Metabolism of lipids.

Presentation on theme: "Metabolism of lipids."— Presentation transcript:

1 Metabolism of lipids

2 Course Content Digestion and absorption of lipids
Triacylglycerol metabolism Phospholipid metabolism Cholesterol metabolism plasma lipoprotein metabolism

3 Summary Definition Classes Function fats : triacylglycerols, TG lipids
cholesterol, Ch lipids cholesteryl ester, CE lipoids phospholipids, PL glucolipids, GL Function

4 nomenclature Fatty acids：
Saturated fatty acids 14〜20C palmitic acid 16C stearic acid 18C Unsaturated fatty acids Linolenic acid 18C three unsaturated bonds Linoleate 18C two unsaturated bonds Arachidonic acid 20C four unsaturated bonds Essential fatty acids required for the growth of mammals and they must be obtained from food. Including linoleate、linolenate, arachidonic acid amount unsaturated in plant

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6 Section I Digestion and absorption of lipids
small intestine：bile、pancreatic lipase、colipase、phospholipase A2、 cholesteryl esterase product：2-monoacylglycerol(MG)、FFA、Cholesterol、lysophospholipid absorption

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8

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10 Absorption：

11 Monoacylglycerol synthesis Pathway

12 Section II Triacylglycerol metabolism

13 Chemical Structure of Triacylglycerol

14 Palmitic acid synthesis Elongation of FA carbon-chainER
Fatty Acid Synthesis Palmitic acid synthesis Elongation of FA carbon-chainER ER --Mitochondrial Synthesis of Unsaturated FA Regulation of unsaturated FA

15 Biosynthesis of palmitic Acid
Tissues：liver(major site) 、kidney、 breast、adipose、 lung 、 brain ---Cytosol Materials：Acetyl-CoA、NADPH+H+、ATP、HCO3- and Mn2+ Pathway ---Synthesis of malonyl-CoA ---Synthesis of fatty acid

16 Citrate Pyruvate Cycle

17 malonyl-CoA Synthesis
限速酶

18

19 The overall reaction, which is spontaneous, may be summarized as:
HCO3- + ATP + acetyl-CoA  ADP + Pi + malonyl-CoA

20 Acetyl-CoA Carboxylase, which converts acetyl-CoA to malonyl-CoA, is the committed step of the fatty acid synthesis pathway. The mammalian enzyme is regulated, by phosphorylation allosteric control by local metabolites. Conformational changes associated with regulation: In the active conformation, Acetyl-CoA Carboxylase associates to form multimeric filamentous complexes. Transition to the inactive conformation is associated with dissociation to yield the monomeric form of the enzyme (protomer).

21 AMP-Activated Kinase catalyzes phosphorylation of Acetyl-CoA Carboxylase, causing inhibition.
The decreased production of malonyl-CoA prevents energy-utilizing fatty acid synthesis when cellular energy stores are depleted. (AMP is abundant only when ATP has been extensively dephosphorylated.)

22 The antagonistic effect of insulin, produced when blood glucose is high, is attributed to activation of Protein Phosphatase.

23 Regulation of Acetyl-CoA Carboxylase by local metabolites:
Palmitoyl-CoA (product of Fatty Acid Synthase) promotes the inactive conformation, diminishing production of malonyl-CoA, the precursor of fatty acid synthesis. This is an example of feedback inhibition.

24 Citrate allosterically activates Acetyl-CoA Carboxylase.
[Citrate] is high when there is adequate acetyl-CoA entering Krebs Cycle. Excess acetyl-CoA is then converted via malonyl-CoA to fatty acids for storage.

25 Fatty acid synthesis from acetyl-CoA & malonyl-CoA occurs by a series of reactions that are:
in bacteria catalyzed by 6 different enzymes plus a separate acyl carrier protein (ACP) in mammals catalyzed by individual domains of a very large polypeptide that includes an ACP domain. NADPH serves as electron donor in the two reactions involving substrate reduction. The NADPH is produced mainly by the Pentose Phosphate Pathway.

26 Mammalian fatty acid synthase
A dimer of two polypeptides of 240 kDa each Each polypeptide contains eight domains that represent the seven catalytic centres plus an integral acyl carrier protein (ACP) domain

27 4′ phosphopantetheine

28 The structure of the mammalian Fatty Acid Synthase protein is summarized above KS = b-Ketoacyl Synthase (Condensing Enzyme)---(Cys) AT =Acyl transferase MT = Malonyl/Acetyl-CoA Transacylase DH = Dehydratase ER = Enoyl Reductase KR = b-Ketoacyl Reductase TE = Thioesterase ACP = Acyl Carrier Protein ---(Pant)

29 4. Reduction 5. Acyl transfer 3.Dehydration 1.Condensation 2.Reduction

30 Elongation of FA Carbon-chain
ER Mitochondria Synthesis of unsaturated FA unsaturated FA ：软油酸、Oleate、linoleate、linolenate、arachidonic acid （ Essential FA ） Essential FA：required for the growth of mammals and they must be obtained from food. Including linoleate、linolenate, arachidonic acid

31 如亚油酸：

32 Regulation of FA synthesis
Dietary factors: carbohydrate promotes synthesis Hormone factors insulin，“store hormone”，increase FA synthesis Glucagon ，“release hormon”，inhibit FA synthesis

33 Chemical structure and nomenclature of PG、 TX、 LT
Important of polyunsaturated fatty acids---prostaglandins (PG)、 thromboxanes (TX)、 leukotrienes (LT) Chemical structure and nomenclature of PG、 TX、 LT Synthesis of PG、TX and LT Physiological functions of PG、TX and LT

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35

36 Thromboxane A2 Leukotriene A4(LTA4)

37 Synthesis of PG、TX and LT

38 Physiological functions of PG、TX and LT
PG：PGE2 triggers inflammation；PGE2、PGA2 downregulates blood pressure；PGF2promotes ovulation、delivery TX：TXA2 and PGE2 promotes coagulation and thrombosis PGI2：inhibiting coagulation and thrombosis LT：Constriction of bronchial smooth muscle cells，Slow reaction substances（SRS-A）are mixtures of LTC4、LTD4and LTE4

39 本小节要求 掌握软脂酸合成的原料、限速酶；了解软脂酸合成过程及合成的调节。
熟悉前列腺素、血栓噁烷及白三烯合成的原料；了解其合成过程及生理功能。

40 Synthesis of Triglycerides location：liver、adipose tissue and small intestinal materials：glucose、dietary fats pathway：Acylglycerol pathway diacylglycerol pathway

41 Dietary (external) Fat synthesis(internal) CM FFA CM VLDL FFA mobilization

42 Diacylglycerol Pathway

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44 Degradation of Triacylglycerols
Lipolysis Glycerol Metabolism β-Oxidation Other oxydation modes of fatty acid Formation and utilization of Ketone Bodies

45 Lipolysis Concept Committed enzyme：hormone-sensitive triglyceride
lipase (HSL) Lipolysis hormones：adrenalin 、glucagon、ACTH and TSH Anti-lipolysis hormones：Insulin、PEGE2 and Nicotinic Acid

46 PPi ADP HSL (inactive) HSL (active) Pi P

47 lipolysis Glucagon Insulin ATP HSL adenylyl cyclase cAMP
Committed enzyme (+) (-) ATP HSL adenylyl cyclase (+) cAMP Protein kinase HSL- P (active) TG DG lipolysis FFA MG FFA glycerol

48 Glycerol metabolism

49 Experimental evidence for β-Oxidation of fatty acid

50 β-Oxidation of fatty acid
概念：脂肪酸氧化从羧基端β-碳原子开始，每次释放出一个二碳片段（acetyl-CoA） Steps：Activation of FAenter into mitochondria β-oxidation TAC(Tricarboxylic acid cycle)

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52 Activation of fatty acid — Formation of Acyl-CoA
Location：cytosol acyl-CoA

53 Carnitine (Acyl-CoA) (Carnitine)

54 Mitochondrion

55 Carnitine acyltransferase Ⅰ Carnitine acyltransferase Ⅱ
限速酶 CoASH Carnitine acyltransferase Ⅱ CoASH

56 Acyl CoA enter into mitochondrion
Committed enzyme

57 β-Oxidation of fatty acid
location：mitochondrial matrix 过程：在脂肪酸β-氧化多酶复合体的催化下，从脂酰基β碳原子开始，dehydrogenation 、加水hydration、dehydrogenation 、thiolysis四步，生成一分子比原来少两个碳原子的脂酰CoA(acyl-CoA)及一分子乙酰CoA(acetyl-CoA)

58 β α FAD (dehydrogenation) FADH H2O (hydration) NAD+ (dehydrogenation)
NADH CoASH (thiolysis)

59 (dehydrogenation) (hydration) (dehydrogenation) (thiolysis)

60 脂肪酸β-Oxidation要点 脂肪酸仅需活化一次（cytosol），消耗一个ATP的两个高能键；
Acyl-CoA由carnitine运入线粒体，限速酶：CAT-Ⅰ； β-Oxidation（mitochondrion）: including dehydrogenation 、hydration 、dehydrogenation 、thiolysis four repeated steps

61 脂肪酸氧化的能量生成 如软脂酸（C16）： formula：12 × +5 ×( -1) –2 能量利用率：
7次β-氧化，生成8分子乙酰CoA、7分子FADH2及7分子NADH 即 12 ×8 +2×7+3 ×7=131分子ATP 脂肪酸活化时消耗2个高能磷酸键 净生成131-2=129分子ATP formula：12 × +5 ×( -1) –2 能量利用率：

62 Difference between synthesis and degradation of palmitic Acid
location cytosol mitochondria Acyl carrier ACP CoA Two carbon- fragment Malonyl-CoA Acytel-CoA reducing equivalents NADPH FAD、NAD+ HCO3- and citrate needed Not needed Energy alteration Consume 7ATP＋14NADPH Form 129ATP

63 Difference Between Fatty Acid Synthesis And β-Oxidation
Diffference Synthesis β -Oxidation Location Cytoplasm Mitochondrion Thioester linkage ACP CoA Two carbon-fragment Malonyl-CoA Acetyl-CoA Electron carrier NADPH FADH、NADH HCO3- and cytratre needed Nod needed Energy alteration Consume 7ATP＋14NADPH Form 129ATP

64 Other oxydation modes of fatty acid
Oxydation of unsaturated FA FA oxydation in peroxisomes Oxydation of propionic acid

65 Formation and utilization of Ketone Bodies
Ketone Bodies：Acetoacetate、 β-Hydroxybutyrate and Acetone Ketogenesis Utilization of Ketone Bodies Physiology Significance of Ketogenesis Regulation of Ketogenesis

66 ketone bodies(KB) γ β α β-hydroxybutyrate Acetoacetate Acetone

67 CoASH CoASH 限速酶 CoASH β α NAD+ CO2 NADH H+

68 Formation of Ketone Bodies
限速酶

69 Utilization of Ketone Bodies

70 Liver Blood Extrahepatic Tissues
① ② Urine ⑥ ③ ⑦ ④ ⑤ Citric acid cycle Citric acid cycle Acetone Lungs

71 Major energy materials provided for tissues
Glucose FFA KB Red Blood Cell + Brain Muscle +(exercise) +(rest) Liver

72 Concentration of energy materials of the blood in full of eating or hungry (mmol/L)
Hungry(5-6 weeks) Glucose 5.0 4.49 β-Hydroxybutyrate 0.02 6.67 Acetoacetate 1.17

73 Physiology Significance of Ketogenesis
Ketone bodies serve as a fuel for extrohepatic tissues. Ketoacidosis results from prolonged ketosis:Higher than normal quantities of ketone bodies present in the blood or urine constitude ketonemia or ketonuria, respectively.The overall condition is called ketosis.

74 Three Crucial Steps for Ketogenesis Regulation
Control of free fatty acid(FFA) mobilization from adipose tissue The activity of carnitine acyltransferase (CAT-1) in liver,which determines the propotion of the fatty acid flux that is oxidized rather than esterified; Partition of acetyl-CoA between the pathway of ketogenesis and the citric acid cycle

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76 Regulation of Ketogenesis

77 复习题 名词解释 1、脂肪的动员(lipolysis)； 2、激素敏感性甘油三酯脂肪酶(HSL)； 3、脂解激素；
4、脂肪酸的β-氧化(β-oxidation)； 5、必需脂酸(essential fatty acid)； 6、酮体(ketone bodies)

78 问答 1、简述胆汁酸盐的生理作用。 2、简述酮体生成的生理意义。 3、写出甘油异生为葡萄糖的过程。
4、一分子三软脂酰甘油彻底氧化成CO2和H2O，产生多少分子ATP？写出代谢途径的全过程。

79 测试题 (A、B) 1、胆汁酸盐在 脂 类 消 化 中 主 要 作 用： A、 有 使 脂 肪 乳 化 的 作 用
C、 有 促 进 胰 脂 酶 活 性 的 作 用 D、 使 水 解 的 脂 类 呈 溶 解 状 态 E、 有 促 进 辅 脂 酶 活 性 的 作 用 (A、B)

80 测试题 (D) 2、参 与 脂 肪 酸 氧 化， 以 FAD 为 辅 基 的 酶 催 化 : A、 还 原 不 饱 和 脂 酰 CoA
B、 β-羟 脂 酰 CoA 脱 氢 C、 脂 肪 酸 的 激 活 D、 脂 酰 CoA 脱 氢 E、 β-酮 脂 酰 还 原 (D)

81 测试题 (A、C) 3、一分子14 碳的肉豆蔻酸经β-氧化为乙酰CoA A、活化肉豆蔻酸消耗2 分子高能磷酸键
B、肉豆蔻酸需经7次β-氧化才生成7分子乙酰CoA C、生成6 分子FADH2 和6 分子NADH + H+ D、肉毒碱脂酰转移酶Ⅱ是豆蔻酸β-氧化的关键酶 (A、C)

82 测试题 (A) 4、对脂酸分解代谢而言下列哪一种叙述是错误的？ A、存在于胞液 B、生成CH3CO~CoA
C、β氧化的活性形式是RCH2CH2CH2CO~CoA D、一种中间物是RCH2CHOHCH2CO~CoA E、反应进行时NAD+→NADH (A)

83 测试题 5、彻底氧化1分子硬脂酰CoA（18：0）共需消耗多少分子O2？ A、 B、 C、30 D、 E、32 (B)

84 测试题 (A、B、C、D) 6、有关酮体的正确叙述是： A、酮体包括丙酮、乙酰乙酸和β-羟丁酸 B、酮体可以从尿中排出

85 测试题 7、能将酮体氧化成CO2和H2O的组织是 A、心肌 B、红细胞 C、脑 D、肝 (A、C)

86 本小节要求 掌握软脂酸合成的原料、限速酶；了解软脂酸合成过程及合成的调节。 熟悉前列腺素、血栓噁烷及白三烯合成的原料。

87 Section II Phospholipid Metabolism

88 Classification of Phospholipids
phosphoglyceride Phosphatidylcholine (PC) Phosphatidylethanolamine (PE) Phosphatidylserine (PS) Phosphatidylglycerol (PG) Diphosphatidylglycerol (DPG) phosphatidyl inositol(PI) Sphingomyelin

89 Chemical Structure of Phosphoglyceride
Most phospholipids have a saturated fatty acid on C-1 and an unsaturated fatty acid (Arachidonic Acid )on C-2 of the glycerol backbone.

90 Structure of Phospholipid

91 Classification of phosphoglyceride-1
X-OH X name

92 Classification of phosphoglyceride-2
X-OH X name

93 Glycerophospholipid synthesis
Site: liver，kidney，intestine endoplasmic reticulum, ER Sources：FA，glycerol，phosphate，nitrogenous base （choline，ethanolamine，serine，inostol,etc），ATP, CTP CDP- nitrogenous base CDP-diacylglycerol

94 CDP-choline与CDP- diacylglycerol

95 Diacylglycerol Pathway

96 Diacylglycerol Pathway—PE, PC

97 CDP- Diacylglycerol Pathway—PI、PS、DPG

98 Synthesis of CDP- nitrogenous base

99 Phosphoglycerol degradation

100 Metabolism of Sphingolipids
Sphingomyelins and Glycosphingolipids X=Phosphorylcholin or phosphoethanolamine X=Mono-or Poly- saccharin Sphingomyelin Glycosphingolipid

101 Synthesis and Degradation of Sphingomyelin
Site: brain---ER Souces:palmitoyl-CoA, Serine,NADPH+H,FAD Pathway:

102 Degradation of Sphingomyelin
Sphingomyelinase (PLC ) -----Defects in the enzymes result in genetic diseases such as Niemann- Pick disease

103 本小节要求 熟悉常见甘油磷脂的名称、组成、合成原料及CTP的作用；了解各种磷脂酶作用的部位。

104 作业题 1、以下两题任选一题（必做） 2、请用代谢图将糖类与脂类的合成与分解代谢联系起来。（必做） 3、简述甘油磷脂合成的原料及辅助因子。
吃的多动的少容易长胖，试从生化角度分析其原因。 从生化角度谈谈你对减肥的认识。 2、请用代谢图将糖类与脂类的合成与分解代谢联系起来。（必做） 3、简述甘油磷脂合成的原料及辅助因子。 4、葡萄糖如何为脂酸合成提供原料？

105 测试题 彻底氧化1分子硬脂酰CoA（18：0）共需消耗多少分子O2？ A、 B、 C、30 D、 E、32 (B)

106 复习题 (B) 1、关于脂酸生物合成的途径正确的是： A、不需乙酰CoA B、中间产物是丙二酰CoA C、在线粒体内进行
D、以NADH为还原剂 E、最终产物为十碳以下脂酸 (B)

107 复习题 (B) 2、脂酸合成所需的乙酰CoA由 A、胞浆直接提供 B、线粒体合成并转化为柠檬酸转运到胞浆 C、胞浆的乙酰肉毒碱提供
D、线粒体合成，以乙酰CoA的形式 E、胞浆的乙酰磷酸提供 (B)

108 复习题 3、下列磷脂中哪一个含有胆碱？ A、脑磷脂 B、卵磷脂 C、磷脂酸 D、心磷脂 (B)

109 复习题 4、合成卵磷脂时所需的活性胆碱是 A、TDP-胆碱 B、ADP-胆碱 C、UDP-胆碱 D、GDP-胆碱 E、CDP-胆碱 (E)

110 Section IV Cholesterol(Ch) Metabolism

111 Cholesterol Structure
Cholesterol(Ch) Cholesterol Ester(CE) 环戊烷多氢菲

112

113 Roles of Cholesterol Membrane component Steroid synthesis
Bile acid/salt precursor Vitamin D precursor

114 Sources of Cholesterol
Cholesterol synthesized in extrahepatic tissues De novo synthesis Diet Liver cholesterol pool Secretion of HDL and VLDL Free cholesterol In bile Conversion to bile salts/acids

115 Dietary Cholesterol Animal products – eggs Absorb about 50%
Increase intake = decreased absorption Excrete – 1 g/day (bile acids)

116 Dietary Cholesterol Assume 400 mg intake / day 200 mg is absorbed
1000 mg is excreted 800 mg from de novo synthesis Lowering cholesterol in diet has very little effect on blood cholesterol !!!

117 Cholesterol Synthesis
80 % in liver, ~10% intestine, ~5% skin Occurs in cytosol Requires 18Acetyl-CoA、16NADPH、36ATP Similar to ketogenic pathway Highly regulated

118 Cholesterol Synthesis-1
限速酶

119 Cholesterol Synthesis -2

120 Cholesterol Synthesis
Summary

121 Regulation of Cholesterol Synthesis
rate-limiting enzyme：HMGCoA reductase Regulation factors： Famine and saturation: famine (-), fasting (-) cholesterol inactivate HMGCoA reductase Hormons: insulin/thyroxin induce activity of HMGCoA reductase; glucagon/cortisol/Epi inactivate HMGCoA reductase

122 HMG CoA reductase - Phosphorylation
HMG CoA reductase – OH (active) HMG CoA reductase – P (inactive) AMP-Activated Protein Kinase (high activity) (+) AMP phosphatase kinase (+) (+) AMP-Activated Protein Kinase (low activity) increase cAMP Insulin Glucagon/epi

123 Conversion of Cholesterol
Bile acid: liver (2/5) Steroids: adrenal cortex, testicle,ovary Vitamin D: skin(7-dehydrocholeterol and Vitamin D3)

124 本小节要求 掌握胆固醇结构特点、合成原料、限速酶；了解其合成过程；熟悉胆固醇的转化产物。
熟悉各种血脂的分类、组成特点；掌握其功能；了解载脂蛋白的功能；

125 Section IV Metabolism of Plasma Lipoproteins
Plasma lipids Plasma lipoproteins Apolipoproteins Metabolism of Plasma Lipoproteins Medical implications

126 Plasma Lipids ----Lipids in plasma
TG：100mg/dl PL： 200mg /dl lecithins % nerve sphingomyelin % cephalin % Ch and CE：200mg /dl Ch:55mg /dl; CE:145mg /dl FFA：15mg /dl Origin of plasma lipids： Exogenous: dietary lipids Endogenous: synthetized by liver, adipose tissue and other tissues

127 Plasma Lipoproteins Classes：
electrophoresis：CM (Chylomicron) 、β、 pro-β、α ultracentrifugation： CM、VLDL(very low density lipoprotein)、LDL、HDL

128

129 Compositions of plasma lipoproteins

130 Structure of plasma lipoprotein

131

132 Apolipoproteins (apo) -1
Type Association Function B48 Chylomicron Carry cholesterol esters Lacks LDL recpt binding domain B100 VLDL,IDL,LDL Binds LDL recpt. C-II Chyl. VLDL, IDL, HDL Activates LPL C-III Chyl. VLDL, IDL, HDL Inhibits LPL E Chyl. Remnant, VLDL, IDL Binds LDL recpt HDL A-1 HDL/Chylomicron LCAT activator (lecithin:cholesterol acyltransferase) AⅡ HDL HL(+)；稳定HDL AⅣ HDL,CM LPL(+)

133 Apolipoprotein (apo) -2
Type Association Function D HDL transports CE J HDL binds and transports lipids CETP HDL transports CE,TG PTP HDL transports PL

134 Major Enzymes for Lipoprotein Metabolism
lipoprotein lipase,LPL hepatic lipase,HL lecithin: cholesterol acyltransferase, LCAT acyl-CoA: cholesterol acyltransferase, ACAT

135 lipoprotein lipase，LPL
hepatic lipase，HP

136 lecithin: cholesterol acyltransferase, LCAT

137 acyl-CoA: cholesterol acyltransferase,ACAT

138

139

140

141 CM Metabolism apoCⅡ激活LPL

142

143 VLDL Metabolism apoCⅡ激活LPL

144 CE

145 LDL Metabolism

146

147 HDL Metabolism

148 Function of plasma lipoproteins
CM：Transport dietary from intestine to liver (exogenous) VLDL: Transport lipids from liver to peripheral tissues (endogenous LDL：endogenous Cholesterol transport HDL：reverse Cholesterol transport

149 Clinical importance for disease
Hypertriglyceridemia and CHD Risk: Associated Abnormalities Accumulation of chylomicron remnants Accumulation of VLDL remnants Generation of small, dense LDL Association with low HDL Increased coagulability -  plasminogen activator inhibitor (PAI-1) -  factor VIIc - Activation of prothrombin to thrombin

150 LPL Deficiency LDL receptor Deficiency
Genetic Disease LPL Deficiency LDL receptor Deficiency

151 本小节要求 熟悉各种血脂的分类、组成特点；掌握其功能；熟悉载脂蛋白的功能；
熟悉各种血脂来源及最终代谢去路、LDL代谢途径；了解不同脂蛋白代谢之间的关系。

152 复习题 一、名词解释 1、血脂；2、血浆脂蛋白；3、载脂蛋白 二、问答 1、简述胆固醇的转化产物。
2、试述血浆脂蛋白的分类（电泳法、超速离心法）、合成部位及功能。

153 选择题练习 脂代谢

154 1. 脂肪动员的限速酶是( ) A 激素敏感性脂肪酶(HSL) B 胰脂酶 C 脂蛋白脂肪酶 D 组织脂肪酶 E 辅脂酶

155 2. 下列不能促进脂肪动员的激素是( ) A 胰高血糖素 B 肾上腺素 C ACTH D 促甲状腺素 E 胰岛素

156 3. 下列物质在体内彻底氧化后,每克释放能量最多的是( )
A 葡萄糖 B 糖原 C 脂肪 D 胆固醇 E 蛋白质

157 4. 脂肪酸氧化分解的限速酶是( ) A 脂酰CoA合成酶 B 肉碱脂酰转移酶I C 肉碱脂酰转移酶II D 脂酰CoA脱氢酶 E -羟脱氢酶

158 5. 脂肪酰进行-氧化的酶促反应顺序为( ) A 脱氢,脱水,再脱氢,硫解 B 脱氢,加水,再脱氢,硫解 C 脱氢,再脱氢,加水, 硫解 D 硫解,脱氢,加水,再脱氢 E 缩合,还原,脱水,再还原

159 6. 严重饥饿时,脑组织的能量主要来源于( ) A 糖的氧化 B 脂肪酸的氧化 C 氨基酸的氧化 D 乳酸氧化 E 酮体氧化

160 7. 通常生物膜中不存在的脂类是( ) A 脑磷脂 B 卵磷脂 C 胆固醇 D 甘油三酯 E 糖脂

161 8. 下列关于HMG-CoA还原酶的叙述哪项事错误的( )
B 是胆固醇合成过程中的限速酶 C 胰岛素可以诱导此酶合成 D 经磷酸化后活性可增强 E 胆固醇可反馈抑制其活性

162 9. 家族性高胆固醇血症纯合子的原发行代谢障碍是( )
A 缺乏载脂蛋白B B 由VLDL生成LDL增加 C 细胞膜LDL受体功能缺陷 D 肝脏HMG-CoA还原酶活性增加 E 脂酰胆固醇脂酰转移酶(ACAT)活性降低

163 10. 下列有关脂酸合成的叙述不正确的是( ) A 脂肪酸合成酶系存在于胞液中 B 脂肪酸分子中全部碳原子来源于丙二酰CoA C 生物素是辅助因子 D 消耗ATP E 需要NADPH参与

164 11. The organ having the strongest ability of fatty acid synthesis is ( )
A fatty tissue B lacteal gland C liver D kidney E brain

165 12. Which one transports cholesterol from outer to inner of liver?
A CM B VLDL C LDL D HDL E IDL

166 13. Which one is essential fatty acid?
A palmitic acid B stearic acid C oleinic acid D octadecadienoic acid E eicosanoic acid

167 14. The main metabolic outlet of body cholesterol is ( )
A change into cholesterol ester B change into vitamine D3 C change into bile acid D change into steroid hormone E change into dihydrocholesterol

168 15. 下列物质中与脂肪消化吸收有关的是( ) A 胰脂酶 B 脂蛋白脂肪酶 C 激素敏感性脂肪酶 D 辅脂酶 E 胆酸

169 16. 合成甘油磷脂共同需要的原料有( ) A 甘油 B 脂肪酸 C 胆碱 D 乙醇胺 E 磷酸盐

170 17. 参与血浆脂蛋白代谢的关键酶( ) A 激素敏感性脂肪酶(HSL) B 脂蛋白脂肪酶(LPL) C 肝脂肪酶(HL) D 卵磷脂胆固醇酰基转移酶(LCAT) E 脂酰基胆固醇脂酰转移酶(ACAT)

171 18. 脂蛋白的结构是( ) A 脂蛋白呈球状颗粒 B 脂蛋白具有亲水表面和疏水核心 C 载脂蛋白位于表面 D CM VLDL主要以甘油三酯为核心 E LDL HDL主要以胆固醇酯为核心

172 19. Which can be the source of acetyl CoA?
A glucose B fatty acid C ketone body D cholesterol E citric acid

173 20. The matters which join in synthesis of cholesterol directly are ( )
A acetyl CoA B malonyl CoA C ATP D NADH E NADPH