Biochemistry Test

Question 1

In order to determine the rate of DNA synthesis in various mammalian tissues, the administration of which of the following labeled substances would be most specific in labeling DNA?

Accepted Answer

Thymidine

Answer

Adenosine

Answer

Cytosine

Answer

Guanosine

Answer

Uridine

Question 2

A 2-year-old boy who recently emigrated from Somalia is brought to the physician because of a 1-day history of pain of his arms and legs. Physical examination shows pale mucous membranes and hepatosplenomegaly. Laboratory studies show a hemoglobin concentration of 8 g/dL. A peripheral blood smear shows sickle cells. Genetic analyses show a point mutation in the β-globin gene leading to a change of a GAG codon (glutamate) to a GUG codon (valine). Which of the following anticodons is most likely in the tRNA for valine?

Accepted Answer

CAC

Answer

CTU

Answer

CUC

Answer

GAC

Answer

GCC

Question 3

Which of the following post-translational modifications is most likely to be found on a cyclin B protein that is targeted for degradation?

Accepted Answer

Ubiquitinated lysine residues

Answer

Acetylated lysine residues

Answer

Phosphorylated serine residues

Answer

Phosphorylated threonine residues

Answer

Phosphorylated tyrosine residues

Question 4

A previously healthy 16-year-old girl is brought to the physician because of abdominal cramps, bloating, and loose stools for 6 months. These symptoms began after she ingested skim milk in an attempt to lose weight. She is at the 50th percentile for height and 75th percentile for weight. Physical examination shows no abnormalities. Stool studies show a 3+ Clinitest reagent response and pH of 5. After the patient ingests milk, there is an increased hydrogen concentration in expired air. A deficiency of which of the following enzyme activities is the most likely cause of the gastrointestinal symptoms in this patient?

Accepted Answer

Lactase

Answer

Amylase

Answer

Carboxypeptidase

Answer

Fructose-1,6-bisphosphate aldolase

Answer

Galactokinase

Answer

Sucrase

Question 5

A married couple is screened to assess the risk for Gaucher disease in their children. The activities of glucocerebrosidase in the sera of the mother and father are 45% and 55%, respectively, of the reference value. The couple has one child. Which of the following is the probability of the child possessing one or more alleles of the Gaucher mutation?

Accepted Answer

0.75

Answer

0

Answer

0.25

Answer

0.5

Answer

1.0

Question 6

The release of epinephrine from the chromaffin granules of the adrenal medulla into the bloodstream in response to neural stimulation is mediated by which of the following?

Accepted Answer

Acetylcholine

Answer

γ-Aminobutyric acid (GABA)

Answer

Cortisol

Answer

Dopamine

Answer

Serotonin

Question 7

During normal screening for phenylketonuria, a male newborn has a serum phenylalanine concentration of 35 mg/dL (greater than 20 mg/dL is considered a positive test). Signs of tyrosine deficiency also are apparent. Enzymatic analysis using cultured fibroblasts, obtained after circumcision, shows normal activity of phenylalanine hydroxylase. A possible explanation for these findings is a deficiency in function of which of the following coenzymes?

Accepted Answer

Biopterin

Answer

Adenosylcobalamin

Answer

Dihydroquinone

Answer

Pyridoxal phosphate

Answer

Tetrahydrofolic acid

Question 8

A 2-year-old boy with mental retardation has chewed the tips of his fingers on both hands and a portion of his lower lip. His serum uric acid concentration is increased, and he has a history of uric acid renal calculi. His 5-year-old brother has similar findings. Which of the following abnormal enzyme activities is the most likely cause of these findings?

Accepted Answer

Decreased hypoxanthine-guanine phosphoribosyltransferase

Answer

Decreased adenine phosphoribosyltransferase

Answer

Decreased adenosine deaminase

Answer

Increased phosphoribosylpyrophosphate synthetase

Answer

Increased xanthine oxidase

Question 9

A 14-year-old girl is brought to the physician because of a recent growth spurt of 15 cm (6 in) during the past year. She also has had increasing fatigue and palpitations during this period. Her paternal aunt has a history of palpitations and severe myopia. She is at the 95th percentile for height and 50th percentile for weight. Physical examination shows a long, thin face. Ophthalmologic examination shows dislocated lenses. Cardiac examination shows a hyperdynamic precordium with early click and systolic murmur. Echocardiography shows an enlarged aortic root and mitral valve prolapse. Abnormal synthesis of which of the following proteins is the most likely cause of this patient’s disorder?

Accepted Answer

Fibrillin-1

Answer

Collagen, type I

Answer

Elastin

Answer

Fibroblast growth factor R3

Answer

Laminin

Answer

Neurofibromin

Answer

PAX 6

Question 10

Native collagen is composed almost entirely of which of the following types of structures?

Accepted Answer

Triple helix

Answer

α-Helix

Answer

β-Pleated sheet

Answer

Random coils

Answer

Two peptides connected by a disulfide bond