phosphatidylserine on inside Increase in cholesterol = decrease in fluidity/permeability In some cells, covered by carb-rich glycocalyx Receptor-mediated endocytosis = both receptor and ligand get ingested by clathrin-coated vesicle Disorders of transport Correct Answer CF: defect in CTFR = salty sweat and thick mucus Cystinuria: inability to reabsorb cys in kidneys = kidney stones Hereditary hypercholesterolemia: no LDL receptors on cells Textrodotoxin (puffer fish) blocks Na channels = death Disorders of cell signalling Correct Answer Ras: mutation = even on w/o ligand = neoplastic transform Cholera: active GPCR w/o ligand = more cAMP = diarrhea Curare: nACHr antagonist = paralysis Graves: autoimmune stim of TSH receptor = hyperthyroidism and decreased TSH levels Junctions Correct Answer ZO: tight junctions fuse ECM sides of adjacent cell PMs ZO acts a diffusion barrier MA: spot desmosome that has proteins anchored in plaques MA held together by cadherins and leave wide gap b/t cells GJ: connexon channels assoc to form passage b/t cells Mitochrondria Correct Answer Outer membrane is relatively permeable and inner opposite Proteins made from nuclear DNA made in cytosol then imported Lysosomes Correct Answer ATP-powered H pump maintains acidic environment Primary lysosomes bud from Golgi and can't digest Secondary digest and form heterophagic or autophagic vacuole Residual bodies are postdigestive lysosomes with leftover stuff, such as lipofuscin, which increases w/ age Peroxisome Correct Answer Oxidases break down toxic metabolites, releasing H2O2 Catalases break down H2O2 Zellweger = PCKD, jaundice, hypotonia, hepatomegaly