Glycrophospholipids degradation Lipoproteins G L Y C E R O L FATTY ACID FATTY ACID PHOSPHOACYLGLYCEROL PHOSPHATE ALCOHOL Again this is the representation structure of glycerophospholipids ID: 935295
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Slide1
Glycerophospholipids and Lipoproteins
Glycrophospholipids degradation
Lipoproteins
Slide2G
L
Y
CEROL
FATTY ACID
FATTY ACID
PHOSPHOACYLGLYCEROL
PHOSPHATE
ALCOHOL
Again this is the representation structure of glycerophospholipids.
we will review in this lecture their emulsifying function, then their degradation will be shown and lipoproteins structure
Slide3This is the common phospholipid Phosphatidyl choline. Notice that the polar head carries one negative one positive charges and it contains two hydrophobic hydrocarbon chains. It is amphipathic molecule able to form micelles
Slide4This is the common phospholipid Phosphatidyl choline. Notice that the polar head carries one negative one positive charges and it contains two hydrophobic hydrocarbon chains. It is amphipathic molecule able to form micelles
Slide5This Phosphatidyl choline model shows the two hydrophobic tails and the polar head made from phosho- choline.
Slide6This is the is the structure of micelles when phospholipids like Lecithin is mixed well with water
Large number of molecules aggregate to make this structure where the interior is hydrophobic and the surface is hydrophilic able to interact with water
If Lecithin is well mixed well with water and oil (or fat), the oil molecules will get into the interior of the micelles therefore the oil is mixed.
The mixture (known as emulsion) has milky appearance because the very small micelles which contain oil are suspended in water
oil
oil
oil
oil
Slide7G
L
Y
CEROL
FATTY ACID
FATTY ACID
Degradation of Phospholipids:
Phospholipase A1Phospholipase A
2Phospholipase CPhospholipase D
PHOSPHATE
ALCOHOL
Glycerophospholipids have 4 ester bonds.
Hydrolysis of each bond is catalyzed by different enzymes. The are known as phospholipases.
Now see the action of each on phospholipid molecule
Q: What are the products produced in the reaction catalyzed by phospholipase C.
A: Diacylglycerol and phosphoalchol.
Q: What are the products produced in the reaction catalyzed by phospholipase D.
A: Phosphatidic acid and alcohol
Slide8This molecule is known as lysophosphatidyl choline. It is produced by the action of a phospholipase
Q: which phospholipase ?
A: phospholipase
A
2
Notice that phospholipases don’t act sequentially
(The product of one phospholipase is Not the substrate for the next).So which phospholipase catalyzes the hydrolysis of the first fatty acid?
It is not phospholipase
A1
It is lysophospholipase
Slide9Slide10Slide11Transport of TAG by Plasma Lipoproteins
Slide12This is glycerol
Hydrophilic and water soluble( completely soluble in water)
This is an ester bond is much less hydrophilic than the hydroxyl group or carboxyl group . So triacylglycerol is
NOT
soluble in water
This a fatty acid (stearic) has long hydrocarbon chain and small ionizable hydrophilic end. its amphpathic (can form micelles)
Slide13TRI
ACYL
GLYCEROL
G
LY
CEROL
FATTY ACID
FATTY ACID
FATTY ACID
So triacylglycerol is
NOT
soluble in water
(doesn’t have free hydroxyl and carboxyl groups)
Slide14PHOSPHO
ACYL
GLYCEROL
G
LY
CEROL
FATTY ACID
FATTY ACID
Phosphate
-
Alcohol
+
Slide15Triacylglycerol that is
NOT
soluble in water
(but can be mixed with water in the presence of phospholipid like phosphatidylcholine)
Slide16Lipoproteins
Multimolecular Complexes of Lipids and Proteins
For Transport of Lipids in the PlasmaLipids Include TAG TriacylglycerolCE Cholesterol EsterCH CholesterolPL Phospholipids
The name lipoproteins suggests that these are proteins with covalently bound lipid component as in the case of glycoproteins. But this not true because these are complexes of large number of proteins and lipid molecules joined together by non covalent interactions so they are
Lipids as we know are insoluble in water, so how they can be transported in plasma which is 90% water. So the function of lipoproteins
Slide17Apolipoproteins
The Protein Part of Lipoproteins
AmphipathicInclude Several Classes Apo A, Apo B-48, Apo E.…RolesStructuralRegulatoryBinding of lipoproteins to Cell Surface Receptors
Some proteins are formed from protein part and non-protein part. The prefix Apo in the name of any protein refer to the protein part of that protein. Like apoenzyme is the protein part of the enzyme without the nonprotein (coenzyme)
Apolipoproteins are amphipathic so they can interact with hydrophobic part of the lipids and water at the surfaceC
Apolipoproteins have different roles structural for maintaining the structure of the lipoprotein
Regulatory for regulating the metabolism of the lipoproteins
Slide18This is a schematic representation of lipoprotein particle.
Notice the large number of molecules represented by the small circles
Slide19This is another schematic representation of lipoprotein particle We can distinguish two regions in the particle. Surface and core
The interior of the particle is hydrophobic and contains TAG and cholesteryl ester
The surface contains the amphipathic components including
Phospholipids Unesterfied (free) cholesterol (having free hydroxyl group so it is amphpathic)Apoprotein
Slide20Classes of Lipoproteins
Lipoprotein
Density Protein Major LipidChylomicrons <0.95 2 % TAG (85%)VLDL 0.95- 1.006 9% TAG (55%) IDL 1.006-1.019
11% TAG (26%) CE (30%)LDL 1.019- 1.063 20% CE (35%)HDL 1.063- 1.21 45% PL (25%)
D
ENSITY
PROTEI
N %
Majo Lipid
LIPIDS
Several classes of lipoproteins have been identified which can be separated by a technique called ultracentrifigation, very high speed centriguge that produces very high g force.The lipoproteins particles will be separated based in the difference in their density
VLDL : very low density lipoproteinsIntermediate density lipoproteins
LDL Low density
High density lipoproteins
Notice that chylomicrons have the lowest density (Less than that of water)
You are not expected to memorize the exact density.
Notice that there is a range of density for each class. This reflects that they heterogeneous population
Difference in the percentage of the protein makes the density different. The higher the percentage of protein the higher the density
Slide21Composition of Plasma Lipoprotein
The percentage of various lipids and protein components of the 4 major classes of lipoproteins.
More than 70% of HDL components are surface components (Phphospholipids, cholesterol and proteins ) So the surface to volume ratio is high
Slide22The highest surface to volume ratio of HDL means that the size is the smallest.
Imagine that you have a cube with 2*2*2 cm.
If you divide it to 8 cubes
What happens to the surface area
Now look at the relative size of the mahor classes of lipoproteins.
Slide23Lipoproteins can be separated easily by electrophoresis.
They can be separated by the same technique of plasma proteins electrophoresis.
But using a dye that can react with lipids only lipoprotieins can be visualized
Recall that separation of plasma proteins produces the following fractions,
α1,α2, β and γ. So plasma lipoproteins are also identified by the corresponding plasma protein with which they comigrate.Hence HDL for example is also known as α-lipoprotein, while LDLis also known as β lipoprotein
Notice that separation here is not on basis of density but based on charge to mass ratio.The charge is carried by the protein part. Hence chylomicrons which are the largest and contain only 2% protein do not migrate. In electrical field.
Slide24Lipoprotein
Apo Protein Types
Function
ChylomicronsApo B, Apo C, Apo ETransport of dietary lipids from small intestine to tissues
VLDLApo B, Apo C, Apo E
Transport of endogenous TAG produced in the liver to tissues IDLApo B, Apo E
LDLApo
B
Transfer of Cholesterol to tissue
HDL
Apo A, Apo C, Apo E
Cholesterol Return to Liver
Notice that Apo A is found only HDL.
Notice that Apo B is .found in all but HDL
And it is the only one in LDL
Slide25Next Topic is digestion of lipids