Chapter 5 lipids metabolism
Jan 13, 2016
Chapter 5
lipids metabolism
LIPIDS
• Water-insoluble substances that can be extracted from cells by nonpolar organic solvents
• Characteristics of fat• Hydrophobic because of nonpolar FA chain
• Lipids store large amounts of energy• 9 kcal/gram due to energy rich fatty acid chain
Outline
• Classification of FA and Nomenclature
• Digestion of Triacylglycerols
• Metabolism of TAG
• Metabolism of phospholipids
• Metabolism of cholesterol
• Lipoproteins metabolism
Section 1 Classification of FA and Nomenclature (命名)
• According to the number of carbon atom:
short chain(2~4C), medium chain (6~10C) & long chain(12~26C) fatty acid
• According to whether it contains double bond or not
(saturate & unsaturate fatty acid)
• According to the number of carbon atom, the source & property. such as: Butyric acid, Arachidonic acid
• systemic nomination
( catalogue, or n catalogue)
Classification and Functions of Lipids
1. Triglyceride, TG ( Variable lipids ) :
- As storage and transport form of metabolic fuel - To keep the body temperature - Fats are solids; oils are liquids - To protect the visceras2. Lipoid ( Basic lipids ): Cholesterols, Phospholipids,
Glycolipids et al - As structural components of biological membranes. - Cholesterol serves the precursor of bile salt and
steroid hormones3. Lipid ramification: to involve the different functions
Fatty AcidsAcids obtained by the hydrolysis of fats and oils
• Saturated (have only single bonds)
• Unsaturated (have double bonds)
• Essential -must originate from dietary sources
-the body cannot synthesize
-Polyunsaturated fatty acids
linoleic :(18:2,9,12)
linoleinic:(18:3, 9,12,15)
arachidonic acid :(20:4, 5,8,11,14)
Omega-3 / Omega-6 Fatty AcidsOmega-3 / Omega-6 Fatty Acids
– Sources of omega-3 fatty acid: soybean, salmon……
– Eicosapentaenoic acid(EPA,fish oil): found in oils of shell fish, cold-water tuna, sardines, and sea mammals
• Sources of omega-6 fatty acids– Vegetable oils– Nuts and seeds
Triglycerides ( triacylglycerols ) ,Called “Neutral Fats” - made of 3 free fatty acids and 1 glycerol - FFA 4-22 Carbons long (mostly 16-20) - 95% of dietary lipids (fats & oils)
Triglyceride
Glycerol + 3 FFA TG + H2O
Section 2Digestion of Triacylglycerols
6 Steps of Digestion and absorption of lipids
Minor digestion of triacylglycerols in mouth and stomach by lingual lipase
Major digestion of all lipids in the lumen of the duodenum(十二指肠 ) / jejunum (空肠) by Pancreatic lipases
Bile acid facilitated formation of mixed micelles that present the lipolytic products to the mucosal surface, followed later by enterohepatic (肠肝) bile acid recycling
Passive absorption of the lipolytic products from the mixed micelle into the intestinal epithelial cell , Glycerol & FAs < 12 carbons in length pass thru the cell into the blood without modification. 2-monacylglycerols and FAs > 12 carbons in length are re-synthesized into TGs in the endoplasmic reticulum TGs then form large lipid globules in the ER called nascent chylomicrons (乳糜微粒)” .Several apolipoproteins are required
Re-esterification of 2-monoacylglycerol, lysolecithin (溶血卵磷脂) , and cholesterol with free fatty acids inside the intestinal enterocyte
Assembly and export from intestinal cells to the lymphatics of chylomicrons coated with Apo B48 and containing triacylglycerols, cholesterol esters and phospholipids
Section 3
Metabolism of TAG
1. Synthesis of TAG2. Catabolism of TAG - Fatty acid bata oxidation -Ketogenesis and Ketone Bodies
3. Lipogenesis: Fatty Acid Synthesis4. Some poly-unsaturated FA ramification
The synthesis of TAG1. Mono-acylglycerol pathway (MAG pathway) (for dietary fat digestion and absorption)
pancreatic lipase
FA
pancreatic lipase
FA
ATP,CoA
acyl CoA acyl CoA
intestinal epithelium
intestinal lumen
Chylomicronslymphatic vessels
adipose tissue
CH2OCOR
CHOCOR
CH2OCOR
TAG
CH2OH
CHOCOR
CH2OCOR
DAGCH2OH
CHOCOR
CH2OH
MAG
CH2OH
CHOCOR
CH2OH
MAG
CH2OCOR
CHOCOR
CH2OCOR
TAG
FA FA
2. Diacylglycerol pathway (DAG pathway) (for TAG synthesis of in adipose tissue, liver and kidney)
CH2O-PO3H2
CO
CH2OH
dihydroxyacetone phosphate
liveradipose tissue
NADH+H+NAD+
phosphoglycerol dehydrogenase CH2O-PO3H2
CHOH
CH2OH
3-phosphoglycerol
ADP ATP
glycerol kinase
liverkidney
RCO¡« SCoA
HSCoA
CH2O-PO3H2
CHOH
CH2OCOR
lysophosphatidate
acyl CoA transferase
acyl CoAtransferase
RCO¡« SCoAHSCoA
phosphatidate
CH2O-PO3H2
CHOCOR
CH2OCORH2OPi
CH2OH
CHOCOR
CH2OCOR
diacylglycerol
RCO¡« SCoAHSCoA
acyl CoAtransferase
glucoseCH2OH
CHOH
CH2OH
glycerol
CH2OCOR
CHOCOR
CH2OCOR
triacylglycerol
phosphatase
Catabolism of TAG
Mobilization of triacylglycerols
Mobilization of triacylglycerols:
in the adipose tissue, breaks down triacylglycerols to freefatty acids and glycerol (fattyacids are hydrolyzed initiallyfrom C1or C3 of the fat)
hormone sensitive lipase cleave a fatty acid from atriglyceride, then other lipasecomplete the process of
lipolysis,and fatty acid are released intothe blood by serum albumin
• The glycerol is absorbed by the liver and converted to glycolytic intermediates
Fatty acid bata oxidation
MITOCHONDRION
cell membrane
FA = fatty acidLPL = lipoprotein lipaseFABP = fatty acid binding protein
ACS
FABP
FABPFA
3
FABPacyl-CoA
4
CYTOPLASM
CAPILLARY
LPL
lipoproteins
2
FAFA
1
albuminFA FA
FA
From fat cell
carnitinetransporter
acyl-CoA
5
Overview of fatty acid degradation
ACS = acyl CoA synthetase
acetyl-CoA TCAcycle
-oxidation6
7
Steps in Beta Oxidation
• Fatty Acid Activation by esterification with CoASH
• Membrane Transport of Fatty Acyl CoA Esters
• ***Carbon Backbone Reaction Sequence• Dehydrogenation
• Hydration
• Dehydrogenation
• Thiolase Reaction (Carbon-Carbon Cleavage)
• Acyl CoA synthetase reaction occurs on the mitochondrial membrane
1. Activation of Fatty Acids
• Carnitine carries long-chain activated fatty acids into the mitochondrial matrix
2.Transport into Mitochondrial Matrix
• Carnitine carries long-chain activated fatty acids into the mitochondrial matrix
• Each round in fatty acid degradation involves four reactions– 1. oxidation totrans-∆2-Enoly-CoARemoves H atoms from the and carbons-Forms a trans C=C bond-Reduces FAD to FADH2
3. Fatty acid Beta oxidation
2. Hydration to L–3–Hydroxylacyl CoA– Adds water across the
trans C=C bond
– Forms a hydroxyl group (—OH) on the carbon
3. Oxidation to– 3–Ketoacyl CoA
– Oxidizes the hydroxyl group
– Forms a keto group on the carbon
4. Thiolysis to produce
Acetyl–CoA
– acetyl CoA is cleaved:By
splitting the bond between the
and carbons.
– To form a shortened fatty acyl
CoA that repeats steps 1 - 4 of
-oxidation
-Oxidation of Myristic(C14) Acid
-Oxidation of Myristic (C14) Acid
7 Acetyl CoA
6 cycles
Cycles of -Oxidation
The length of a fatty acid• Determines the number of oxidations and the
total number of acetyl CoA groups
Carbons in Acetyl CoA -Oxidation CyclesFatty Acid (C/2) (C/2 –1)12 6 514 7 616 8 718 9 8
-Oxidation and ATP
Activation of a fatty acid requires:
2 ATP
One cycle of oxidation of a fatty acid produces:
1 NADH 3 ATP
1 FADH2 2 ATP
Acetyl CoA entering the citric acid cycle produces:
1 Acetyl CoA 12 ATP
ATP for Myristic Acid C14
ATP production for Myristic(14 carbons):Activation of myristic acid -2 ATP
7 Acetyl CoA7 acetyl CoA x 12 ATP/acetyl CoA 84 ATP
6 Oxidation cycles 6 NADH x 3ATP/NADH 18 ATP6 FADH2 x 2ATP/FADH2 12 ATP
Total 102 ATP
Oxidation of Special Cases (monounsaturated fatty acids)
Odd Carbon Fatty Acids
CH3CH2CH2--CH2CH2--CH2CH2--CH2CH2--CH2CH2--CH2COSCoA
5 Cycles
5 CH3COSCoA + CH3CH2COSCoA
Propionyl CoA
CO2H
COSCoA
H-C-CH3
CO2H
COSCoA
CH3-C-HHO2CCH 2CH2COSCoA
D-MethylmalonylCoA
L-MethylmalonylCoA
Succinyl CoA
TCA Cycle
Propionyl CoA CarboxylaseATP/CO2
EpimeraseMutase
Vit. B12
Ketogenesis (Ketosis):
formation of Ketone Bodies *****
2 CH3COSCoA CH3COCH2COSCoAThiolase
CH3COSCoA
Acetoacetyl CoA
HO2C-CH2-C-CH2COSCoA
OH
CH3
-Hydroxy--methylglutaryl CoA(HMG CoA)
HMG CoASynthase
Cholesterol(in cytosol)
Severalsteps
Ketogenesis(in liver: mitochon-
drial matrix)
Ketogenesis: formation of Ketone Bodies
HO2C-CH2-C-CH2COSCoA
OH
CH3
HMG CoA
CH3COCH2CO2H
Acetoacetic Acid
HMG CoAlyase
- CH3COSCoA
- CO2
CH3COCH3
Acetone(volatile)
CH3CHCH2CO2H
OH
-Hydroxybutyrate
NADH + H+
NAD+Dehydrogenase
Ketone bodies are important sources of energy, especially in starvation
Acetoacetate-Hydroxybutyrate
-Hydroxybutyrate dehydrogenase
NAD+NADH
CitricAcidCycle
2 Acetyl CoA
CoA
ThiolaseAcetoacetyl CoA
Succinyl CoA
Succinate
CoA transferase
Oxidation of ketone bodies in brain, muscle, kidney, and intestine
Succinyl CoA synthetase = loss of GTP
The significance of ketogenesis and ketogenolysis
• Ketone bodies are water soluble, they are convenient to transport in blood, and readily taken up by non-hepatic tissues
In the early stages of fasting, the use of ketone bodies by heart, skeletal muscle conserves glucose for support of central nervous system. With more prolonged starvation, brain can take up more ketone bodies to spare glucose consumption
• High concentration of ketone bodies can induce ketonemia and ketonuria, and even ketosis and acidosis
When carbohydrate catabolism is blocked by a disease of diabetes mellitus or defect of sugar source, the blood concentration of ketone bodies may increase,the patient may suffer from ketosis and acidosis
TCA
extrahepatic tissues
CO2 + H2O + energy¢Ü
Overview Catabolism of TAG
TAG¢Ù FFAs
glycerol
¦Â-oxidation¢Ú
acetyl CoA
not in adipose tissue and muscle glycolysis
¢Ý
¢Û in liver
Ketone bodies
• Fatty acid are synthesized and degraded by different pathways
– from acetyl CoA
– in the cytosol
– intermediates are attached to the acyl carrier protein (ACP)
– the activated donor is malonyl–ACP
– reduction uses NADPH + H+
– stops at C16
(palmitic acid 软脂酸 )
Lipogenesis: Fatty Acid Synthesis
Reactivity of Coenzyme A
NucleoNucleophilic acyl substitutionphilic acyl substitution
CHCH33CCSCoASCoA
OOHYHY••••
CHCH33CC
OO
YY •••• ++ HHSCoASCoA
Acetyl coenzyme A is a source of an acetyl group toward biological nucleophiles(it is an acetyl transfer agent)
Reactivity of Coenzyme A
can react via enol(can react via enol(烯醇 ))
CHCH33CCSCoASCoA
OO
Acetyl coenzyme A reacts with biological electrophiles at its carbon atom
CCSCoASCoA
OHOH
HH22CC
EE++
CHCH22CCSCoASCoA
OO
EE
Formation of malonyl–CoA is the committed step in fatty acid synthesis
Formation of Malonyl Coenzyme A
O || CH3—C—S—CoA + HCO3
- + ATP
Acetyl CoA O O || ||
-O—C—CH2—C—S—ACP + ADP + PiMalonyl (丙二酰 ) CoA
• The intermediates(acetyl-ACP and malonyl-ACP) in fatty acid synthesis are covalently linked to the acyl carrier protein (ACP)
Formation of Acetyl and Malonyl ACP
In bacteria the enzymes that are involved in elongation are separate proteins
In higher organisms the activities all reside on the same polypeptide– To start an elongation cycle, Acetyl–CoA and Malonyl–CoA
are each transferred to an acyl carrier protein
O ||CH3—C—S—ACP ( Acetyl-ACP)
O O || ||
-O—C—CH2—C—S—ACP (Malonyl-ACP)
Condensation and Reduction
In reactions 1 and 2 of fatty acid synthesis:
• Condensation by a synthase combines acetyl-ACP with malonyl-ACP to form acetoacetyl-ACP (4C) and CO2 (reaction 1)
• Reduction converts a ketone to an alcohol using NADPH (reaction 2)
Dehydration and Reduction
In reactions 3 and 4 of fatty acid synthesis:
• Dehydration forms a trans double bond (reaction 3)
• Reduction converts the double bond to a single bond using NADPH (Reaction 4)
Lipogenesis Cycle Repeats
Fatty acid synthesis continues:
• Malonyl-ACP combines with the four-carbon butyryl-ACP to form a six-carbon-ACP.
• The carbon chain lengthens by two carbons each cycle
Lipogenesis Cycle Completed
• Fatty acid synthesis is completed when palmitoyl ACP reacts with water to give palmitate (C16)
and free ACP.
Summary of Lipogenesis
• Endoplasmic reticulum( 内质网 ) systems introduce double bonds into long chain acyl–CoA's
– Reaction combines both NADH and the acyl–CoA's to reduce O
2 to H
2O
Elongation and Unsaturation
• convert palmitoyl–CoA to other fatty acids
– Reactions occur on the cytosolic face of the endoplasmic reticulum.
– Malonyl–CoA is the donor in elongation reactions
Oxidation and Fatty Acid Synthesis
Fatty Acid Formation
• Shorter fatty acids undergo fewer cycles • Longer fatty acids are produced from palmitate
using special enzymes• Unsaturated cis bonds are incorporated into a 10-
carbon fatty acid that is elongated further• When blood glucose is high, insulin stimulates
glycolysis and pyruvate oxidation to obtain acetyl CoA to form fatty acids
• The stoichiometry of palmitate synthesis:– Synythesis of palmitate from Malonyl–CoA
– Synthesis of Malonyl–CoA from Acetyl–CoA
– Overall synthesis
Stoichiometry of FA synthesis
• The malate dehydrogenase and NADP+–linked malate enzyme reactions of the citrate shuttle exchange NADH for NADPH
Sources of NADPH
• Acetyl–CoA is synthesized in the mitochondrial matrix, whereas fatty acids are synthesized in the cytosol– Acetyl–CoA units are shuttled out of the mitochondrial matrix as citrate:
Citrate Shuttle
• Regulation of Acetyl carboxylase (乙酰羧化酶)– Global
( + ) insulin
( - ) glucagon
( - ) epinephrine
– Local( + ) Citrate
( - ) Palmitoyl–CoA
( - ) AMP
Regulation of Fatty Acid Synthesis
• Eicosanoid horomones are synthesized from arachadonic acid (20:4,二十碳 - 四烯酸 )
– Prostaglandins (前列腺素)• 20-carbon fatty acid containing 5-carbon ring
• Prostacyclins• Thromboxanes(血栓噁烷)
– Leukotrienes (白三烯)• contain three conjugated double bonds
Eicosanoid Hormones (花生四烯酸类激素)
Eicosanoid Hormones
Eicosanoid Hormones
Section 4
Metabolism of phospholipids(磷脂)
PhospholipidsPhospholipids• Structure
– Glycerol + 2 fatty acids + phosphate group
• Functions– Component of cell
membranes– Lipid transport as part of
lipoproteins• Food sources
– Egg yolks, liver, soybeans, peanuts
Phospholipids
• Phospholipids are intermediates in the biosynthesis of triacylglycerols
• The starting materials are glycerol 3-phosphate and the appropriate acyl coenzyme A molecules
Biosynthesis of glycerophospholipids1. DAG shunt is the major pathway for biosynthesis of phosphatidyl choline (lecithin) and phosphatidyl ethanolamine (cephalin)
HO-CH2-CH-COOH
NH2serine
CO2
HO-CH2-CH2-NH2ethanolamine
3(S-adenosylmethionine)HO-CH2-CH2-N(CH3)3
+
cholineATP
ADPkinase ATP
ADPkinase
P -O-CH2-CH2-NH2
phosphoethanolamine P -O-CH2-CH2-N(CH3)3
+
phosphocholineCTP
PPi
cytidyl transferase CTP
PPi
cytidyl transferase
CDP-O-CH2-CH2-NH2CDP-ethanolamine CDP -O-CH2-CH2-N(CH3)3
CDP-choline
phosphatidyl ethanolamine (PE) phosphatidyl choline (PC)
H2C
C
H2C
O C R1
O
HOC
O
R2
OH
DAG
CMP CMP
diacylglycerol transferase
CDP-DAG shunt
CMP
glucose
glycerol 3-phosphate2 acyl CoA
2 CoA
CTP
PPi
phosphatidyl serine
inositol
phosphatidyl inositol
phosphatidyl glycerol
diphosphatidyl glycerol (cardiolipin)
CMP
CMP
serine
Phosphatidic acid
2. CDP-DAG shunt is the major pathway for the synthesis of phosphatidyl serine, phosphatidyl inositol and cardiolipin - in this pathway, DAG is activated as the form of CDP-DAG
Cardiolipin (diphosphatidylglycerol)
C
O
O CHR2
CH2 O C
O
R1
CH2 O P
O
O-
O CH2
P
O
O-
O
CH2
CH
CH2
O C
O
R3
O C
O
R4
C
H2C
HO H
O
CDP-diacylglycerol
Degradation of glycerophospholipids
H2C
C
H2C
O C R1
O
HOC
O
R2
O P O
O
O
X_
H2O
H2O
H2O
H2O H2O
H2O
O P O
O
O
X_
_
H2C
C
H2C
O C R1
O
HOC
O
R2
OH
diglyceride
phospholipase C
XOH
H2C
C
H2C
O C R1
O
HOC
O
R2
O P OH
O
O_
phosphatidic acid
phospholipase D
glycerophospholipid
OHC
O
R1
phospholipase A1
H2C
C
H2C
OH
HOC
O
R2
O P O
O
O
X_
lysophospholipid 2
phospholipase B2OHC
O
R2
H2C
C
H2C
OH
HHO
O P O
O
O
X_
phospholipase A2
OHC
O
R2 H2C
C
H2C
O C R1
O
HHO
O P O
O
O
X_
lysophospholipid 1
OHC
O
R1
phospholipase B1
(glycerophophocholine)
Metabolism of sphingolipids
x = monosaccharide cerebrosidex = sulfated galactose ( = cerebroside sulfate) sulfatide
x = oligosaccharide globoside
x = oligosaccharide + sialic acid ganglioside
note: sialic acid = N-acetylneuraminic acid
Sphingolipids are a class of
lipids containing sphingosine
instead of glycerol
include: glycosphingolipids
phosphosphingolipids
脑苷脂
神经节苷脂
硫酸脑苷脂
红细胞糖苷脂
唾液酸 N-乙酰神经氨酸
The structure of phosphosphingolipids
The structure of glycosphosphingolipids
P
fatty acidR
鞘氨醇 phosphate cholinesphingosine
H3C ( CH2)1 2 C H C H C H C H C H2 O
O H N H
C O
O
O
O
C H2 CH2
N
(CH3)3+
sphingosine
fatty acid
H3C (CH2)1 2 C H C H C H C H C H2 O X
O H N H
C O
R
sugar
Section 5
Metabolism of cholesterol
Structure of Cholesterol
HOHO
CHCH33
HH
HH
HH
CHCH33
CHCH33 CHCH33
CHCH33
Fundamental framework of steroidsFundamental framework of steroids
Structure of CholesterolStructure of Cholesterol
A B
C D1
2
34 5
6
7
89
10
1112
13
14 15
16
1718
19
Cholesterol Biosynthesis 1. Formation of Mevalonate
2 CH3COSCoA CH3COCH2COSCoAThiolase
CH3COSCoA
Acetoacetyl CoA
HO2C-CH2-C-CH2COSCoA
OH
CH3
-Hydroxy-bata-methyl-glutaryl CoA (HMG CoA)
HMG CoASynthase
HO2C-CH2-C-CH2CH2OH
OH
CH3
3R-Mevalonic acid
甲羟戊酸
HMGCoAreductase
CoASH NADP + NADPH + H+
Key control step
Liver is primary site of cholesterol biosynthesis
Cholesterol Biosynthesis 2. processing of Squalene
-O2C-CH2-C-CH2CH2OH
OH
CH3
Mevalonate
-O2C-CH2-C-CH2CH2OPOP
CH3
OH
2 Steps
ATP
5-Pyrophospho(焦磷酸 )-mevalonate
CH2=C-CH2CH2OPOP
CH3
- CO2
- H2O
Isopentenyl(异戊烯 )pyrophosphate
CH3-C=CH2CH2OPOP
CH3
Dimethylallylpyrophosphate
Isomerase
Isoprenoid (异戊二烯)Condensation
H
OPOP
OPOP
Head
TailHead
Tail
IsopentenylPyrophosphate (IPP)
Dimethylallylpyrophosphate Head to tail
Condensation
OPOP
Geranyl ( 牛龙牛儿基 ) Pyrophosphate (GPP)
OPOP
Farnesyl(法尼基)Pyrophosphate (FPP)
Head to tailcondensationof IPP and GPP
Tail to tailcondensationof 2 FPPs
Squalene鲨烯
Head Tail
Head Tail
Isoprenes异戊二烯
3. Conversion of Squalene to Cholesterol
O
H +
CH3H3C
CH3
HO
CH3
CH3
CH3
HO
CH3
Squalene鲨烯
Squalenemonooxygenase
2,3-Oxidosqualene:lanosterol cyclase
Lanosterol羊毛固醇
20 Steps
Cholesterol
O2
Squalene-2,3-epoxide
Transformations of Cholesterol
Cholesterol is the biosynthetic precursor to a large number of important steroids:
Bile acidsVitamin D3CorticosteroidsSex hormones
Section 6
Lipoproteins metabolism
General Features of Lipoproteins Apolipoproteins: specific lipid-binding proteins that attach to the surface
intracellular recognition for exocytosis of the nascent particle after synthesis
activation of lipid-processing enzymes in the bloodstream, binding to cell surface receptors for endocytosis and clearance
Main lipid components: triacylglycerols, cholesterol esters, phospholipids. Major lipoproteins:
chylomicronsvery low density lipoproteins (VLDL)low density lipoproteins (LDL) high density lipoproteins (HDL)
Subfraction: intermediate density lipoproteins (IDL)
Electrophoretic mobility (charge):HDLs = lipoproteinsLDLs = -lipoproteinsVLDLs = pre- lipoproteins (intermediate between and mobility)
_
_origin ¦Ã ¦Â ¦Á2 ¦Á1 A
CM pre ¦Â ¦Á ¦Â
Plasma lipoproteins
Model of low density lipoprotein. Other lipoproteins have a similar structure differing in the core content of lipid and the type of apoproteins on the surface of the molecule
Functions of apolipoproteins
Protein (Enzyme)
Site of Action
Activator Function
LPL (Enzyme)capillary
wallsapo CII
excises FFA from TAGs in chylomicrons and VLDLs for adipose and muscle
CERPplasma
membrane
apo A1 (choles.Induced)
flips cholesterol (and lecithin) to outer layer of lipid bilayer for LCAT action in blood
Apo A1blood, plasma
membranenone
activates LCAT and CERP; binds to apo A1 receptors on cells requiring cholesterol
extraction
Apo B48 Gut none export of chylomicrons from intestinal cells
Apo B100 Various cells noneligand for LDL receptor; export of liver
VLDL
Apo CIIcapillary
wallsnone activates lipoprotein lipase
Apo E liver nonereceptor ligand - clears remnants, IDL, and
HDL
Lipoprotein classes
Total protein (%)
Total lipids (%)
Percent composition of lipid fractionsPL ChE Ch TAG
CM 1.5-2.5 97-99 7-9 3-5 1-3 84-98(B,C-III,II,I)
VLDL 5-10(B,C-III,II,I)
90-95 15-20 10-15 5-10 50-65
LDL 20-25(B)
75-80 15-20 35-40 7-10 7-10
HDL 40-45(A-I)
55 35 4 512
composition of lipoproteins
liver
ApoB48 aids with chylomicron assembly
Lymph system:Chylomicrons to capillaries via lymph
inte
stin
e non-hepatic tissuesnon-hepatic tissues
C E C EC EC E C E
C EC E C E
C E
Chylomicrons carry dietary fatty acids to tissues
Nascent chylo-microns acquire apo CII (C) and E (E) from HDL
chylomicron interacts with lipoprotein lipase removing FFA
Chylomicron (or VLDL)
Apo CII
Lipoprotein lipase
Polysaccharide Chain
EndothelialSurface of cell
Triacylglycerolin core
Free fatty acids
Glycerol
To Liver
Free fatty acidsIn cellulo (muscle & adipose)
Capillary
Lipoprotein lipase action on chylomicron triacylglycerol
(an identical reaction occurs with VLDL)
LIVER
ApoB48chylomicron remnants lose CII to HDL
non-hepatic tissuesnon-hepatic tissues
C E C E
E
E
E
EC
C
C
C EC E C E
C E
EE E
Liver: apo E receptor takes up remnants to deliver cholesterol
Exogenous pathway of lipid transportChylomicrons carry dietary fatty acids to tissues and the remnants take cholesterol to the liver
Lymph system:
C E C EC E
chylomicron acquires apo CII (C) and E (E) from HDL
chylomicron interacts with lipoprotein lipase removing FFA
B100 (B) helps assemble and export nascent VLDL
LIVER
nascent VLDL acquires apo CII (C) and apo E (E) from HDL
C EC E C E C EC E C EC E
C EC E
B B
B
BB
B BB
bile acids
HDL scavenge
cholesterol
C EC E
B BB
The liver-directed endogenous pathway of lipoprotein metabolism
non-hepatic tissuesnon-hepatic tissues
LPL hydrolyze TAGs; FFA uptake; LDL circulate to tissues
apo B100 on LDL bind to receptor
LDL taken into the cell to deliver cholesterol
CII and E release to HDL
Apo E binds liver receptor
Cholesterol uptake; excreted as bile acids
Nascent Chylomicron Assembly in Gut Mediated by B48
Nascent HDL Assembled in liver Loans apo E/ apo CII
to nascent chylomicrons
Mature Chylomicron Apo E and CII
added from HDL
Lipoprotein Lipase capillary walls hydrolyzes TAG deliver FFA into adipose/muscle
Mature HDL CE from peripheral cells
activated by apo A1 Apo CII returned by
chylomicrons
Chylomicron Remnant from mature chylomicron apo CII returned to HDL
Chylomicrons: Exogenous Pathway
HDL: Both Pathways
apo CII
Triacylglycerol Cholesterol ester
Phospholipid
E
CII A1
E B48 CII
A1
E
CII
B48
apo E & CII from HDL
B48
adipose &muscleFFA
CII
CII
CII
CII
E
EE
E
CII
CII
Chylomicron Processing and Interface with HDL
Mature Chylomicron Apo E and CII
added from HDL CII activates LPL
B48
Lipoprotein Lipase capillary walls hydrolyzes TAG deliver FFA into adipose/muscle
LDL from mature VLDL
A1
CII
B100
Nascent VLDL Assembly in Liver Mediated by B100
VLDL/LDL: Endogenous Pathway
HDL: Both Pathways
E
CIIA1
VLDL/LDL Processing and Interface with HDL
Mature VLDL Apo E and CII
added from HDLE
CII
B100
apo CII & E from HDL
EE
E
E
CII
CII
CII
adipose &muscle FFA
apo CII + EE
CII
EEE
CII
CII
Mature HDLApo CII/E returned by VLDL
B100
B100
Mature VLDL Apo E and CII
added from HDL CII activates LPL
E Receptor
Mature HDL
CE Metabolism Bile acids
Chylomicron Remnant
E Receptor
B100receptor
LDL
Clearance of Cholesterol by Liver from Chylomicron Remnants, HDL and LDL
E
B48
E
B48
E
B48
A1
EA1
E
A1
E
B100
B100
B100
Oxidized LDL
1. Uptake by "scavenger receptors" on
macrophages that invade artery walls;
become foam cells
2. Elicits CE deposition in artery walls
Consequence of Oxidized LDL Formation
Oxidation of LDL
LDL
Atherosclerosis动脉粥样硬化
free pool ofcholesterol
LDLCE
endocytosis
late endosome
ACEHCE cholesterol
Cholesterol Esterase
Cholesterol metabolism to bile acids or steroids
Golgi
Cholesterol release for transport to liver
MembraneCholesterol
ACAT (stimulated by cholesterol)
CE CE
CE stored in droplets
CERPL C A T
Apo A1 receptor
A1
CII
EA1
ECIICE in nascent HDL
Apo A1 binds to receptor, activates CERP to pump out cholesterol, and LCAT to esterify cholesterol
Mature HDL:Cleared by liver
LDL receptor sorting endosome:
ligand/receptor dissociationlysosome
Reverse CholesterolTransport
Lipoprotein classesLipo-
protein Source Apo ProteinsProtein:Lipid/
Major (minor) Lipid Transported
Function
Chylo-microns gut B48, CII*, E* 1:49triacylglycerol (CE)
Dietary:FFA Adipose/muscleCE Liver via remnants
VLDL liver B100, CII*, E* 1:9 triacylglycerol (CE)Synthesized:FFA adipose/muscleCE LDL
LDL blood B100 1:3 cholesterol ester CE to liver (70%) and peripheral cells (30%)
HDL liver A1, CII, E("ACE")
1:1 cholesterol estersupplies apo CII, E to chylomicrons and VLDL; mediates reverse cholesterol transport
hypercholesterolemia
家族性高胆固醇血症表现
Guidelines for Appropriate Intake of Fat
☻ reduce fat in diet to <30%
☻ avoid saturated fat (animal fat)
☻ avoid margarine(奶油) , baked goods, fried food
☻ mono/polyunsaturated cooking oils are best (olive, corn)
☻ eat foods rich in -3 polyunsaturated fatty acids
(e.g, soybean , salmon)
选择题练习脂代谢
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
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
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
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
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
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
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
8. 下列关于HMG-CoA还原酶的叙述哪项事错误的 ( )
A 此酶存在于细胞胞液中
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
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
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
11. The organ having the strongest ability of fatty acid synthesis is ( )
A fatty tissue
B lacteal gland
C liver
D kidney
E brain
12. Which one transports cholesterol from outer to inner of liver?
A CM
B VLDL
C LDL
D HDL
E IDL
13. Which one is essential fatty acid?
A palmitic acid
B stearic acid
C oleinic acid
D octadecadienoic acid
E eicosanoic acid
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
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
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
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)
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
19. Which can be the source of acetyl CoA?
A glucose
B fatty acid
C ketone body
D cholesterol
E citric acid
20. The matters which join in synthesis of cholesterol directly are ( )
A acetyl CoA
B malonyl CoA
C ATP
D NADH
E NADPH