©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED
FIRST PUBLISH OCTOBER 2024
USMLE step 1 – biochemistry Exam Study
Guide Solutions
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)
Page 1/18
, ©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED
FIRST PUBLISH OCTOBER 2024
effect of hyperammonemia on metabolism - ANSWER✔✔-decreased alpha ketoglutarate, inhibiting TCA
cycle
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
Page 2/18
, ©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED
FIRST PUBLISH OCTOBER 2024
tyrosine hydroxylase deficiency
lack of migration of neural crest cells (melanocytes)
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
Page 3/18
FIRST PUBLISH OCTOBER 2024
USMLE step 1 – biochemistry Exam Study
Guide Solutions
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)
Page 1/18
, ©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED
FIRST PUBLISH OCTOBER 2024
effect of hyperammonemia on metabolism - ANSWER✔✔-decreased alpha ketoglutarate, inhibiting TCA
cycle
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
Page 2/18
, ©EMILLECT 2024/2025 ACADEMIC YEAR. ALL RIGHTS RESERVED
FIRST PUBLISH OCTOBER 2024
tyrosine hydroxylase deficiency
lack of migration of neural crest cells (melanocytes)
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
Page 3/18
