tailieunhanh - Ebook Essentials of biochemistry: Part 2

(BQ) Part 2 book "Endocrine physiology" presents the following contents: Carbohydrate metabolism A - Glycolysis and gluconeogenesis; the tricarboxylic acid cycle; carbohydrate metabolism B: Di-, Oligo-, and polysaccharide synthesis and degradation; lipid metabolism, amino acid metabolism; nucleotide metabolism, photosynthesis; DNA, RNA, and protein metabolism. | Chapter 8 Carbohydrate Metabolism A Glycolysis and Gluconeogenesis Glycolysis is defined as the anerobic conversion of glucose to pyruvic acid. The glycolytic pathway which is ubiquitous in nature is also known as the Meyerhoff Embden Parnas pathway named after the three biochemists who made major contributions to its formulation. The physiological role played by glycolysis in the cell far exceeds just the biosynthesis of pyruvate . it provides the cell with ATP under anerobic conditions and it also supplies precursors for the biosynthesis of proteins lipids nucleic acids and polysaccharides. The enzymes involved in glycolysis ten in number are water soluble and are found in the cell cytoplasm. Historically these enzymes have received more scrutiny by biochemists than any other class of biochemical catalysts. As in all biochemical pathways a number of glycolytic enzymes are regulated by small molecules. The primary regulatory enzymes in this pathway are phosphofructoki-nase1 PFK1 and pyruvate kinase. In some tissues hexokinase is also a regulated enzyme . it has been called the pacemaker of glycolysis in brain and the red blood cell. In most mammalian tissues however hexokinase is not a regulated enzyme. Glycolysis Figure illustrates the glycolytic metabolic pathway. In Fig. there are three thermodynamically irreversible steps . reactions where the DG0 is highly negative. These reactions involve the enzymes hexokinase phosphofructokinase1 PFK1 and pyruvate kinase all indicated in red . The overall reaction for glycolysis is glucose 2NAD 2ADP3 2Pi2- 2pyruvate1 2NADH 2ATP4 2H . In terms of energetics four ATP molecules are synthesized two at the phosphoglycerate kinase step and two more when phosphoenolpyruvate is converted to . Fromm and . Hargrove Essentials of Biochemistry 163 DOI 978-3-642-19624-9_8 Springer-Verlag Berlin Heidelberg 2012 164 8 Carbohydrate Metabolism A Glycolysis and Gluconeogenesis H0H HO H CH2 H H H OH .