Download NBME Final- Biochem + Genetics Test Bank 2025 Editions. Real Exam Questions and Answers and more Exams Biochemistry in PDF only on Docsity!
NBME Final- Biochem + Genetics Test Bank
2025 Editions. Real Exam Questions and
Correct Answers. Graded A
22q11 deletion syndromes – ANS Microdeletion at chromosome 22q11 variable presentations including Cleft palate, Abnormal facies, Thymic aplasia T-cell deficiency, Cardiac defects, and Hypocalcemia 2° to parathyroid aplasia. DiGeorge syndrome—thymic, parathyroid, and cardiac defects. Velocardiofacial syndrome—palate, facial, and cardiac defects. CATCH-22. Due to aberrant development of 3rd and 4th branchial pouches. Achondroplasia - ANSMutation of fibroblast growth factor receptor 3 (FGFR3) inhibits chondrocyte proliferation. Most
common cause of dwarfism; limb length affected more than head or torso size. Full penetrance. Actonimyces - ANSanaerobe; normal flora in oral, reproductive, and GI; Causes oral/facial abscesses that drain through sinus tracts, forms yellow "sulfur granules;" can also cause PID with IUDs; treat with penicillin Acute phase reactants - ANSFactors whose serum concentrations change significantly in response to inflammation; produced by the liver in both acute and chronic inflammatory states. Notably induced by IL-6; includes C reactive protein, ferriting, fibrinogen, hepcidin, serum amyloid A Adenosine deaminase deficiency - ANSExcess ATP - prevents DNA synthesis due to (-) feedback -> low lymphocytes Albinism - ANSAutosomal recessive Defective tryosine-3-monooxygenase
silent and Maternal gene is deleted/mutated. Results in inappropriate laughter ("happy puppet"), seizures, ataxia, and severe intellectual disability. 5% of cases due to paternal uniparental disomy (two paternally imprinted genes are received; no maternal gene received). ATP synthase inhibitors - ANSDirectly inhibit mitochondrial ATP synthase, causing an increase proton gradient. No ATP is produced because electron transport stops. Oligomycin. Autosomal Dominant Diseases (that we have covered) - ANSAchondroplasia, familial adenomatous polyposis (FAP), Li-Fraumeni syndrome, Marfan syndrome, NF1, NF2, von Hippel-Lindau Autosomal Dominant Pedigree - ANS Autosomal Recessive Pedigree - ANS
Base Excision Repair - ANSBase-specific glycosylase removes altered base and creates AP site (apurinic/apyrimidinic). One or more nucleotides are removed by AP-endonuclease, which cleaves the 5 end.′ Lyase cleaves the 3 end. DNA polymerase-β′ fills the gap and DNA ligase seals it. Can occur in any phase of cell cycle. Important in repair of spontaneous/toxic deamination. Base excision repair - ANSC-> U (deamination) Uracil DNA glycosylase - cleaves off bases (backbone stays) AP endonuclease - removes backbone New nucleotide added + sealed Becker muscular Dystrophy - ANSX-linked disorder typically due to nonframeshift
Symptoms: failure to thrive, jaundice, hepatomegaly, infantile cataracts, intellectual disability. Can lead to E coli sepsis in neonates. Treatment: exclude galactose and lactose (galactose + glucose) from diet Clostridium difficile - ANSProduces 2 toxins. Toxin A, enterotoxin, binds to the brush border of the gut. Toxin B, cytotoxin, causes cytoskeletal disruption via actin depolymerization > diarrhea
pseudomembranous colitis. Often 2° to antibiotic use, especially clindamycin or ampicillin; associated with PPI use. Diagnosed by detecting one or both toxins in stool by PCR. Difficile causes diarrhea. Treatment: metronidazole or oral vancomycin. For recurrent cases, consider repeating prior regimen, fidaxomicin, or fecal microbiota transplant.
Collagen Types - ANS1 - bone, skin, tendon 2 - cartilage 3 - reticular fibers 4 - basement membrane Complement for neutrophil chemotaxis - ANSC5a Complications associated with CF - ANSRecurrent pulmonary infections (eg, S aureus [early infancy], P aeruginosa [adolescence]), chronic bronchitis and bronchiectasis > reticulonodular pattern on CXR. Pancreatic insufficiency, malabsorption with steatorrhea, fat-soluble vitamin deficiencies (A, D, E, K), biliary cirrhosis, liver disease. Meconium ileus in newborns. Infertility in men (absence of vas deferens, spermatogenesis may be unaffected) and subfertility in women (amenorrhea, abnormally thick cervical mucus). Nasal polyps, clubbing of nails. Composition of collagen - ANStranslation of collagen α chains
retardation, speech delay, heart defect Cri-du-Chat Syndrome - ANSCongenital microdeletion of short arm of chromosome 5 (46,XX or XY, 5p−). Findings: microcephaly, moderate to severe intellectual disability, high-pitched crying/mewing, epicanthal folds, cardiac abnormalities (VSD). Cri du chat = cry of the cat. Cystic Fibrosis - ANSAutosomal recessive CFTR gene - 3 nucleotide deletion (lose Phe) Cl- channel defective - misfolded channel protein gets degraded and lose Cl- secretion Thick mucous in bronchi, GI
Cystic Fibrosis - ANSAutosomal recessive; defect in CFTR gene on chromosome 7; commonly a deletion of Phe508. Most common lethal genetic disease in Caucasian population. CFTR encodes an ATP-gated Cl− channel that secretes Cl− in lungs and GI tract, and reabsorbs Cl− in sweat glands. Most common mutation > misfolded protein > protein retained in RER and not transported to cell membrane, causing decreased Cl− (and H2O) secretion; increased intracellular Cl− results in compensatory increase in Na+ reabsorption via epithelial Na+ channels > increased H2O reabsorption
abnormally thick mucus secreted into lungs and GI tract. Increased Na+ reabsorption also causes more negative transepithelial potential difference. Cytokines secreted by all T cells - ANSIL2 and IL Cytokines secreted by macrophages - ANSIL1, IL6, IL8, IL12, TNF alpha Cytokines secreted by Th2 cells - ANSIL4, IL5, IL
atresia, Hirschsprung disease, congenital heart disease (eg, atrioventricular septal defect), Brushfield spots. Associated with early-onset Alzheimer disease (chromosome 21 codes for amyloid precursor protein) and ^ risk of ALL and AML. 95% of cases due to meiotic nondisjunction (^ with advanced maternal age; from 1:1500 in women < 20 to 1:25 in women > 45 years old). 4% of cases due to unbalanced Robertsonian translocation, most typically between chromosomes 14 and 21. 1% of cases due to mosaicism (no maternal association; postfertilization mitotic error). Incidence 1:700. Drinking age (21). Most common viable chromosomal disorder and most common cause of genetic intellectual disability.
Duchenne Muscular Dystrophy - ANSX-linked disorder typically due to frameshift or nonsense mutations > truncated dystrophin protein > inhibited muscle regeneration. Weakness begins in pelvic girdle muscles and progresses superiorly. Pseudohypertrophy of calf muscles due to fibrofatty replacement of muscle A. Gower maneuver—patients use upper extremities to help them stand up. Waddling gait. Onset before 5 years of age. Dilated cardiomyopathy is common cause of death. Duchenne = deleted dystrophin ^ CK and aldolase are seen; Western blot and muscle biopsy confirm diagnosis. Duchenne muscular dystrophy - ANSX-linked recessive
Edwards Syndrome (trisomy 18) - ANSFindings: severe intellectual disability, rockerbottom feet, micrognathia (small jaw), low-set Ears, clenched hands with overlapping fingers, prominent occiput, congenital heart disease. Death usually occurs within 1 year of birth. Incidence 1:8000. Election age (18). 2nd most common trisomy resulting in live birth (most common is Down syndrome). Effects of bacterial toxins on immune cells - ANSSuperantigens (S pyogenes and S aureus)—cross-link the β region of the T-cell receptor to the MHC class II on APCs. Can activate any CD4+ T cell > massive release of cytokines. Endotoxins/lipopolysaccharide (gram ⊝ bacteria)—directly stimulate macrophages by binding to endotoxin receptor TLR4/CD14; Th cells are not involved. Ehlers Danlos - ANSFaulty collagen synthesis causing
hyperextensible skin, tendency to bleed (easy bruising), and hypermobile joints. Multiple types. Inheritance and severity vary. Can be autosomal dominant or recessive. May be associated with joint dislocation, berry and aortic aneurysms, organ rupture. Hypermobility type (joint instability): most common type. Classical type (joint and skin symptoms): caused by a mutation in type V collagen. Vascular type (vascular and organ rupture): deficient type III collagen. Elastin - ANSStretchy protein in skin, lungs, arteries, vocal cords Marfan syndrome - defective elastin Elastin - ANSStretchy protein within skin, lungs, large arteries, elastic ligaments, vocal cords,
Encapsulated bacteria (that we have covered) - ANSStreptococcus pneumoniae, Escherichia coli, group B Strep Encapsulated bacteria vaccines - ANSPrevnar (PCV, pneumococcal conjugate vaccine), H influenzae B, meningococcal vaccine (conjugate vaccine) Endotoxin - ANSLipid A component of LPS (structural component, released when lysed); outer cell membrane of most G- bacteria; can lead to fever, shock (hypotension); induces TNF, IL1, and IL Enterococci - ANSGram ⊕ cocci. Enterococci (E faecalis and E faecium) are normal colonic flora that are penicillin G resistant and cause UTI, biliary tract infections, and subacute endocarditis (following GI/GU procedures). Catalase ⊝, PYR ⊕, variable hemolysis. VRE (vancomycin-resistant enterococci) are an important cause of nosocomial infection.
Essential Fructosuria - ANSInvolves a defect in fructokinase. Autosomal recessive. A benign, asymptomatic condition, since fructose is not trapped in cells. Symptoms: fructose appears in blood and urine Euk RNA polymerases - ANSRNA pol 1 - rRNA RNA pol 2 - mRNA RNA pol 3 - tRNA Inhibitors - Actinomycin D Familial adenomatous polyposis (FAP) - ANSColon becomes covered with adenomatous polyps after puberty. Progresses to colon cancer unless colon is resected. Mutations on chromosome 5q (APC gene); 5 letters in "polyp." Familial adenomatous polyposis cancer (APC) - ANSAutosomal dominant Colon covered w/ adenomatouss polyps.
