脂肪酸的代謝

1、二、 其他脂類的生物合成biosynthesis of phosphatidic acid. a fatty acyl group is activated by formation of the fatty acylcoa, then transferred to ester linkage with l-glycerol 3-phosphate, formed in either of the two ways shown. phosphatidic acid is shown here with the correct stereochemistry at c-2 of the glyc

2、erol molecule. to conserve space in subsequent figures, both fatty acyl groups of glycerophospholipids, and all three acyl groups of triacylglycerols, are shown projecting to the right.phosphatidic acid in lipid biosynthesis. phosphatidic acid is the precursor of both triacylglycerols and glyceropho

3、spholipids. the mechanisms for head-group attachment in phospholipid synthesis are described later in this section.1.三酰甘油的合成some of the fatty acids released into the blood are used for energy (in muscle, for example), and some are taken up by the liver and used in triacylglycerolsynthesis. the triac

4、ylglycerol formed in the liver is transported in the blood back to adipose tissue, where the fatty acid is released by extracellular lipoprotein lipase, taken up by adipocytes, and reesterifiedthe triacylglycerol cycle. in mammals, triacylglycerol molecules are broken down and resynthesized in a tri

5、acylglycerol cycle during starvation. some of the fatty acids released by lipolysis of triacylglycerol in adipose tissue pass into the bloodstream, and the remainder are used for resynthesis of triacylglycerol. insulin stimulates conversion of dietary carbohydrates and proteins to fat. individuals w

6、ith diabetes mellitus lack insulin; in uncontrolled disease, this results in diminished fatty acid synthesis, and the acetyl-coa arising from catabolism of carbohydrates and proteins is shunted instead to ketone body production. people in severe ketosis smell of acetone, so the condition is sometime

7、s mistaken for drunkenness.regulation of triacylglycerol synthesis by insulinglyceroneogenesis. the pathway is essentially an abbreviated version of gluconeogenesis, from pyruvate to dihydroxyacetonephosphate (dhap), followed by conversion of dhap to glycerol 3-phosphate, which is used for the synth

8、esis of triacylglycerol.regulation of glyceroneogenesis. (a) glucocorticoid hormones stimulate glyceroneogenesis and gluconeogenesis in the liver, while suppressing glyceroneogenesis in the adipose tissue (by reciprocal regulation of the gene expressing pep carboxykinase (pepck) in the two tissues);

9、 this increases the flux through the triacylglycerol cycle. the glycerol freed by the breakdown of triacylglycerol in adipose tissue is released to the blood and transported to the liver, where it is primarily converted to glucose, although some is converted to glycerol 3-phosphate by glycerol kinas

10、e. thiazolidinediones activate a nuclear receptor called peroxisome proliferator-activated receptor (ppar), which induces the activity of pep carboxykinase. therapeutically, thiazolidinediones increase the rate of glyceroneogenesis, thus increasing the resynthesis of triacylglycerol in adipose tissu

11、e and reducing the amount of free fatty acid in the blood.(b) a class of drugs called thiazolidinediones are now used to treat type 2 diabetes. in this disease, high levels of free fatty acids in the blood interfere with glucose utilization in muscle and promote insulin resistance.2.真核細(xì)胞中磷脂的合成two ge

12、neral strategies for forming the phosphodiester bond of phospholipids. in both cases, cdp supplies the phosphate group of the phosphodiester bond.initially, a head group (either serine or glycerol 3-phosphate) is attached via a cdpdiacylglycerolintermediate. for phospholipids other than phosphatidyl

13、serine, the head group is further modified, as shown here. in the enzyme names, pg represents phosphatidylglycerol; ps, phosphatidylserine.origin of the polar head groups of phospholipids in e. colithese glycero-phospholipids are synthesized using strategy 1. phospha-tidylglycerol is synthesized as

14、in bacteria. pi represents phospha-tidylinositol.synthesis of cardiolipin and phosphatidylinositol in eukaryotesthe “salvage” pathway from phosphatidylserine tophosphatidylethanolamine and phosphatidylcholine in yeast. phosphatidylserine and phosphatidylethanolamine are interconverted by a reversibl

15、e head-group exchange reaction. in mammals, phosphatidylserine is derived from phosphatidylethanolamine by a reversal of this reaction; adomet is s-adenosylmethionine; adohcy, sadenosylhomocysteine.pathway for phosphatidylcholine synthesis from choline in mammals. the same strategy shown here (strat

16、egy 2) is also used for salvaging ethanolamine in phosphatidylethanolamine synthesis.summary of the pathways to phosphatidyl-choline andphosphatidyl-ethanolamine. conversion of phosphatidyl-ethanolamineto phosphatidyl-choline in mammals takes place only in the liver.真核細(xì)胞中磷脂的合成（綜合1 ）真核細(xì)胞中磷脂的合成（綜合2）哺乳

17、動(dòng)物磷脂酰膽堿和磷脂酰乙醇氨的相互轉(zhuǎn)化真核細(xì)胞中cdp-二酰甘油是合成磷脂酰肌醇，磷脂酰甘油，心磷脂的前體。3.動(dòng)物細(xì)胞中縮醛磷脂的合成血小板活化因子:1-烷基-2-乙酰甘油磷酸膽堿的合成4.鞘脂的生物合成由3-酮鞘氨醇合成酶催化的反應(yīng)開(kāi)始3-酮鞘氨醇二氫鞘氨醇n-脂酰二氫鞘氨醇神經(jīng)酰胺動(dòng)物細(xì)胞中糖基神經(jīng)酰胺，神經(jīng)節(jié)苷脂和鞘磷脂的由神經(jīng)酰胺合成。鞘磷脂5.花生四烯酸是合成前列腺素，血拴烷和白三烯的前體。前列腺素內(nèi)過(guò)氧化物合成酶催化pgh2的合成阿斯匹林使環(huán)加氧酶失活5.膽固醇的合成甲羥戊酸的合成甲羥戊酸合成的機(jī)制hmg-coa還原酶的活力受合成速度、降解速度及磷酸化和脫磷酸調(diào)控。甲羥戊酸到鯊烯

18、的轉(zhuǎn)化oxidation at c-15 converts retinol to the aldehyde, retinal (c), and further oxidation produces retinoic acid (d), a hormone that regulates gene expression. retinal combines with the protein opsin to form rhodopsin (not shown), a visual pigment widespread in nature. in the dark, retinal of rhodop

19、sin is in the 11-cis form (c). when a rhodopsin molecule is excited by visible light, the 11-cis-retinal undergoes a series of photochemical reactions that convert it to all-trans-retinal (e), forcing a change in the shape of the entire rhodopsin molecule. this transformation in the rod cell of the

20、vertebrate retina sends an electrical signal to the brain that is the basis of visual transduction.(a) -carotene is the precursor of vitamin a1. isoprene structural units are set off by dashed red lines. cleavage of -carotene yields two molecules of vitamin a1 (retinol) (b). vitamin a1 and its precu

21、rsor and derivatives由鯊烯轉(zhuǎn)化為膽固醇豆甾醇豆甾醇麥角甾醇麥角甾醇 膽固醇的合成是一個(gè)高度耗能的過(guò)程，合成一個(gè)膽固醇需18個(gè)乙酰輔酶a，36個(gè)atp，16個(gè)nadph。能源物質(zhì)過(guò)剩時(shí)，膽固醇的合成速度加快，午夜時(shí)，合成速度較快，膳食固醇類，特別是植物固醇可抑制膽固醇的合成。lipoproteins. (a) structure of a low-density lipoprotein (ldl). apolipoprotein b-100 (apob-100) is one of the largest single polypeptide chains known, wi

22、th 4,636 amino acid residues (mr 513,000). (b) four classes of lipoproteins, visualized in the electron microscope after negative staining. clockwise from top left: chylomicrons, 50 to 200 nm in diameter; vldl, 28 to 70 nm; hdl, 8 to 11 nm; and ldl, 20 to 25 nm. 脂類是由脂蛋白運(yùn)輸?shù)膌ipoproteins and lipid tran

23、sport. (a) lipids are transported in the bloodstream as lipoproteins, which exist as several variants that have different functions, different protein and lipid compositions, and thus different densities. dietary lipids are packaged into chylomicrons; much of their triacylglycerol content is release

24、d by lipoprotein lipase to adipose and muscle tissues during transport through capillaries. chylomicron remnants (containing largely protein and cholesterol) are taken up by the liver. endogenous lipids and cholesterol from the liver are delivered to adipose and muscle tissue by vldl.extraction of l

25、ipid from vldl (along with loss of some apolipoproteins) gradually converts some of it to ldl, which delivers cholesterol to extrahepatic tissues or returns to the liver. the liver takes up ldl, vldl remnants, and chylomicron remnants by receptor-mediated endocytosis. excess cholesterol in extrahepa

26、tic tissues is transported back to the liver as hdl. in the liver, some cholesterol is converted to bile salts.(b) blood plasma samples collected after a fast (left) and after a high-fat meal (right). chylomicrons produced after a fatty meal give the plasma a milky appearance.reaction catalyzed by l

27、ecithin-cholesterol acyl transferase (lcat). this enzyme is present on the surface of hdl and isstimulated by the hdl component apoa-i. cholesteryl esters accumulatewithin nascent hdls, converting them to mature hdls.載脂蛋白在肝細(xì)胞內(nèi)質(zhì)網(wǎng)合成，在內(nèi)質(zhì)網(wǎng)組裝成脂蛋白顆粒，在高爾基體加工，包裝成分泌小泡，分泌到肝細(xì)胞外。脂蛋白顆粒的胞吞和降解ldl受體的結(jié)構(gòu)srebp activation. sterol regulatory element-binding proteins (srebps, shown in green) are embedded in the