tailieunhanh - Ebook High-Yield biochemistry (3rd edition): Part 2

(BQ) Part 2 book "High-Yield biochemistry" presents the following contents: Amino acid metabolism, nucleotide metabolism, nutrition, gene expression, biochemical technology, hormones. Invite you to consult. | Chapter7. . . Amino Acid Metabolism Functions of Amino Acids A. The synthesis of new proteins requires amino acids. The primary source of amino acids is dietary protein. Breakdown of tissue proteins also provides amino acids. B. Amino acids provide nitrogen-containing substrates for the biosynthesis of 1. Nonessential amino acids 2. Purines and pyrimidines 3. Porphyrins 4. Neurotransmitters and hormones C. The carbon skeletons of the surplus amino acids not needed for synthetic pathways serve as fuel. They may be 1. Oxidized in the tricarboxylic acid TCA cycle to produce energy. 2. Used as substrates for gluconeogenesis. 3. Used as substrates for fatty acid synthesis. Removal of Amino Acid Nitrogen A. DEAMINATION the first step in metabolizing surplus amino acids yields an a-keto acid and an ammonium ion NH4 . B. TRANSDEAMINATION accomplishes deamination through the sequential actions of the enzymes aminotransferase transaminase and glutamate dehydrogenase Figure 7-1 . C. The appearance of aspartate aminotransferase AST or alanine aminotransferase ALT in the blood is an indication of tissue damage especially cardiac muscle AST and the liver AST and ALT . Urea Cycle and Detoxification of NH A. NH is toxic to the human body particularly the central nervous system CNS . B. NH4 IS CONVERTED TO UREA in the liver via the urea cycle. Urea is excreted in the urine Figure 7-2 . 45 46 CHAPTER 7 COOH I COOH I C-H I R Aminotransferase CO I R a-Ketoglutarate L-Glutamate Glutamate dehydrogenase NAD NADH H a-Ketoglutarate Figure 7-1 Deamination of an amino acid by the sequential action of an aminotransferase and glutamate dehydrogenase. a-Ketoglutarate and glutamate are a corresponding a-keto acid-amino acid pair. PLP pyridoxal phosphate activation e inhibition italicized terms enzyme names. C. IN PERIPHERAL TISSUES detoxification of NH4 which is ultimately converted to urea in the liver occurs by different mechanisms. 1. In most tissues the enzyme glutamine synthetase .