Metabolism and Disposal of Urea, Creatinine and Uric Acid: MCQ

Multiple Choice Question on Metabolism and Disposal of  Urea, Creatinine, 

and Uric Acid

1) The urea molecule consists of two nitrogens and one carbon atom. The first nitrogen atom is derived from the free ammonium ion and the second from an amino acid. The amino acid that donates the  second amino group for the formation of urea is

a) Arginine
b) Aspartate
c) Glutamate
d) Ornithine

2) The free ammonium group  (NH4+) is derived from the following processes:

a) Oxidative deamination of Glutamine catalyzed by enzyme glutamate dehydrogenase
b) Deamidation of histidine catalyzed by the enzyme histidase
c) Deamidation of serine and threonine by a PLP requiring enzyme serine dehydratase
d) All of the above

3) The first step in the urea cycle is a condensation of CO2, ammonia, and ATP to form carbamoyl phosphate. The following are true regarding the formation of carbamoyl phosphate except:

a) The reaction is catalyzed by a rate-limiting enzyme carbamoyl phosphate synthase-I
b) The presence N-acetyl glutamate inhibits the activity of CPS I enzyme
c) Two molecules of ATP are required for this reaction
d) The reaction occurs in mitochondria


4) Which of the following amino acid: keto acid pair bridge the urea cycle with the tricarboxylic acid cycle for the maintenance of nitrogen and amino acid pool

a) Glutamate: Alpha-ketoglutarate
b) Aspartate: Oxaloacetate
c) Alanine: Pyruvate
d) None of the above

5) Four Adenosine triphosphate equivalents are required for the formation of urea in the urea cycle. Which of the following enzymes utilize the ATPs

a) Carbamoyl Phosphate synthase I
b) Ornithine Transcarbamoylase
c) Argininosuccinate synthase
d) Ariginosuccinase

6) The carbamoyl-phosphate is synthesized in the mitochondria and subsequently converted into citrulline. The remainder of the steps occurs in the cytosol requiring the transport of citrulline into the cytosol. The mitochondrial transporter is a

a) symport that co-transport arginine with ornithine
b) antiport that exchange arginine with ornithine
c) symport that co-transport citrulline with ornithine
d) antiport that exchange citrulline with ornithine

7) The deficiency of which of the following enzymes urea cycle results in impaired the synthesis of urea,  accumulation of ammonia (hyperammonemia), and orotic aciduria?

a) Carbamoyl Phosphate synthase I
b) Ornithine Transcarbamoylase
c) Argininosuccinate synthase
d) Ariginosuccinase

8) The deficiency of which of the following enzyme causes Citrullinemia- a condition with an accumulation of citrulline in the blood

a) Carbamoyl Phosphate I
b) Ornithine Transcarbamoylase
c) Argininosuccinate synthase
d) Ariginosuccinase

9) Which of the following compound is administered to the patients with urea cycle defect to remove the ammonia?

a) Inulin
b) Phenylbutyrate
c) Arginine
d) Ornithine


10) The following conditions lead to the hyperammonemia
a) Chronic Liver Cirrhosis
b) GI bleeding
c) Deficiency of CPS I
d) All of the above

11) The creatine synthesis begins in the kidney and is completed liver and require three different amino acid for its formation.  The creatine undergoes phosphorylation to form creatine phosphate in various tissue. The following amino acids are required for its synthesis EXCEPT:

a) Alanine
b) Arginine
c) Glycine
d) Methionine

12) The interconversion of creatine and creatine phosphate is catalyzed by an enzyme creatine kinase. The creatine kinase has three different isoenzymes.  Which of the following isoenzyme is present in heart tissue that is elevated in myocardial infarction?

a) CK-MM
b) CK-MB
c) CK-BB
d) None of the above

13) The interconversion of creatine and creatine phosphate is catalyzed by an enzyme creatine kinase. The creatine kinase has three different isoenzymes.  Which of the following isoenzyme is present in heart tissue that is elevated in skeletal muscle atrophy?

a) CK-MM
b) CK-MB
c) CK-BB
d) None of the above

14) Creatinine is a compound formed by a spontaneous cyclization of creatine phosphate in the brain and muscles. The following statement is true for creatinine EXCEPT:

a) One to two percent of Creatine phosphate is irreversibly converted to creatinine
b) The concentration of creatinine is fairly constant and relative to body muscle mass
c) Creatinine is freely filtered through the glomerular membrane
d) Creatinine is not secreted by kidney tubules


15) Creatinine clearance is used for

a) estimation of renal blood flow
b) estimation of glomerular filtration rate
c) evaluation of nephrolithiasis
d) None of the above

16) Uric acid is the excretory end product of purine metabolism. Which of the following condition lead to the increased production of uric acid

a) Hypoxanthine- Guanosine phosphoribosyltransferase
b) Increased lactate levels and chronic alcoholism
c) Acute and Chronic Renal Disease
d) All of the above

17) Which of the following amino acids have an important role in the transport of amino group from peripheral tissues to the liver?

a) Serine
b) Methionine
c) Glutamine
d) Arginine

18) The following metabolite is excreted via urine to maintain the nitrogen balance except:

a) Amino acids
b) Creatinine
c) Urea
d) Ammonia

19) In citrullinemia- a problem in the urea cycle, which of the following pathway is suppressed?

a) Glycolysis
b) Glycogenesis
c) Glycogenolysis
d) Gluconeogenesis

20) The Urea cycle is the most energy-efficient cycle. It requires ATP for the continuation of the cycle. Identify an intermediate that utilizes ATP for the formation.

a) Arginine
b) Ornithine
c) Citrulline
d) Arginine succinate

21) Which of the following is the end product of purines metabolism in humans?

a) Xanthine
b) Uric acid
c) Urea
d) Allantoin


Multiple Choice Answers
1-b) Aspartate
2-d) All of the above
3- b) The presence N-acetyl glutamate inhibits the activity of CPS I enzyme
4- b) Aspartate: Oxaloacetate
5-a) Carbamoyl Phosphate synthase I &c) Argininosuccinate synthase
6- d) antiport that exchange citrulline with ornithine
7- b) Ornithine Transcarbamoylase
8- c) Argininosuccinate synthase
9- b) Phenylbutyrate
10- d) All of the above
11- a) Alanine
12- b) CK-MB
13- a) CK-MM
14- d) Creatinine is not secreted by kidney tubules
15- b) estimation of glomerular filtration rate
16- d) All of the above
17-c) Glutamine
18-a) Amino acids
19-
d) Gluconeogenesis
20-d) Arginine succinate
21-b) Uric acid



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