©SOPHIABENNET@2024/2025 Tuesday, August 20, 202410:21 AM
USMLE step 1 – biochemistry Practice
Questions and Answers (100% Pass)
infant with somnolence, vomiting, cerebral edema, decreased BUN,
hyperammonemia - Answer✔️✔️-ornithine transcarbamoylase
deficiency
infantile cataracts, doesn't track objects, absent social smile -
Answer✔️✔️-galactokinase deficiency
infantile cataracts, hepatomegaly, jaundice, failure to thrive -
Answer✔️✔️-uridyltransferase deficiency
causes of Down syndrome - Answer✔️✔️-1) meiotic nondisjunction
(95%)
2) unbalanced robertsonian translocation (extra arm on Ch 21)
3) mosaic trisomy 21
treatment of hyperammonemia (HCV, urea cycle deficiency) -
Answer✔️✔️-limit protein in diet
benzoate, phenylbutarate (bind a.a.'s, increased aa exretion)
actulose (acidify GI tract, trap NH4 for excretion)
effect of hyperammonemia on metabolism - Answer✔️✔️-decreased
alpha ketoglutarate, inhibiting TCA cycle
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, ©SOPHIABENNET@2024/2025 Tuesday, August 20, 202410:21 AM
Tay-Sach's (enzyme, accumulated substance) - Answer✔️✔️-
hexosaminidase, GM2 ganglioside
metachromatic leukodystrophy (enzyme, accumulated substance) -
Answer✔️✔️-arylsulfatase, cerebroside sulfate
fabry's (enzyme, accumulated substance) - Answer✔️✔️-alpha-
galactosidase, ceramide trihexoside
krabbe's (enzyme, accumulated substance) - Answer✔️✔️-beta-
galactocerebrosidase, galactocerebroside
gauche's (enzyme, accumulated substance) - Answer✔️✔️-
glucocerebrosidase, glucocerebroside
niemann-pick - Answer✔️✔️-sphingomyelinase, sphingomyelin
hepatosplenomegaly, aseptic necrosis of femur, bone crises,
macrophages that look like crumpled tissue paper - Answer✔️✔️-
Gaucher's sphingolipidosis (glucocerebroside accumulation)
cherry macula, neurodegeneration, foam cells, hepatomegaly -
Answer✔️✔️-niemann-pick (sphyngomyelin)
cherry macula, neurodegenration, lysosomes with onion skin, NO
hepatisplenomegaly - Answer✔️✔️-tay-sachs (GM2 ganglioside)
causes of albinism - Answer✔️✔️-tyrosine transporter defect
tyrosine hydroxylase deficiency
lack of migration of neural crest cells (melanocytes)
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, ©SOPHIABENNET@2024/2025 Tuesday, August 20, 202410:21 AM
where do preganglionic parasympathetic neurons originate? -
Answer✔️✔️-nuclei of cranial nerves
sacral spinal cord (S2-S4)
where do preganglionic sympathetic neurons originate? -
Answer✔️✔️-thoracolumbar spinal cord (T1-L3)
arginine derivatives - Answer✔️✔️-creatine
urea (urea cycle intermediate)
NO
glutamate derivatives - Answer✔️✔️-GABA
glutathione
snRNPs - Answer✔️✔️-combine with pre-mRNA in nucleus to form
spliceosome to remove introns
what must happen in the nucleus so that 7-methylguanosine can
be added to RNA in the cytosol? - Answer✔️✔️-5' capping
what is the purpose of the mRNA 3' poly-A tail? - Answer✔️✔️-export
of mRNA from the nucleus
protection from enzymatic degradation in the cytoplasm
infant with coarse facial features, clouded corneas, restricted joint
movement - Answer✔️✔️-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
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