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Section VI: Metabolism of Proteins & Amino Acids

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

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

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

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

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

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

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

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

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A. α-Ketoglutarate

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B. 3-Phosphoglycerate

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C. Glutamate

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D. Aspartate

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E. Histamine

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

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

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

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

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

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

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

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

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Select the CORRECT answer:

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

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A. NAD+

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B. Thiamine pyrophosphate (TPP)

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C. Pyridoxal phosphate

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D. FAD

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E. NAD+ and TPP

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

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Identify the amino acid ...

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