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Lecture36outline - I Review In biological systems amino...

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I. Review • In biological systems amino acids are prepared from α -keto carboxylic acids and pyridoxamine phosphate • This reaction proceeds through imine formation, tautomerization, and imine hydrolysis to yield the amino acid and pyridoxal phosphate • Proteins are converted to amino acids by enzymes called proteases, and the amino acids can be used to prepare other proteins or can be metabolized • The metabolism of amino acids is basically the reverse of the synthesis sequence, with the amino acid reacting with pyridoxal phosphate to form an imine that tautomerizes to yield an α - keto carboxylic acid and pyridoxamine • The keto acid can react with thiamine to lose CO 2 and form acarboxylic acid derivative • When pyridoxamine is present in abundance and pyridoxal is needed, excess arginine is synthesized and converted to urea, which is excreted • Pyridoxal is also involved in amino acid decarboxylation, as seen in the conversion of L-Dopa to dopamine • Nucleic acids are comprised of nitrogen–containing heterocyclic bases bound to ribose or
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