USMLE step 1 - biochemistry Questions and Answers well Explained Latest 2024/2025 Update 100% Correct.

what must happen in the nucleus so that 7-methylguanosine can be added to RNA in the cytosol? - 5' capping treatment of hyperammonemia (HCV, urea cycle deficiency) - limit protein in diet benzoate, phenylbutarate (bind a.a.'s, increased aa exretion) actulose (acidify GI tract, trap NH4 for excretion) infant with somnolence, vomiting, cerebral edema, decreased BUN, hyperammonemia - ornithine transcarbamoylase deficiency infantile cataracts, doesn't track objects, absent social smile - galactokinase deficiency infantile cataracts, hepatomegaly, jaundice, failure to thrive - uridyltransferase deficiency causes of Down syndrome - 1) meiotic nondisjunction (95%) 2) unbalanced robertsonian translocation (extra arm on Ch 21) 3) mosaic trisomy 21 effect of hyperammonemia on metabolism - decreased alpha ketoglutarate, inhibiting TCA cycle Tay-Sach's (enzyme, accumulated substance) - hexosaminidase, GM2 ganglioside metachromatic leukodystrophy (enzyme, accumulated substance) - arylsulfatase, cerebroside sulfate fabry's (enzyme, accumulated substance) - alpha-galactosidase, ceramide trihexosidekrabbe's (enzyme, accumulated substance) - beta-galactocerebrosidase, galactocerebroside gauche's (enzyme, accumulated substance) - glucocerebrosidase, glucocerebroside niemann-pick - sphingomyelinase, sphingomyelin hepatosplenomegaly, aseptic necrosis of femur, bone crises, macrophages that look like crumpled tissue paper - Gaucher's sphingolipidosis (glucocerebroside accumulation) cherry macula, neurodegeneration, foam cells, hepatomegaly - niemann-pick (sphyngomyelin) cherry macula, neurodegenration, lysosomes with onion skin, NO hepatisplenomegaly - tay-sachs (GM2 ganglioside) causes of albinism - tyrosine transporter defect tyrosine hydroxylase deficiency lack of migration of neural crest cells (melanocytes) where do preganglionic parasympathetic neurons originate? - nuclei of cranial nerves sacral spinal cord (S2-S4) where do preganglionic sympathetic neurons originate? - thoracolumbar spinal cord (T1-L3) arginine derivatives - creatine urea (urea cycle intermediate) NO glutamate derivatives - GABA glutathionesnRNPs - combine with pre-mRNA in nucleus to form spliceosome to remove introns what is the purpose of the mRNA 3' poly-A tail? - export of mRNA from the nucleus protection from enzymatic degradation in the cytoplasm infant with coarse facial features, clouded corneas, restricted joint movement - I cell disease: failure of mannose phosphorylation of lysosome proteins in cis golgi -- lysosomal enzymes are secreted outside the cell instead of sent to lysosome mitochondrial DNA structure - double stranded circular ligand-gated ion channels - GABA (Cl-) glutamate (NMDA/Ca), AMPA/Na) Ach at NMJ (Nm/Na, K) receptor that, when activated, causes renal vasodilation - D1 autonomic receptor that causes vasoconstriction - alpha-1 autonomic receptor that causes vasodilation - beta-2, M3