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ن ف معا اسمى ال علمهيا نى امع عالمالحرية
تمنحها ال الخيرية الحرية البر هيئاتينمو نبت وزكية الحرية حرة بدماء
به واحترق فيه وانغمس واحد، عمل على اهتمامك رك,ز
. . مبدعا لتكن وأعشقه
،العقل وتقدح الرجال، تصقل فإنها بالمحن ذرعا. تضق ال
. الهمم وتشعل
والفاشل صفر، والعاطل يحسن، ما امرئٍ كل قيمة. رخيص والمخفق ممقوت،
II- α-Oxidation:• This types of oxidation occurs in α position and
characterized by:1- It is mechanism mainly for branched chain fatty
acid, which is methylated at β position.2- It is specific for oxidation of phytanic acid.3- It is minor pathway for fatty acid oxidation.4- It occurs mainly in brain and nervous tissues.• In α-oxidation, there is one carbon atom removed
at a time from α position.• It dose not require CoASH and dose not generate
high energy phosphate.
64
R - CH2 - CH - CH2 - COOH R - CH2 - CH - CH - COOH
CH3
[O]
HydroxylaseCH3 OH
-hydroxyadd
R - CH2 - CH - C - COOH
CH3 O-keto acid
2H
Dehydrogenase
R - CH2 - CH - COOH
CH3
Lower chain F.A.
Oxidativedecarboxylation
CO2 [O]
Propionyl ~ CoA + Acyl ~ CoA -Oxidation-Oxidation
Refsum’s disease:1- This is inherited deficiency of enzymes responsible for α-oxidation of phytanic acid. This leads to accumulation of phytanic acid in serum and nervous tissue and produce nervous damage e.g. deafness and blindness.
65
ω-Oxidation
1. It is oxidation of terminal CH3 group of fatty acid.
2. It produces dicarboxylic fatty acids. By β-oxidation, they are converted to adipic acid (6 carbons) and suberic acid (8 carbons).
3. It is a minor pathway for fatty acid oxidation and used for oxidation of long chain fatty acids.
3. overproduced during fasting or in untreated diabetes mellitus.
69
Types
1-
2-
3-
70
The formation of ketone bodies (Ketogenesis)
Location: hepatic mitochondria
Material: acetyl CoA
Rate-limiting enzyme: HMG-CoA synthase
71
72
Utilization of ketone bodies (ketolysis) Occurs at extrahepatic tissues
Succinyl-CoA transsulfurase
73
HSCoAATP
AMP PPi
Acetoacetate thiokinase
-
Occurs at extrahepatic tissues due toLack of succinyl-CoA transsulfurase and Acetoacetate thiokinase in the liver.
74
The significance of ketone bodies
• 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
75
Glucose Glucose exported as fuel for tissues such as brain
oxaloacetate
Fattyacids Acetyl-CoA
β-oxidation
gluconeogenesis
CitricAcid cycle
Ketone bodiesexported as energy source for heart, skeletal muscle, kidney, and brain
Ketone body formation
Hepatocyte
Acetoacetate, β-hydroxybutyrate,
acetone
CoA
76
Ketosis consists of ketonemia, ketonuria and smell of acetone in breath
77
Causes for ketosis
• Severe diabetes mellitus
• Starvation
• Hyperemesis (vomiting) in early pregnancy
78
CH3COCH2CO2H pKa = 3.6 Acetoacetic Acid
CH3CHCH2CO2H pKa = 4.7 -Hydroxybutyric acid
OH
Concentration of acetoacetic acid can result in metabolic acidosis affinity of Hb for O2 coma death
Metabolic Acidosis in Untreated Diabetes Mellitus
Lipogenesis
8080
A- Definition:
- Lipogenesis is the synthesis of triacylglycerol from fatty acids (acyl CoA) and glycerol (glycerol-3-phosphate).
B- Steps:
1- Activation of fatty acids into acyl CoA:
81
2- Synthesis of glycerol-3- phosphate:
82
3-Formation of TAG
8383
Regulation of lipogenesis
After meal, lipogenesis is stimulated:
- Insulin is secreted which stimulates glycolysis. Glycolysis supplies
dihydroxyacetone phosphate that converted into glycerol-3-phosphate
in adipose tissue, so lipogenesis is stimulated.
During fasting lipogenesis is inhibited:
- Anti-insulin hormones are secreted. These inhibit lipogenesis and
stimulate lipolysis
84
Fatty Acid Biosynthesis
85
1. Cytoplasmic or extramitochonderial (de novo)
synthesis
2. Microsomal pathway (aerobic elongation
pathway & ∆9 Unsaturation)
3. Mitochondrial (anaerobic elongation )
86
1. Palmitic Acid Synthesis
• Location: cytosol of liver,lactating mammary glands and adipose tissue. Precursor: acetyl CoA
• Other materials: ATP, NADPH, CO2
• Main product is palmitate (C16)• Problem:
» Most acetyl CoA produced in mitochondria» Acetyl CoA unable to traverse mitochondrial
Differences in the oxidation and synthesis of FAs β-oxidation Fatty acid synthesis
Site Mitochondria Cytoplasm
Intermediates Present as CoA derivatives
Covalently linked to SH group of ACP
Enzymes Present as independent proteins
Multi-enzyme complex
Sequential units
2 carbon units split off as acetyl CoA
2 carbon units added, as 3 carbon malonyl CoA
Co-enzymes NAD+ and FAD are reduced
NADPH used as reducing power
105
Routes of synthesis of other fatty acids
106
2. Elongation of palmitate
Elongation beyond the 16-C length of the palmitate occurs in mitochondria and endoplasmic reticulum (ER).
107
Fatty acid elongation within mitochondria uses the acetyl-CoA as donor of 2-carbon units and NADPH serves as electron donor for the final reduction step.
Fatty acids esterified to coenzyme A are substrates for the ER elongation machinery, which uses malonyl-CoA as donor of 2-carbon units.
108
3. The synthesis of unsaturated fatty acid
• Formation of a double bond in a fatty acid involves several endoplasmic reticulum membrane proteins in mammalian cells
109
Desaturases introduce double bonds at specific positions in a fatty acid chain.
110
Orlistat: A Fatty Acid Synthase (FAS) Inhibitor
Anti-obesity (Inhibitspancreatic lipase in GIT)
Inhibits thioesterase domain of FAS
Anti-cancer (experimental): FAS overexpressed in several tumor types; inhibition induces apoptosis
Metabolism of phospholipids
112
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
113
• Phospholipid refers to phosphorous-containing lipids.
Phospholipids
Glycerophospholipids
Sphingolipids
114
Phospholipids
Glycerol as alcoholSphingosine as
alcohol
SphingomyelineNon nitogenous base Nitrogenous base
Cephalin
Lecithin
Lipositol2nd messenger
Phosphatidic acid
Cardiolipin2phosphatidic acidLiked by glycerol
Phosphatidyl serine
Lysophospholipid
Plasmalogen
115
Classification and Structure of Glycerophospholipids
• Glycerophospholipids are lipids with a glycerol, fatty acids, a phosphate group and a nitrogenous base.
116
Phosphatidylcholine
fatty acids
nitrogenous base
glycerol
117
CH2 O
C H
CH2
O
O
C
C
P
R1
R2
O
O
O
O
OH
X
甘油
脂酰基
脂酰基
含氮化合物
The basic structure of glycerophospholipid
glycerolfatty acyl group
Nitrogenous basefatty acyl group
118
In general, glycerophospholipids contain a saturated fatty acid at C-1 and an unsaturated fatty acid (usually arachidonic acid) at C-2.
119
Some common glycerophospholipid
120
Some common glycerophospholipid (continue)
121
Synthesis of Glycerophospholipid
Location:
All tissue of body, especially liver & kidney
Endoplasmic reticulum
Pathways:
1- CDP-diacylglycerol pathway
2- Diacylglycerol pathway
122
a. FA Glycerol
b. poly unsaturated fatty acid from plant oil c. choline ethanolamine serine inositol
d. ATP, CTP
e. Enzymes and cofactors
The system of synthesis
from carbohydrate
from food or synthesis in body
123
Diacylglycerol pathway
SerineEthanolamine
CO2
ATP
ADP
CTP
PPi
DG
CMPCO2
ATP
ADP
CTP
PPi
DG
CMP
3 SAMHO CH2 CH
NH2
COOH HO CH2 CH2 NH2 HO CH2 CH2 N(CH3)3
Choline
PhosphoethanolamineO CH2 CH2 NH2P O CH2 CH2 N(CH3)3
CDP
P
Phosphocholine
CDP-ethanolamineO CH2 CH2 NH2 O CH2 CH2 N(CH3)3CDP
Lysophospholipids, the products of Phospholipase A hydrolysis, are powerful detergents.
CH2
C HO
CH2O
O C R1
O
P O
O
O
X
H2O
CR2
OOCR2
O
CH2
C HHO
CH2O
O C R1
O
P O
O
O
X
Lysophospholipidphospholipid
PLA2
128
Metabolism of sphingolipids
• Palmitic acid + serine Called Sphingosine
• Sphingosine + Fatty acid Called ceramide
• Ceramide + Choline Called Sphingomylein
129
130
131
Respiratory Distress Syndrome
Most frequently seen in premature infants
Also called hyaline membrane disease
Failure to produce sufficient dipalmitoyl phosphatidylcholine,which normally is found in the extracellular fluid surroundingalveoli; decreases surface tension of fluid to prevent lung collapse
Treatment in infants born before 30 weeks includes
administration of artificial lung surfactant (e.g., Exosurf orPumactant)
132
Glycolipids
133
Ceramide Cerebroside
Sulphatides Gangliosides
Sulphate+ one or more of sialic acid (eg NANA or N acetyl galactos amine
Ceramide - O - Glucose - Galactose - N-Acetylgalactose
Hexoseaminidase Acatalyzes cleavage of this glycoside linkage
GM2 (a ganglioside):
Autosomal recessive disorder characterized by deficiencyof hexoseaminidase A; accumulation of gangliosides in brainMost prevalent in Jews from Eastern EuropeFor further information see: http://www.marchofdimes.com/professionals/681_1227.asp
137
Other Gangliosidoses
Gaucher’s disease:
Fabry’s disease:
Nieman-Pick disease:
Ceramide - O - Glucose
Ceramide - O - Glucose - O - Galactose - O - Galactose
Ceramide - Phosphate - Choline
-glucosidase
-galactosidase
sphingomyelinase
138
• Eicosanoid horomones are synthesized from arachadonic acid (20:4)– Prostaglandins
• 20-carbon fatty acid containing 5-carbon ring
• Prostacyclins
• Thromboxanes
– Leukotrienes• contain three conjugated double bonds
Eicosanoid Hormones
139
Eicosanoid Hormones
140
Cholesterol MetabolismCholesterol Metabolism
141
Structure and function of cholesterol
1. Function of cholesterol:
(1) It is a constituent of all cell membranes.
(2) It is necessary for the synthesis of all steroid hormones, bile salts and vitamin D.
142
2. Structure of cholesterol
All steroids have cyclopentano penhydro phenanthrene ring system.
CH3
CH3
HO
H3C CH3
CH3
A B
C D
12
34
56
7
89
10
1112
13
14 15
1617
18
19
20
2122 23 24 25
26
27
143
Cholesterol ester
OCR
O
144
Synthesis of cholesterolLocation:
• All tissue except brain and mature red blood cells.
• The major organ is liver (80%).
• Enzymes locate in cytosol and endoplasmic reticulum.
Materials:
Acetyl CoA, NADPH(H+), ATP
145
Acetyl-CoA is the direct and the only carbon source.
146HMG CoA reductase is the rate-limiting enzyme
Acetoacetyl-CoA
Acetyl-CoAHMG-CoA
147The total process of cholesterol de novo synthesis
148
Regulation of cholesterol synthesis
MVAHMG CoA reductase
cholesterol
bile acid
fasting Glucagon
after meal insulin thyroxine
HMG CoA
149
Transformation and excretion of cholesterol
Steroidhormones
Bile acids
Cholesterol
Vitamin D
150
1. Conversion of Cholesterol into bile acid
(1) Classification of bile acids
The primary bile acids are synthesized in the liver from cholesterol. The 7-hydroxylase is rate-limiting enzyme in the pathway for synthesis of the bile acids.
151
The secondary bile acids are products that the primary bile acids in the intestine are subjected to some further changes by the activity of the intestinal bacteria.
152
Classification of bile acids
Classification Free bile
acidsConjugated bile acids
Primary bile acids
Cholic acidGlycocholic
acidTaurocholic acid
Chenodeoxy-cholic acid
Glycocheno-deoxycholic
acid
Taurocheno-deoxycholic acid
Secondary bile acids
Deoxycholic acid
Glycodeoxy-cholic acid
Taurodeoxy-cholic acid
Lithocholic acid
Glycolitho-cholic acid
Taurolitho-cholic acid
153
(2) Strcture of bile acids
HO OH
OH
H
COOH
HO OH
OH
H
CONHCH2COOH
HO OHH
COOH
HO OH
OH
H
CONHCH2CH2SO3H
cholic acid chenodeoxycholic acid
glycocholic acid taurocholic acid
3 7
12
154
HO
OH
H
COOH
HO H
COOH
deoxycholic acid lithocholic acid
155
(3) Enterohepatic Cycle of bile acids
Conversion to bile salts, that are secreted into the intestine, is the only mechanism by which cholesterol is excreted.
Most bile acids are reabsorbed in the ileum , returned to the liver by the portal vein, and re-secreted into the intestine. This is the enterohepatic cycle.
156
(4) Function of bile acids
Bile acids are amphipathic, with detergent properties.
• Emulsify fat and aid digestion of fats & fat-soluble vitamins in the intestine.
• Increase solubility of cholesterol in bile.
157
2. Conversion of cholesterol into steroid hormones
• Tissues: adrenal cortex, gonads
• Steroid hormones: cortisol (glucocorti-coid), corticosterone and aldosterone (mineralocorticoid), progesterone, testosterone, and estradiol
158Steroids derived from cholesterol
159
3. Conversion into 7-dehydrocholesterol
160
Esterification of cholesterol
• in cells
HO OCR
O
cholesterol cholesteryl ester
acyl CoA cholesterol
acyl transferase(ACAT)
acyl CoASHCoA
161
in plasma
162
Plasma Lipoproteins
163
Plasma lipids
1. Cholesterol 140-220 mg/dl (70% CE
and 30% free cholesterol)
2. Phospholipids 150-200 mg/dl
3. Triacylglycerol 50-155 mg/dl
4. FFA 6-16 mg/dl
164
Structure
165
Types and Separation
166
Classification of plasma lipoproteins
1. electrophoresis method:
- Lipoprotein fast
pre -Lipoprotein
-Lipoprotein
CM (chylomicron) slow
167
2. Ultra centrifugation method:
high density lipoprotein (HDL) high
low density lipoprotein ( LDL)
very low density lipoprotein ( VLDL)
CM (chylomicron ) low
168
Composition
169electron microscope
170
- +
Origin CM
LDL VLDL HDL
Pre-
CM
Separation of plasma lipoproteins by electrophoresis on agarose gel
171
§ 5.3 Structure
172
§ 5.4 Composition of lipoprotein
CM VLDL LDL HDL
Density(g/ml) <1.0060.95-1.006
1.006-1.063
1.063-1.210
Protein 2 10 23 55
Phospholipids 9 18 20 24
Cholesterol 1 7 8 2
Cholesteryl esters 3 12 37 15
TG 85 50 10 4
173
§ 5.5 Apolipoproteins
174
Functions of apolipoproteins
a . To combine and transport lipids.
b . To regulate lipoprotein metabolism.
apo A II activates hepatic lipase ( HL) apo A I activates LCAT
apo C II activates lipoprotein lipase ( LPL)
c. To recognize the lipoprotein receptors.
175
Functions• 1- Lipids are water insoluble compounds. Thus they cannot
be transported in plasma
• 2- Lipids are conjugated to proteins to form lipoproteins which are water soluble and can be transported in plasma.
• 3- These proteins are synthesized by the liver and called: apolipoproteins. They are 5 classes: A, B, C, D and E.
• 4- Failure of liver to synthesize apolipoproteins leads to accumulation of fat in liver and this condition called: fatty liver.
176
1. CM
• Chylomicrons are formed in the intestinal mucosal cells and secreted into the lacteals of lymphatic system.
177
Cholesterol phospholipids
Triacylglycerols andcholesteryl esters
Apolipoproteins structure of CM
178
Metabolism of Chylomicrons
179
summary of CM• Site of formation: intestinal mucosal
cells
• Function: transport exogenous TG• key E: LPL in blood HL in liver
• apoCⅡ is the activator of LPL
• apo E and apo B-48 will be recognized by the LRP receptor
180
2. VLDL
• Very low density lipoproteins (VLDL) are synthesized in the liver and produce a turbidity in plasma.
181
Metabolism of LDL and VLDL
182
Summary of VLDL
• Formation site: liver
• Function: VLDL carries endogenous triglycerides from liver to peripheral tissues for energy needs.
• key E: LPL in blood
HL in liver
183
3. LDL
• Most of the LDL particles are derived from VLDL, but a small part is directly released from liver. They are cholesterol rich lipoprotein molecules containing only apo B-100.
184
3. LDL
• Most of the LDL particles are derived from VLDL, but a small part is directly released from liver. They are cholesterol rich lipoprotein molecules containing only apo B-100.
185
186
Internalization Lysosomal hydrolysisLDL binding
LDL receptors
Cholesterolester
protein
LDL
Cholesterol
Cholesteryloleate
Amino acids
187
Michael Brown and Joseph Goldstein were awarded Nobel prize in 1985 for their work on LDL receptors.
188
Summary of LDL
• Formation site: from VLDL in blood
• Function: transport cholesterol from liver to the peripheral tissues. LDL concentration in blood has positive correlation with incidence of cardiovascular diseases.
189
4. HDL
• LDL variety is called “ bad cholesterol” whereas HDL is known as “ good cholesterol” .
190
VLDL LDL
HDL
Cholesterol
HeartLiver
“BAD”
Deposit
Excretion
“Good”
Forward and reverse cholesterol transport
191
Reverse cholesterol transport
• Cholesterol from tissues reach liver, and is later excreted. This is called reverse cholesterol transport by HDL.
192
Metabolism of HDL
193
194
CETP
• Cholesterol ester transfer protein (CETP) transfer cholesterol ester in HDL to VLDL and LDL.
195
Summary of HDL
• Formation site: liver and intestine
• Function: transport cholesterol from peripheral tissues to liver
196
summary of lipoprotein metabolism
197
Hyperlipidemias
classification Lipoprotein Blood lipids
Ⅰ CM TAG↑ ↑ ↑ CH↑
Ⅱa LDL CH↑ ↑
Ⅱb LDL, VLDL CH↑ ↑ TAG↑ ↑
Ⅲ IDL CH↑ ↑ TAG↑ ↑
Ⅳ VLDL TAG↑ ↑
Ⅴ VLDL, CM TAG↑ ↑ ↑ CH↑
198
Role of Ox LDL in plaque formation and atherosclerosis
199
200
2- Secondary hyperlipoproteinemia:These abnormalities are associated with other diseases as:a) Diabetes mellitus. b)Hypothyroidism.c) Nephrotic syndrome.d) Obesity.e) Obstructive jaundice.
B- Hypolipoproteinemia:1) Abetalipoproteinemia:- Characterized by absence of LDL (β-lipoprotein). It is
associated with low concentrations of chylomicrons and VLDL.
2) Tangier disease:a- Due to deficiency of LCAT enzyme.b- Characterized by low concentration of HDL with
accumulation of cholesterol in tissues.
201
FATTY LIVER
I. Definition:-This is an accumulation of abnormal amount of fat in the liver for a long time with subsequent compression of liver cells.
II- Causes:
A- Over mobilization of fat from extrahepatic tissue to the liver.
B- During high carbohydrate diet.
C- Under mobilization of fat from the liver to the plasma.
202
A. Causes of over mobilization of fat from extrahepatic tissue to the liver:
1- During high fat diet.
2- Due to excessive lipolysis as in carbohydrate low diet, starvation and diabetes mellitus.
B. High carbohydrate diet:
- On high carbohydrate diet, liver is first saturated with glycogen, then any further amount of carbohydrate will be converted to triacylglycerols (lipogenesis).
203
C. Causes of under mobilization of fat from liver to the plasma:
- This is due deficiency any factor essential for plasma lipoproteins formation.
These factors are:1- Decreased synthesis of apoprotein (lipoprotein).2- Failure in formation of phospholipids.3- Failure in conjugation of apoprotein with triacylglycerols
or phospholipids.4- Failure in secretion of lipoprotein from liver to plasma.5- Liver poisons: As carbon tetrachloride, chloroform, lead
and arsenic. They cause fatty liver either by:a- Inhibition of formation of apoprotein.b- Inhibition of conjugation of apoprotein with lipids.c- Inhibition of secretion of lipoprotein.6- Alcoholism: Ethanol stimulates lipogenesis, inhibiting fatty