第七章糖代谢研究报告.pptVIP

第三节 糖酵解（glycolysis） （P63） In 1897, Eduard Buchner (Germany), accidental observation : sucrose (as a preservative) was rapidly fermented into alcohol by cell-free yeast extract. The accepted view that fermentation is inextricably tied to living cells (i.e., the vitalistic dogma) was shaken and Biochemistry was born: Metabolism became chemistry! In 1900s, Arthur Harden and William Young (Great Britain) found that Pi is needed for yeast juice to ferment glucose, a hexose diphosphate (fructose 1,6-bisphosphate) was isolated. They also separated the yeast juice into two fractions: one heat-labile, nondialyzable zymase (enzymes) and the other heat-stable, dialyzable cozymase (metal ions, ATP, ADP, NAD+). 1910s-1930s, Gustav Embden and Otto Meyerhof (Germany), studied muscle and its extracts: Reconstructed all the transformation steps from glycogen to lactic acid in vitro; revealed that many reactions of lactic acid (muscle) and alcohol (yeast) fermentations were the same! Discovered that lactic acid is reconverted to carbohydrate in the presence of O2 (gluconeogenesis); observed that some phosphorylated compounds are energy-rich. The whole pathway of glycolysis (from glucose to pyruvate) was elucidated by the 1940s. 一、糖酵解的概念 在无氧条件下，葡萄糖进行分解，形成2分子丙酮酸并提供能量的过程。 是一切生物有机体中普遍存在的葡萄糖降解的途径。 又称Embden -Meyerhof –Parnas途径，简称EMP途径 碳水化合物进入酵解途径的前奏 除葡萄糖以外，其他碳水化合物通过酵解进入分解代谢，必须首先转变为酵解途径的任一中间物。 最重要的是贮存多糖（淀粉和糖元）、二糖（麦芽糖、乳糖、蔗糖、海藻糖）及单糖（果糖、甘露糖、半乳糖）。 糖原和淀粉通过相应的磷酸化酶、磷酸葡萄糖变位酶生成G-6-P进入酵解。其他单糖可形成多个分支点的中间物进入酵解。 二、 EMP途径的生化历程 场所：细胞质 第一阶段：已糖的磷酸化 第二阶段：磷酸已糖的裂解 第三阶段：ATP及丙酮酸的生成 在每一阶段中，又包含若干反应 糖酵解概述 糖酵解概述 1摩尔葡萄糖酵解所产生的ATP摩尔数 A net gain of two ATP, two NADH, two molecules of pyruvate are resulted when a glucose molecule is oxidized via the glycolysis pathway: Glucose + 2 ADP + 2Pi + 2NAD+? 2 pyruvate + 2ATP + 2H2O + 2NADH + 2H+ ?Go = -146 kJ/mol 三、丙酮酸的去路 1）无氧条件下，丙酮酸转变为乳酸。 2）无氧条件下，丙酮酸转变为乙醛，进而生成乙醇。 3）有氧条件下，丙酮酸氧化脱羧生成乙酰-CoA，进入三羧酸循环，氧化供能（乙酰-CoA在能量状态高的情况下可用于合成脂类物质）。