Lecture_19_4-6-10-PDF_41576

Lecture_19_4-6-10-PDF_41576 - Lec 18, Amino Acid Metabolism...

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Lec 18, Amino Acid Metabolism 1. Protein degradation A. Lysosomal degradation B. Ubiquitin C. The proteosome 2. Amino acid deamination A. Transamination B. Oxidative deamination Lec 19 Amino Acid Metabolism 3. The Urea Cycle A. Reactions of the Urea Cycle B. Regulation of the Urea Cycle
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Synthesis and Degradation of Protein 1. Some amino acids are degraded and must be replaced through the diet 2. Growth requires that synthesis > degradation
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Amino Acids and Peptides in Small Intestine *Enterocyte Energy and Synthesis of Compounds Free Amino Acids Liver Amino Acid Utilization Potential breakdown of all amino acids as needed Synthesis of non-essential amino acids *intestinal absorptive cells
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Enterocyte
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Protein Free Amino acids Ammonia (urea) a -keto acid (recycle for other compounds) (waste) deamination ( a -keto acid) Protease/peptidase (waste)
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Deamination ( a -keto acid ) Citric acid (TCA) cycle Pepsin in the stomach Pancreatic proteases (trypsin, chymotrypsin, and, elastase) degrade polypeptide (protein) to oligopeptide and amino acids. However, further amino acid degradation requires the removal of the amine group (deamination).
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Degradation of amino acids (Lec 20)
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Deamination 1. Removal of amino group from an amino acid with no transfer 2. Produces ammonia and α-keto acid ammonia removed by urea cycle α-keto acid used for energy, etc. Transamination 1. Catalyzed by aminotransferases 2. Pyridoxal phosphate (PLP) required (B6)
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Transamination Deamination
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Figure 4-3 Condensation of two amino acids (peptide bond) Reminder
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Transamination Transaminases (aminotransferases) catalyze the reversible reaction . There are multiple transaminase enzymes which vary in substrate specificity. Some show preference for particular amino acids or classes of amino acids as amino group donors, and/or for particular a -keto acid (Carbon skeleton) acceptors.
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Glutamate can be recycled to a -KG for further deamination reactions or it can go into the TCA cycle (Lec-20, Ch 21-4)
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Transaminases equilibrate amino groups among available a -keto acids. Transaminases (aminotransferases) catalyze the reversible reaction . This permits synthesis of non-essential amino acids, using amino groups from other amino acids & carbon skeletons synthesized in a cell. Thus a balance of different amino acids is maintained , as proteins of varied amino acid contents are synthesized. Although the amino N of one amino acid can be used to synthesize another amino acid, N must be obtained in the diet as amino acids (proteins).
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Essential amino acids must be consumed in the diet. Mammalian cells lack enzymes to synthesize their carbon skeletons ( a -keto acids). These include:
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p764 “Th ese T en V aluable A mino acids H ave L ong P reserved L ife I n M an” They are easily (?) memorized using the mnemonic “V ery M any H appy L ittle P igs T ake I ced L emon T ea
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In another example, alanine becomes pyruvate as the amino group is transferred to a -KG.
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Lecture_19_4-6-10-PDF_41576 - Lec 18, Amino Acid Metabolism...

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