Glycerophospholipids and Lipoproteins - PowerPoint Presentation

Slide1

Glycerophospholipids and Lipoproteins

Glycrophospholipids degradation

Lipoproteins

Slide2

G

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

Slide3

This 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

Slide4

This 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

Slide5

This Phosphatidyl choline model shows the two hydrophobic tails and the polar head made from phosho- choline.

Slide6

This 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

Slide7

G

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

Slide8

This 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

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Transport of TAG by Plasma Lipoproteins

Slide12

This 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)

Slide13

TRI

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)

Slide14

PHOSPHO

ACYL

GLYCEROL

G

LY

CEROL

FATTY ACID

FATTY ACID

Phosphate

-

Alcohol

+

Slide15

Triacylglycerol that is

NOT

soluble in water

(but can be mixed with water in the presence of phospholipid like phosphatidylcholine)

Slide16

Lipoproteins

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

Slide17

Apolipoproteins

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

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This is a schematic representation of lipoprotein particle.

Notice the large number of molecules represented by the small circles

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This 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

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Classes 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

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Composition 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

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The 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.

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Lipoproteins 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.

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Lipoprotein

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

Slide25

Next Topic is digestion of lipids