Fatty acids are an important source of energyOxidation is the process where energy is produced by degradation of fatty acids

There are several types of fatty acids oxidation. - oxidation of fatty acid - oxidation of fatty acids - oxidation of fatty acids

Beta-oxidation is the process by which fatty acids, in the form of Acyl-CoA molecules, are broken down in mitochondria and/or in peroxisomes to generate Acetyl-CoA, the entry molecule for the Citric Acid cycle.It occurs in many tissues including liver kidney and heart.Fatty acids oxidation doesn't occur in the brain, as fatty acid can't be taken up by that organ.

The beta oxidation of fatty acids involve three stages:

Activation of fatty acids in the cytosolTransport of activated fatty acids into mitochondria (carnitine shuttle)Beta oxidation proper in the mitochondrial matrix

1) Activation of FA:

This proceeds by FA thiokinase (acyl COA synthetase) present in cytosol Thiokinase requires ATP, COA SH, Mg++. The product of this reaction is FA acyl COA and water.

Long chain acyl CoA traverses the inner mitochondria membrane with a special transport mechanism called Carnitine shuttle.The matrixThe cytosol

Acyl groups from acyl COA is transferred to carnitine to form acyl carnitine catalyzed by carnitine acyltransferase I, in the outer mitochondrial membrane.Acylcarnitine is then shuttled across the inner mitochondrial membrane by a translocase enzyme.

The acyl group is transferred back to CoA in matrix by carnitine acyl transferase II.

Finally, carnitine is returned to the cytosolic side by translocase, in exchange for an incoming acyl carnitine.

There are 4 steps in C oxidation Step I Oxidation by FAD linked dehydrogenaseStep II Hydration by HydrataseStep III Oxidation by NAD linked dehydrogenaseStep IV Thiolytic clevage Thiolase

The first reaction is the oxidation of acyl CoA by an acyl CoA dehyrogenase to give - unsaturarted acyl CoA (enoyl CoA). FAD is the hydrogen acceptor.

The second reaction is the hydration of the double bond to -hydroxyacyl CoA (p-hydroxyacyl CoA).

The third reaction is the oxidation of -hydroxyacyl CoA to produce -Ketoacyl CoA a NAD-dependent reaction.

The fourth reaction is cleavage of the two carbon fragment by splitting the bond between and carbonsBy thiolase enzyme.

The release of acetyl CoA leaves an acyl CoA molecule shortened by 2 carbons.

This acyl CoA molecule is the substrate for the next round of oxidation starting with acyl CoA dehydrogenase.

Repetition continues until all the carbons of the original fatty acyl CoA are converted to acetyl CoA.

In the last round a four carbon acyl CoA (butyryl CoA) is cleaved to 2 acetyl CoA.

Energetics of FA oxidation e.g. Palmitic (16C):

-oxidation of palmitic acid will be repeated 7 cycles producing 8 molecules of acetyl COA.

In each cycle FADH2 and NADH+H+ is produced and will be transported to the respiratory chain.FADH2 2 ATPNADH + H+ 3 ATPSo 7 cycles 5x7 = 35 ATP

Each acetyl COA which is oxidized in citric cycle gives 12 ATP (8 x 12 = 96 ATP)

2 ATP are utilized in the activation of fatty acid (It occurs once).Energy gain = Energy produced - Energy utilized= 35 ATP + 96 ATP - 2 ATP = 129 ATP

Non-covalent assemblies of lipids and proteinsLP coreTriglyceridesCholesterol estersLP surfacePhospholipidsProteinscholesterolFunction as transport vehicles for triacylglycerols and cholesterol in the bloodAll the lipids contained in plasma, including fat, phosphalipids, cholesterol, cholesterol ester and fatty acid, exist and transport in the form of lipoprotein

CMVLDLLDLHDLLipoprotein Nomenclature, Composition and separationMajor apoB 48 apoB 100 apoB 100 apoA-IProtein

Major TG TG CE CELipid

1.Electrophoresis method: CM (chylomicron) slow -Lipoprotein pre -Lipoprotein fast- Lipoprotein2. Ultra centrifugation methodCM (chylomicron ) slowvery low density lipoprotein ( VLDL) low density lipoprotein ( LDL) high density lipoprotein (HDL) high

They are protein components of lipoproteins consisting 60% of some lipoproteins (HDL) and 1% of some lipoproteins (chylomicrons)To combine and transport lipids.To recognize the lipoprotein receptorsApo-B100 is the ligand for LDL-receptors Apo-B48 for chylomicron remmenantApo-A1 is the ligand for HDL receptor.Activators for certain enzymes involved in lipoprotein metabolism Apo C II activates lipoprotein lipase and apo-A1 activates LCAT (Lecithin Cholesterol Acyltransferase, formation of cholesterol esters in lipoproteins).

All lipids in plasma are transported in the form of lipoproteins .

Transport dietary lipids from intestine to liver (exogenous) Chylomicrons

Transport lipids from liver to peripheral tissues (endogenous) VLDL (very low density lipoproteins)

Synthesized in small intestineTransport dietary lipids (exogenous TG)98% lipid, large sized, lowest densityApo B-48Receptor bindingApo C-IILipoprotein lipase activatorApo ERemnant receptor bindingChylomicronsNascent chylomicron are formed in the intestinal and consists of rich in dietary TG + minimal amount of dietary cholesterol + Apo (B-48)Mature chylomicron after Nascent chylomicron passage to blood, addition of apoC and apoE from HDLLipoprotein lipase hydrolyzes TG present in chylomicrons Chylomicron remnant taken up by the liver through endocytosis.Apo C removed and returns to HDL

Synthesized in liverTransport endogenous triglycerides90% lipid, 10% proteinApo B-100Receptor bindingApo C-IILPL activatorApo ERemnant receptor bindingThe major fraction of VLDL remnant further loses TG, so as to be converted to LDLVery Low Density Lipoprotein (VLDL)Nascent VLDLare formed in the liver and consists of endogenous TG + 17 % cholesterol + Apo (B-100)Mature VLDL after Nascent VLDL passage to blood, addition of apoC, apoE and cholesterol esters from HDLLipoprotein lipase (LPL) hydrolyzes TG present in VLDL VLDL remnant containing less of TG and more of cholesterol and taken up by the liver through endocytosis.Apo C removed and returns to HDL

Cholesterol is the most important animal sterols which is the precursor of all other steroid in the body e.g. corticosteroids, sex hormones, bile acids and vitamin D.Cholesterol biosynthesis:All tissues containing nucleated cells are capable of synthesizing cholesterol.

Cholesterol is derived about equally from the diet (exogenous) or manufactured de novo (endogenous) in cells of humans especially in liver , intestine, and adrenal cortex .

Acetyl CoA is the source of all carbon atoms in cholesterol.

The liver is the main source of plasma cholesterol but intestine also participates.

The liver is the principle organ which removes cholesterol from blood.

The enzymes involved in cholesterol biosynthesis are present in cytosol and microcosms of the cell.Total cholesterol in plasma is normally between 140-300 mg/dl.Cholesterol esters are continually hydrolysed in liver and resynthesized in plasma.Cholesterol is present in all the lipoproteins but in fasting more than 60% is carried in (LDL).

Formation site: from VLDL in blood, but a small part is directly released from liverFunction: transport cholesterol from liver to the peripheral tissues.Carries aprox. 50% of blood cholesterol. containing only apo B-100. LDL concentration in blood has positive correlation with incidence of cardiovascular diseases. Expulsion cholesterol from the cell, and transported by HDL and finally excreted through liver.

Formation site: liver and intestineFunction: transport cholesterol from peripheral tissues to liver (reverse cholesterol transport) converted cholesterol to bile acids and excretedReservoir of apoproteins Contain protein, CholesterolApo AApo C Activates LPLApo E Remnant receptor bindingProtects against heart disease