第二节脂肪酸的合代谢
第二节 脂肪酸的合成代谢
.甘油的合成 甘油的合成在细胞质中进行。 由糖酵解的中间产物磷酸二羟丙酮还原而成。 HC-OH NADHH NAD H2C-OH HO H2C-OH HO-CH HO-CH HC-0p0磷酸甘油脱氨酶C-0P03碜酸酯酶 HIC-OH 磷酸二羟丙酮 磷酸甘油 甘油 事实上,在甘油和脂肪酸缩合连结成脂肪时, 所需要的是3-磷酸甘油,而不是游离的甘油
一. 甘油的合成 由糖酵解的中间产物磷酸二羟丙酮还原而成。 甘油的合成在细胞质中进行。 事实上，在甘油和脂肪酸缩合连结成脂肪时， 所需要的是3-磷酸甘油，而不是游离的甘油
(一)脂肪酸的从头合成 脂肪酸的合成 部位: 动物体—细胞质 植物体—叶绿体和前质体 原料:乙酰CoA 产物:不超过16碳的饱和脂肪酸
(一) 脂肪酸的从头合成 二. 脂肪酸的合成 原料：乙酰CoA 产物：不超过16碳的饱和脂肪酸 部位： 动物体 —— 细胞质 植物体 —— 叶绿体和前质体
(一)脂肪酸的从头合成 脂肪酸的合成 Overview Fatty acids are synthesized by the condensation of two-carbon units. However in terms of the enzymic steps involved, the process is not the reversed of B-oxidation Fatty acid synthesis involves a separate series of reactions to build up long-chain hydrocarbons from acetyl CoA units. The key differences between fatty acid synthesis and breakdown are:
Overview Fatty acids are synthesized by the condensation of two-carbon units. However, in terms of the enzymic steps involved, the process is not the reversed of -oxidation. Fatty acid synthesis involves a separate series of reactions to build up long-chain hydrocarbons from acetyl CoA units. The key differences between fatty acid synthesis and breakdown are: (一) 脂肪酸的从头合成 二. 脂肪酸的合成
(一)脂肪酸的从头合成 脂肪酸的合成 1. fatty acid synthesis occurs in the cytosol of both prokaryotes and eukaryotes whereas their degradation occurs in the mitochondria of euKaryotes 2. fatty acid synthesis uses NADPh as the reductant whereas nadh is produced in B-oxidation 3. during their synthesis, fatty acids are covalent linked to an acyl carrier protein(ACP), as opposed to CoA in their degradation 4. the enzyme activities of fatty acid synthesis in higher organisms are present in a single polypeptide chain called fatty acid synthase, whereas in B-oxidation the individual activities are present on separate enzymes
1. fatty acid synthesis occurs in the cytosol of both prokaryotes and eukaryotes whereas their degradation occurs in the mitochondria of eukaryotes; 2. fatty acid synthesis uses NADPH as the reductant whereas NADH is produced in -oxidation; 3. during their synthesis, fatty acids are covalently linked to an acyl carrier protein (ACP), as opposed to CoA in their degradation; 4. the enzyme activities of fatty acid synthesis in higher organisms are present in a single polypeptide chain called fatty acid synthase, whereas in -oxidation the individual activities are present on separate enzymes. (一) 脂肪酸的从头合成 二. 脂肪酸的合成
(一)脂肪酸的从头合成 脂肪酸的合成 1.脂肪酸从头合成的过程 (1)乙酰CoA的来源和转运 Transport into the cytosol Fatty acids are synthesized in the cytosol, but acety Coa is produced from pyruvate in the mitochondria. Thus he acetyl coa must be transferred from the mitochondria into the cytosol to allow fatty acid synthesis to occur. However the inner mitochondrial membrane is not eadily permeable to this molecule. This problem is overcome by the condensation of acetyl coa with oxaloacetate to form citrate
1. 脂肪酸从头合成的过程 (一) 脂肪酸的从头合成 二. 脂肪酸的合成 (1) 乙酰CoA的来源和转运 Transport into the cytosol Fatty acids are synthesized in the cytosol, but acetyl CoA is produced from pyruvate in the mitochondria. Thus the acetyl CoA must be transferred from the mitochondria into the cytosol to allow fatty acid synthesis to occur. However, the inner mitochondrial membrane is not readily permeable to this molecule. This problem is overcome by the condensation of acetyl CoA with oxaloacetate to form citrate
(一)脂肪酸的从头合成 脂肪酸的合成 1.脂肪酸从头合成的过程 (1)乙酰COA的来源和转运 因为乙酰CoA在线粒体产生,乙酰CoA不能直 接穿过线粒体内膜,需要通过“拧檬酸穿梭”的 方式从线粒体基质到达细胞质,才能用于合成脂 肪酸
1. 脂肪酸从头合成的过程 (一) 脂肪酸的从头合成 二. 脂肪酸的合成 (1) 乙酰CoA的来源和转运 因为乙酰CoA在线粒体产生，乙酰CoA不能直 接穿过线粒体内膜，需要通过“柠檬酸穿梭”的 方式从线粒体基质到达细胞质，才能用于合成脂 肪酸
(一)脂肪酸的从头合成 脂肪酸的合成 (1)乙酰COA的来源和转运 线粒体内膜 线粒体基质 细胞质 柠檬酸 柠檬酸 CoA ATP 乙酰CoA-( 乙酰CoA(1)柠檬酸合酶 ADP+Pi (2)柠檬酸裂解 草酰乙酸 草酰乙酸 (3)苹果酸脱氢酶 NADH+H NADH+H (4)苹果酸酶 (3) NAD NAD (5)丙酮酸羧化醉 ADP+Pi 苹果酸 苹果酸 CO NADP NADPH+H( 丙酮酸“一 内酮酸
(一) 脂肪酸的从头合成 二. 脂肪酸的合成 (1) 乙酰CoA的来源和转运
mitochondrial Mitochondrial matrix membrane Cvto Fatty acy Fatty acyl- Fatty acyl-COA Fatty acid carnitine oxidation Amino Acetyl-CoA Amino acid catabolism acids Oxaloacetate Citrate Citrate Citrate Acetyl-COA ATP-citrate alst TCA cle Oxaloacetate NADH NADH Malate Malat Fatty dehydrogenase dehydrogenase NADT< acids NAD Malate< Malate ADP+② NADP NADH Malic Priva dehydrogenase carboxylase 2 NADPH NADT ATP +(CO, Pyruvate Pyruvate Glycols Glucose
(一) 脂肪酸的从头合成 二. 脂肪酸的合成
(一)脂肪酸的从头合成 脂肪酸的合成 1.脂肪酸从头合成的过程 (1)乙酰COA的来源和转运 循环的净结果是将乙酰CoA从线粒体转运到了细 胞质,同时也消耗了化学能ATP。 在植物体中,线粒体内产生的乙酰CoA先脱去 CoA以乙酸的形式运出线粒体,再在线粒体外由脂 酰CoA合成酶催化重新形成乙酰CoA
1. 脂肪酸从头合成的过程 (一) 脂肪酸的从头合成 二. 脂肪酸的合成 (1) 乙酰CoA的来源和转运 循环的净结果是将乙酰CoA从线粒体转运到了细 胞质，同时也消耗了化学能ATP。 在植物体中，线粒体内产生的乙酰CoA先脱去 CoA以乙酸的形式运出线粒体，再在线粒体外由脂 酰CoA合成酶催化重新形成乙酰CoA