Protein Metab MCQ Flashcards
1: Which one of the following observations is NOT consistent with a male patient diagnosed with Hartnup’s disease?
A. The patient has pellagra-like symptoms
B. There is no uptake/absorption of tryptophan, phenylalanine, and other neutral amino acids from the diet
C. The patient exhibits symptoms of hyperaminoacidemia
D. The patient exhibits symptoms of hyperaminoaciduria
E. There is no reabsorption of tryptophan, phenylalanine, and other neutral amino acids in the kidneys
C. The patient exhibits symptoms of hyperaminoacidemia
- Which clinical laboratory observation below is suggestive of Hartnup disease (neutral amino acid transport deficiency)?
a. Burnt-sugar smell in urine
b. High plasma phenylalanine levels
c. Extremely high levels of citrulline in urine
d. Elevation of glutamine in blood and urine
e. Elevated plasma tyrosine and methionine levels
f. Dark urine
g. High fecal levels of tryptophan and indole derivatives
g. High fecal levels of tryptophan and indole derivatives
MIGHT be possible, but high urine levels are more likely. levels will be higher than a normal person’s, bc Hartnup patients can’t absorb Trp at the intestinal brush border, but fecal Trp won’t skyrocket – it just represents 100% of the unabsorbed Trp. There is a HIGH concentration in the urine because it gets filtered out from the blood though; the renal tubules can’t reabsorb Trp (and other neutral AA) that gets filtered out
C: not exactly diagnostic of Hartnup, but this is broadly indicative of an AA disorder. Can also be citrullnaemia type I, arginiosuccinic aciduria, citrin deficiency, pyruvate carboxylate deficiency… (according to KK Hospital’s website)
- Which of the following is true about nitrogen (protein) balance?
a. it is positive during trauma or metabolic stress
b. urine nitrogen loss increases during prolonged fast
c. positive during normal childhood
d. negative when taking high protein diet
e. increasing fat metabolism decreases urine nitrogen loss
b. urine nitrogen loss increases during prolonged fast
c. positive during normal childhood
- Enzyme X catalyses the oxidation as well as the deamination of an amino acid Y with the help of the coenzyme NAD+. The resultant product can be transaminated with another amino acid to resynthesise Y. Which of the following enzymes is X?
a. L-amino acid oxidase
b. Glutamate dehydrogenase
c. Serine dehydratase
d. Alanine aminotransferase
b. Glutamate dehydrogenase
- Liver aminotransferases, which are also called transaminases, catalyze the transfer of α-amino groups from many different amino acids to α-ketoglutarate. The intermediate produced is deaminated back to α-ketoglutarate with the formation of ammonium ion. What is the intermediate produced?
a. Aspartate
b. Alanine
c. Oxaloacetate
d. Glutamate
e. Pyruvate
d. Glutamate
1. A patient presents with hyperammonemia (3 times the normal body concentration of ammonia., upon taking history, the doctor found out the patient had eaten unknown wild berries from a tropical country and believes that a chemical in the berries REVERSIBLY INHIBITED an enzyme in the urea cycle that led to this presentation. Which enzyme is this likely to be? A. Carbamoyl Phosphate Synthetase I B. Carbamoyl Phosphate Synthetase II C. Ornithine Transcarbamoylase D. Argininosuccinate Synthase E. Argininosuccinate Lyase
A. Carbamoyl Phosphate Synthetase I
- The disease argininosuccinicemia
A. Is caused by deficiency in argininosuccinate lyase
B. Is caused by deficiency in argininosuccinate synthetase
C. Results in excess urea & a.a. excretion
D. Is caused by deficiency in arginase
E. Is caused by deficiency in Ornithine transcarbamoylase
A. Is caused by deficiency in argininosuccinate lyase
- Which of the following about the urea cycle is correct?
a) last reaction occurs in mitochondria
b) same transport protein for citrulline and ornithine across the inner mitochondrial membrane
c) malate is an intermediate product
d) arginosuccinate synthetase catalyzes condensation of ornithine and aspartate
e) it requires the hydrolysis of 2 ATP per urea molecule
b) same transport protein for citrulline and ornithine across the inner mitochondrial membrane
note: urea cycle requires 3ATP per urea molecule (2ATP in formation of carbomyl phosphate and 1ATP when adding aspartate to citrulline)
- In the urea cycle, which compound is derived from a condensation of CO2 and NH4+?
a. Compound A (citrulline)
b. Compound B (arginine)
c. Compound C (urea)
d. Compound D (argininosuccinate lyase)
e. Compound E (carbamoyl phosphate)
e. Compound E (carbamoyl phosphate)
- In the urea cycle, which compound is considered the end product?
a. Compound A (citrulline)
b. Compound B (arginine)
c. Compound C (urea)
d. Compound D (argininosuccinate lyase)
e. Compound E (carbamoyl phosphate)
c. Compound C (urea)
- The reactions of the urea cycle occur
a. In the cytosol
b. In the mitochondrial matrix
c. In the mitochondrial matrix and the cytosol
d. Only in lysosomes
e. In peroxisomes
c. In the mitochondrial matrix and the cytosol
- A newborn becomes progressively lethargic after feeding and increases his respiratory rate. He becomes virtually comatose, responding only to painful stimuli, and exhibits mild respiratory alkalosis. Suspicion of a urea cycle disorder is aroused and evaluation of serum amino acid levels is initiated. In the presence of hyperammonemia, production of which of the following amino acids is always increased?
a. Glycine
b. Arginine
c. Proline
d. Histidine
e. Glutamine
e. Glutamine
- Which of the following amino acids is a precursor to cysteine?
a. Threonine
b. Methionine
c. Glutamine
d. Lysine
e. Alanine
b. Methionine
- A deficiency in tetrahydrobiopterin results in symptoms associated with phenylketonuria because it is required for:
A. the hydroxylation of phenylalanine
B. the degradation of tyrosine
C. the methylation of dopamine
D. the transfer of two-carbon units
E. the conversion of methionine to cysteine
A. the hydroxylation of phenylalanine
2. In a patient suffering from alcaptonuria, which of the following will accumulate? A. Mannitol B. Melatonin C. Homogentisate D. Acetoacetate
C. Homogentisate
Alcaptonuria arises due to a defect in homogentisate oxidase, which catalyses the conversion of homogentisate to 4-Maleylacetoacetate. Hence, an enzymatic defect will result in the accumulation of the substrate (homogentisate).
