Biochemistry for the USMLE Step 1 Emma Holliday Ramahi ...

Biochemistry for the USMLE Step 1
Emma Holliday Ramahi- Sponsored by the UTHSCSA Office of Academic Enhancement
1.) A woman brings her 3 year old daughter to see the pediatrician because of pallor and failure to gain
weight and meet appropriate developmental milestones. Hemoglobin and hematocrit were found to be
7/21. MCV was found to be 105. B12 and folate administration did not improve the anemia. Ammonia
levels were found to be normal, but excess orotic acid was found in her urine.
Which of the following enzymes is likely in this child
A- orotidine 5’-phosphate decarboxylase deficiency
B- ornithine transcarbamoylase deficiency
C- ribonucleoside reductase
D- thymidylate synthase
E- dihydrofolate reductase
F- xanthine oxidase
G- hypoxanthine-guanine phosphoribosyl transferase
2.) A young mother (#8 in the pedigree) visits with a geneticist before she and her husband conceive a
baby because a she says a “disease runs in her family”. Not shown in the pedigree, but her cousins
(three daughters of #3) are also affeted. Which of the following could be symptoms of this disease
A- Pelvic girdle muscle weakness & cardiomyopathy
B- Growth retardation, failure to walk and widened joint spaces
C- Failure to thrive, meconium ileus, recurrent pseudomonas infections
D- Myoclonic epilepsy, exercise intolerance and lactic acidosis
E- Microcephaly, high pitched cry, cardiac abnormalities
3.) An 18 y/o member of the high school football team presents for his annual sports physical. His
physician notes an erythematous scaly rash on his extremities, hair loss and redness of the conjunctiva.
On further questioning, he reports drinking a homemade energy drink every morning consisting of
orange juice, bananas, 8 raw eggs and whey protein powder.
Which of the following enzymes requires the deficient vitamin as a co-factor
A- proline hydroxylase
B- homocysteine methyltransferase
C- transketolase
D- transaminase
E- acyl-CoA dehydrogenase
F- pyruvate dehydrogenase
G- pyruvate carboxylase
H- gamma glutamyl carboxylase

4.) A post-doctorate student is studying the enzyme-catalyzed steps of glycolysis in mouse skeletal
muscle tissue. He has isolated an enzyme catalyzing an irreversible step that is allosterically inhibited by
glucose-6-phosphate. Which of the following is true of the isolated enzyme
A- it has a high Km
B- it has a high affinity for its substrate
C- it has a high Vmax
D- it is induced by hyperinsulinemia
E- it is inhibited by glucagon and epinephrine
F- it catalyzes the rate limiting step of glycolysis
G- its deficiency is the 2 nd leading cause of hemolytic anemia
5.) A 33 year old woman is brought into the ER by her husband after being found unconscious in the
garage. She has been depressed lately and her husband suspects a suicide attempt via rat poison
ingestion. The emergency room physician notes a strong garlic aroma coming from the patient.
Which of the following will be increased
A- Rate of Gluconeogenesis
B- Rate of Oxidative phosphorylation
C- O 2 consumption
D- H 2 O 2 production
E- Concentration of NADH
F- Concentration of citrate
6.) A 6 year old girl with short stature, ataxia, cardiac conduction defects and pigmentary retinopathy is
diagnosed with Kearns-Sayre syndrome. Genetic analysis reveals a mutation rendering complex II of the
electron transport chain completely non-functional. The electrons initially derived from which Kreb’s
cycle substrate would be unable to be utilized in the synthesis of ATP
A- Pyruvate
B- Citrate
C- Isocitrate
D- α-ketoglutarate
E- Succinyl Co-A
F- Succinate
G- Fumarate
H- Malate

7.) A 24 month old boy is brought into the emergency room the day after his 2nd birthday party after
multiple episodes of vomiting. The child is now lethargic and will not respond to his mother. At the
party, his mother served chocolate cake, ice-cream and Big Red. His mother reports episodes of nausea
and vomiting after “too many sweets” in the past, but never this bad. A blood glucose reading in the ER
reports 35mg/dL. What is most likely elevated in this boy’s serum
A- Galactose
B- Galactose 1-phosphate
C- Fructose
D- Fructose 1-phosphate
E- Lactose
F- Glucose 6-phosphate
G- Long chain fatty acids
H- Dicarboxylic acids
8.) A 3 year old child with light blond hair is brought to the pediatrician by her parents because of
mental retardation. She is found to be tall for her age, with long limbs the following finding on physical
exam bilaterally:
What substance is most likely to be elevated
A- Tyrosine
B- Cysteine
C- Methionine
D- Galactose
E- Fructose
F- Leucine
G- Phenylalanine
H- Tryptophan

9.) A mother brings in her adopted 3 year old son to the pediatrician because he refuses to bear weight
on his right leg and cries when the doctor palpates his right hip joint. The doctor also notes a fullness in
both the right and left upper quadrants on palpation. The child has reached all his developmental
milestones so far, but his family history is unknown.
Concerned for a septic joint, the doctor obtains a pathologic specimen from the bone which is shown
below. What substrate is indicated by the arrow
A- ceramide trihexoside
B- glucocerebroside
C- galactocerebroside
D- sphingomyelin
E- GM2 ganglioside
F- cerebroside sulfate
G- proteoglycans
H- glycoproteins
10.) A 12 y/o boy presents w/ a 24 hour history of nausea, vomiting and 10/10 sharp midepigastric pain
that radiates straight through to his back. When the tech draws blood for labs, she notes it to be milky in
color.
The following laboratory values are obtained:
AST- 80 ALT- 75 Tbili- 1.5 albumin- 4.0
Amylase- 500 Lipase- 690
LDL- 55 HDL- 75 TG- 2500
Which of the following is most likely decreased
A- lipoprotein lipase
B- LDL receptors
C- B-100 and B-48
D- Lecithin Cholesterol Acyltransferase
E- C-II
F- none of the above