Ch. 6 Combination Molecules (Lipoproteins, Glycolipids, Glycoproteins, Etc.)

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Lipoproteins

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1. trams for bodily transport of triglycerides and cholesterol (non-soluble)
2. Have polar/non-polar groups which allows for solubilization of lipids + solubility in blood.

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The walls of lipoproteins trams are composed of:

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1. cholesterol, phospholipids and apoproteins

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What determines the specific function of the lipoprotein?

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The type of apoprotein in the wall of the lipoprotein tram.

There are many types of apoproteins.

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Major lipoprotein types include:

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1. chylomicrons
2. VLDL (very low density lipoproteins)
3. LDL (low density lipoproteins)
4. HDL (high density lipoproteins)

*Based on lipoprotein weights upon ultracentrifugation/electrophoresis.

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Cholesterol ester

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A cholesterol ester is a cholesterol in which a fatty acid is attached to cholesterol's -OH group.

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Explain what happens to fats and cholesterols ingested in meals?

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Since hamburgers contain triglycerides and cholesterol esters (neither of which are soluble in water), they are a fatty lump. They must be digested, absorbed and distributed in the body.

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Fat/cholesterol ester digestion

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1. stomach breaks fats into smaller particles
2. Bile salts (with polar/nonpolar regions) emulsify them into droplets (micelles) that are suluble with a broad surface/interaction area for digestive enzyme interaction.
3. pancreatic lipase- breakdown of triglycerides -->fatty acids + monoglycerides

4. Pancreatic/intestinal wall esterases breakdown cholesterol esters to free cholesterol and fatty acids.

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2. Triglyceride/ cholesterol ester absorption

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1. Free fatty acids, monoglycerides, and free cholesterol enter the small intestinal cell

2. Monoglycerides and free cholesterol are re-esterified (with free fatty acids). This results in the reformation of triglycerides and cholesterol esters (as well as free cholesteroL) and incorporation into "chylomicrons" which carry triglycerides and cholesterol-->lymph-->general systemic circulation.

3. Some free fatty acids (small/medium chain) can enter the venous circulatoin directly, are not too soluble, and attach to albumin.

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3. Triglyceride/ cholesterol ester distribution in the body

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1. chylomicrons drop off triglycerides to fat cells. They drop fatty acids from triglycerides off to skeletal/heart muscle cells for energy sources.

Following release of fatty acid from triglyceride via lipoprotein lipase on capillary endothelium of muscle and fat, free fatty acids enter muscle/fat where they may be reesterified to triglycerides.

Remaining "remnent" particles (rich in cholesterol), zoom to liver, which knows what to do with cholesterol!

Excess cholesterol arriving to liver can be excreted as bile salts OR exported along w/ triglycerides as VLDL particles.

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Lipoprotein lipase

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Located on capillary endothelial cells of muscle and fat tissues, they serve to:

1. release fatty acid from triglyceride

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VLDL, LDL, and IDL

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particles are released by liver, rich in triglycerides/cholesterol, and drop off their triglycerides in fat/muscle.

The remainder of particles become cholesterol rich LDL (after going through an intermediate IDL stage)

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LDL cholesterol distribution.

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VLDL excreted from the liver, after dropping off their contents in fat and muscle cells, become LDL.

LDL distributes the cholesterol widely to hepatic and non-hepatic cells, which is important since cholesterol is a major component of cell membranes.

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HDL

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HDL is a scavenger that carries unwanted, excess cholesterol, partly from cell breakdown, back to the liver (largely as LDL remnants) where cholesterol might end up being excreted (for instance, as bile salts).

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LCAT

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LCAT (lecithin-cholesterol acyl transferase) is an enzyme associated with HDL that reesterifies free cholesterol

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Glycolipids

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1. Combinations of sugars and lipids.

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ceramide

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backbone of the glycolipid molecule.

Serine is a 3-carbon coat rack. When a fatty acid is hung on its -COOH group, it becomes sphingosine. When a further fatty acid attaches to -NH2 group it becomes a ceramide. This leaves the third carbon of ceramide w/ -OH group free for reaction with other molecules.

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Sphingomyelin

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Phosphocholine attaches to the free -OH group of ceramide (which is a serine w/ 2 fatty acids on -COOH and -NH2)

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Glycolipids

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If sugars attach to ceramide's free OH (ceramide is a serine w/ 2 fatty acids on -COOH and -NH2) then we get glycolipids cerebroside and ganglioside.

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Cerebrosides vs. ganglioside

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Cerebrosides simpler than gangliosides. Cerebrosides generally have either glucose or galactose attached to ceramide's free -OH group.

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Sulfatides

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Cereocides that contain a sulfate group attached to the galactose part of the molecule. Sulfatides are found in significant amounts in the brian.

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Ganglioside

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longer, branched-chain sugars attach to third carbon -OH group of ceramide.

A way to remember this is the sugars "gang up" in a ganglioside.

Also they contain at least one molecule of a sialic acid (an 11-carbon amino sugar called N-acetyl neuraminic acid, NANA).


Sugars are branched in a complex way and attach to ceramide via glucose.

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Globosides

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Glycolipids that are intermediate in complexity between cerebrosides and gangliosides. (two or more sugar resides, but no sialic acid).

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Amino sugar formation:

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1. Fructose 6-P + -NH2 group from glutamine --> (6C) glucosamine 6-P (an amino sugar)

2. Subsequent transformations--> other amino sugars (ie. n-acetyl galactosamine (8C) component of globoside/ganglioside, portion of antigen that determines blood group type A whereas galactose determines B)

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Sialic acids

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11 carbon amino sugars (important component of gangliosides)

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Examples of glycoproteins in the body:

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antigens associated with A, B, and O blood groups; antigenic sites on cells; cell membrane components; immunoglobulins, complement; and blood clotting proteins; certain hormones; interferon; collagen; secretions (mucins) which may lubricate.

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Proteoglycan (definition and structure)

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A molecule in which carbohydrates overwhelmingly predominate.

Structure: Contains a central protein core, to which are attached numerous mucopolysaccharide chains (commonly including hexosamine sugars and uronic acid)

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Carbohydrate portion of proteoglycan

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Mucopolysaccharide (or glycosaminoglycans).

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Some of the common mucopolysaccharides include:

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1. Hyaluronic acid.
2. Chondroitin sulfate
3. Dermatan sulfate
4. Heparin
5. Heparan sulfate
6. Karatan sulfate

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Properties of mucopolysaccharides

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1. absorb lots of water, and tend to have a mucoid, or viscous consistency (leading to their structural/lubricatory role in connective tissue).

2. Maintain fluid and electrolyte balance throughout body.

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Hyaluronic acid differs from other five types of mucopolysaccharides in that:

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it has not been shown to attach to the core protein, but provides a backbone for proteoglycan aggregates. It is also not sulfated.