Amino Acid Metabolism and Aminoacidurias : MCQ

Glutamate and Glutamine Metabolism

Glutamate and Glutamine are nutritionally non-essential amino acids that are the building block of proteins and, the precursor for the synthesis of other nonessential amino acids, urea, and neurotransmitters. Glutamine also serves as a co-substrate for the formation of asparagine. The glutamate and glutamine synthesis reaction uniquely incorporates free ammonium ions and is important for ammonia metabolism and detoxification.

The metabolic pathway for the synthesis of glutamate and glutamine involves:
 i) Conversion of alpha-ketoglutarate to glutamate by enzyme glutamate dehydrogenase, an NADPH requiring an enzyme that incorporates free ammonia into alpha-keto-glutarate. 
ii) Conversion of glutamate to glutamine is catalyzed by Glutamine synthetase which incorporates ammonium ion and utilizes ATP as energy.

Metabolism of Glutamine and Glutamine 

Fates of Glutamate 

Metabolism of Serine and Glycine

Overview of Glycine and Serine metabolism

Multiple Choice Questions on Amino acid metabolism

1) Glutamate and Glutamine are nutritionally non-essential amino acids. 
The conversion of alpha-ketoglutarate to glutamate and glutamine is catalyzed by:
a) Glutamate synthetase and Glutamate dehydrogenase
b) Glutamate transaminases
c) Glutamate dehydrogenase and Glutamine synthetase
d) None of the Above

2) Which of the following statement is NOT TRUE?
a) Glutamate dehydrogenase catalyzes the incorporation of free ammonium ions to form glutamate
b) Glutamate synthetase utilized ATP as energy for the incorporation of ammonium ions to form glutamine
c) Asparagine synthetase utilized ATP as energy for the incorporation of ammonium ion to form asparagine
d) Asparagine dehydrogenase catalyzes the incorporation of free ammonium ions to form aspartate

3) Glutamate and Glutamine are critical entry points for free ammonia to enter the metabolic pathway. Which of the following pathways glutamate metabolism is regulated by allosteric inhibitors such as alanine, glycine, and carbamoyl phosphate?
a) Glutamate synthase
b) Glutamate synthetase
c) Glutamate dehydrogenase
d) Glutamate deoxygenase

4) N-acetyl Glutamate is an activator of urea synthesis and is formed from condensation glutamate and acetyl CoA. 
Which of the following enzyme catalyzes this reaction?
a) Arginosuccinate synthetase
b) Carbamoyl phosphate synthetase
c) N-Acetyl glutamate synthase
d) Glutaminase

5) Hydroxyproline and hydroxylysine are formed by hydroxylation of proline and lysine; the reaction is catalyzed by prolyl and lysyl hydroxylase. 
Which of the following serve as coenzyme?
a) Biotin
b) Thiamine
c) Ascorbate
d) Niacin

6) Cysteine is a nutritionally non-essential amino acid, and it is synthesized from.............................
a) Proline
b) Valine
c) Glycine
d) Methionine

7) 3-phosphoglycerate is the precursor for all of the following amino acids, EXCEPT
a) Serine
b) Glycine
c) Alanine
d) Cysteine

8) The conversion of serine to glycine is catalyzed by an enzyme serine hydroxymethyltransferase. 
The co-substrate required for this reaction is:
a) Biotin
b) Pyridoxal Phosphate
c) Tetrahydrobiopterin
d) Tetrahydrofolate

9) Alpha-ketoglutarate is the precursor for all the following amino acids, except?
a) Proline
b) Arginine
c) Glutamine
d) Asparagine

10) 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

11) Maple syrup disease is a disorder due to a deficiency of pathway that degrades:
a) Tyrosine
b) Tryptophan
c) Leucine
d) Methionine

12) The phenylalanine metabolism is blocked in the metabolic disease phenylketonuria. 
Which of the following product is formed during the normal metabolism of phenylalanine by phenylalanine hydroxylase?
a) Tyrosine
b) Phenylpyruvate
c) Phenylacetate
d) Phenyl lactate

13) Identify both glucogenic and ketogenic amino acids:
a) Methionine
b) Cysteine
c) Tryptophan
d) Valine

14) Identify the amino acid that participates in methyl group transfer:
a) Leucine
b) Valine
c) Lysine
d) Methionine

15) Which of the following amino acids have an important role in the transport of amino groups from peripheral tissues to the liver?
a) Serine
b) Methionine
c) Glutamine
d) Arginine

16) The following metabolite is excreted via urine to maintain the nitrogen balance, except:
a) Amino acids
b) Creatinine
c) Urea
d) Ammonia

Multiple Choice Answers:
1-c) Glutamate dehydrogenase and Glutamine synthetase
2-d) Asparagine dehydrogenase catalyzes the incorporation free ammonium ion to form aspartate
3-b) Glutamate synthetase
4-c) N-Acetyl glutamate synthase
5-c) Ascorbate
6-d) Methionine
7-b) Glycine
8-c) Tetrahydrobiopterin
9-d) Asparagine
10-b) High levels of phenylpyruvate appear in the urine
11-c) Leucine
12-a) Tyrosine
13-c) Tryptophan
14-d) Methionine
15-c) Glutamine
16-a) Amino acids


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