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MCQs on Phenylalanine & Tyrosine Metabolism and Related Disorders: Biochemistry

Multiple Choice Questions on Phenylalanine and Tyrosine Metabolism


1) Tyrosine is a nutritionally non-essential amino acid that is synthesized from tyrosine. 
Identify the enzyme responsible catalyzes the reaction:
a) Tyrosine deaminase 
b) Tyrosinase 
c) Tyrosine Hydroxylase
d) Phenylalanine Hydroxylase 

2) Phenylalanine hydroxylase (PAH) is an enzyme that required the reduced form of which of the following co-factor for its activity?
a) NADH
b) NADPH
c) Reduced Glutathione
d) Reduce tetrahydrobiopterin

3) Phenylketonuria is a genetic disorder caused by a deficiency of an enzyme that converts phenylalanine to tyrosine. 
Identify the correct statements regarding 'phenylketonuria':
a) PKU occurs due to deficiency of both PAH and dihydrobiopterin reductase deficiency
b) Missense mutation of the PAH gene  are frequently observed in PKU patients
c) All PKU patients do not respond to biopterin  treatment
d) None of the above

4) The following are phenyl ketones found in the PKU patients, Except
a) Phenylacetate
b) Phenyl-lactate
c) Phenyl pyruvate
d) Phenyl succinate

5) Which of the following screening assay for PKU is also known as the 'Guthrie test'?
a) Measurement of Phenylalanine level in blood using chromatography
b) Measurement of Phenylalanine level using bacterial inhibition test
c) Detection of Tyrosine level in blood using chromatography
d) Detection of urine phenyl ketones using ferric chloride

6) Tyrosine is the precursor for bioactive hormones and neurotransmitters.
Which of the following bioactive compound is not synthesized from tyrosine?
a) Serotonin
b) Epinephrine
c) Norepinephrine
d) Thyroxine

7) Tyrosinemia-I is a genetic disorder caused by the deficiency of .....................................
a) Fumaryl-Acetoacetate hydrolase 
b) Tyrosine Aminotransferase
c) Hydroxyphenylalainine pyruvate
d) Homogentisate oxidase

8) Tyrosinemia-II is a genetic disorder caused by the deficiency of......................................
a)  Fumaryl-Acetoacetate hydrolase
b) Tyrosine Aminotransferase
c) Hydroxyphenylalainine pyruvate hydroxylase
d) Homogentisate oxidase

9) Alkaptonuria is a genetic disorder caused by the deficiency of which of the following enzyme?
a) Fumaryl-Acetoacetase 
b) Tyrosine Aminotransferase
c) Hydroxyphenylalainine pyruvate hydroxylase
d) Homogentisate oxidase

10) Neonatal Tyrosinemia is a genetic disorder caused by the deficiency of.....................................
a) Fumaryl-Acetoacetase 
b) Tyrosine Aminotransferase
c) Hydroxyphenylalainine pyruvate hydroxylase
d) Homogentisate oxidase

11) Which of the following enzyme require ascorbate (vitamin C) for its activity? 
a) Fumaryl-Acetoacetate hydrolase
b) Tyrosine Aminotransferase
c) Hydroxyphenylalainine pyruvate hydroxylase
d) Homogentisate oxidase

12) The conversion of norepinephrine to epinephrine is catalyzed by phenyl ethanolamine N-methyl transferase. 
Which of the following metabolic intermediate serve as a methyl donor?
a) S-adenosyl cysteine
b) S-adenosyl methionine
c) Alanine 
d) Acetyl CoA  

13) Which of the following is the enzyme required for the synthesis of melanin?
a) Phenylalanine hydroxylase 
b) DOPA decarboxylase
c) Tyrosinase
d) Tyrosine aminotransferase

 14) Which one of the following statements concerning a one-week-old male infant with undetected classic phenylketonuria is correct?
a) Tyrosine is a non-essential amino acid for the infant
b) High levels of phenylpyruvate appear in the urine
c) A diet devoid of phenylalanine should be initiated immediately
d) Therapy must begin within the first year of life.

15) Tyrosinemia Type I is caused by a deficiency of fumarylacetoacetate hydrolase. 
All the following statements are true for this disease, Except
a) Accumulation of Tyrosine in blood
b) Increased methionine
c) Increased succinylacetone
d) Increased Urinary Homogentisate 

16) Which of the following analyte is used for the diagnosis of alkaptonuria?
a) Homogentisate
b) Phenylacetate
c) p-Hyroxyphenylacetate
d) Fumrylacetoacetate


1- d) Phenylalanine Hydroxylase
2-d) Reduce tetrahydrobiopterin
3- Option a & b
4-d) Phenylsuccinate
5-b) Measurement of Phenylalanine level using bacterial inhibition test
6-a) Serotonin
7-a) Fumaryl-Acetoacetase 
8-b) Tyrosine Aminotransferase
9-d) Homogentisate oxidase
10-c) Hydroxyphenylalainine pyruvate hydroxylase
11-c) Hydroxyphenylalainine pyruvate
12-b) S-adenosyl methionine
13-c) Tyrosinase
14-b) High levels of phenylpyruvate appear in the urine
15-d) Increased Urinary Homogentisate 
16-a) Homogentisate

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