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Chapt. 39

Chapt. 39. Ch. 39 Student Learning Outcomes : Explain basic synthesis of nonessential amino acids Uses glucose derivatives (glycolysis, TCA) N sources often other aa Describe important cofactors: PLP (from Vitamin B6) for transaminations FH 4 (tetrahydrofolate) for 1C;

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Chapt. 39

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  1. Chapt. 39 • Ch. 39 • Student Learning Outcomes: • Explain basic synthesis of nonessential amino acids • Uses glucose derivatives (glycolysis, TCA) • N sources often other aa • Describe important cofactors: • PLP (from Vitamin B6) for transaminations • FH4 (tetrahydrofolate) for 1C; • BH4 (tetrahydrobiopterin) for hydroxylation • (Phe → Tyr) • Explain general regulation of amino acid synthesis (feedback inhibition, transcription inhibition) • Degradation of aa often distinct from synthesis path

  2. Overview synthesis of nonessential amino acids • Overview synthesis of nonessential amino acids: • Met donates the S to Cys • C skeletons come from glucose, glycolysis, TCA compounds • Aa that can be synthesized are often used for other N cmpds: • Gly → purine, pyrimidine • Asp → purine, pyrimidine • Gln → neurotransmitter Fig. 39.1*

  3. Overview Degradation of amino acids • Overview: degradation of amino acids: • Gluconeogenic: Pyruvate, TCA intermediates • B. Ketogenic: Acetyl CoA, ketone bodies Fig. 2

  4. Some genetic disorders of amino acid metabolism • Degradation • path enzyme disease symptoms • Phe phe hydroxylase (PAH) PKU classic mental retardation • homogentisate oxidase alcaptonuria black urine, arthritis • Tyr fumarylacetoacetate hydrolase tyrosinemia I liver failure, death • tyrosine aminotransferase tyrosinemia II neurological • Met cystathionase cystathionuria benign • cystathionine b-synthase homocystinemia cardiovascular, • neurological • Gly glycine transaminase oxaluria type 1 renal failure • (Gly → oxalate) Ca-oxalate stones

  5. Metabolism of Phe/Tyr • Phe and Tyr: • PKU from absence PAH (autosomal recessive); 1/104 births; all babies tested; • give special diet of low Phe (essential aa) • High Phe in blood → neurological • Tyr is made from Phe • various defects in degradation • neurological, liver failure Fig. 39.15

  6. Cysteine metabolism • Cysteine metabolism: • C, N from Ser, S from Met • Met donates S to Cys via Homocys • Removal of –CH3 • Cystathionine precursor of Cys • Feedback regulation of synthase • Adjust for dietary Cys • Lack of synthase → homocyst(e)inemia Figs. 39.6 Cys

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