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Section VI – Metabolism of Proteins & Amino Acids

Select the one of the following statements that is NOT CORRECT:

A. Δ1-Pyrroline-5-carboxylate is an intermediate both in the biosynthesis and in the catabolism of L-proline.

B. Human tissues can form dietarily nonessential amino acids from amphibolic intermediates or from dietarily essential amino acids.

C. Human liver tissue can form serine from the glycolytic intermediate 3-phosphoglycerate.

D. The reaction catalyzed by phenylalanine hydroxylase interconverts phenylalanine and tyrosine.

E. The reducing power of tetrahydrobiopterin derives ultimately from NADPH.

Phenylalanine hydroxylase catalyzes a functionally irreversible reaction, and thus cannot convert tyrosine to phenylalanine.

Identify the metabolite that does NOT serve as a precursor of a dietarily essential amino acid:

A. α-Ketoglutarate

B. 3-Phosphoglycerate

C. Glutamate

D. Aspartate

E. Histamine

Histamine is a catabolite, not a precursor, of histidine.

Select the one of the following statements that is NOT CORRECT:

A. Selenocysteine is present at the active sites of certain human enzymes.

B. Selenocysteine is inserted into proteins by a posttranslational process.

C. Transamination of dietary α-keto acids can replace the dietary essential amino acids leucine, isoleucine, and valine.

D. Conversion of peptidyl proline to peptidyl-4-hydroxyproline is accompanied by the incorporation of oxygen into succinate.

E. Serine and glycine are interconverted in a single reaction in which tetrahydrofolate derivatives participate.

The insertion of selenocysteine into a peptide occurs during, not subsequent to translation.

Select the Correct answer:

The first reaction in the degradation of most of the protein amino acids involves the participation of:


B. Thiamine pyrophosphate (TPP)

C. Pyridoxal phosphate


E. NAD+ and TPP

Pyridoxal-dependent transamination is the first reaction in degradation of all the common amino acids except threonine, lysine, proline, and hydroxyproline.

Identify the amino acid that is the ...

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