L30 Lipids and Lipoproteins 2011

L30 Lipids and Lipoproteins 2011 - COPYRIGHT Mammalian...

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-1/13- COPYRIGHT Prof. Beyenbach Mammalian Physiology BIOAP 4580 2011 Intestinal Absorption: Lipids Lipid Transport in the Plasma by Lipoproteins 1) Lipids are present in the diet as solid fats and liquid oils. Lipids include fatty acids, triglycerides, phospholipids, cerebrosides, and sterols, the structures of which are reviewed below. a) Typical fatty acids b) Triglycerides (triacyl glycerols) These are esters of glycerol and three (3) fatty acids c) Phospholipids I. There are esters of glycerol, two (2) fatty acids and phosphate, such as phosphatidic acid, also known as diacylglycerol (DAG) or glycerol, two fatty acids and phosphate plus inositol, such as phosphatydilinositol (PI).
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-2/13- Recall that diacylglycerol (DAG) and the phosphatidyl inositols (IP 3 , PIP 2 ) are part of an intracellular second messenger system. DAG activates protein kinase C, and IP 3 is a potent releaser of Ca 2+ from intracellular stores. The family of phospholipases (PLC) cleaves sugar inositol from the rest of the molecule, yielding DAG and IP 3 . or glycerol, two fatty acids, phosphate plus choline, such as phosphatidyl choline (lecithin) or glycerol, two fatty acids, phosphate plus ethanolamine, such as phosphatidyl ethanolamine (cephalin) or glycerol, two fatty acids, phosphate plus serine, such as phosphatidyl serine
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-3/13- II. Phosphate-containing derivatives of glycerol such as cardiolipin (diphosphatidyl glycerol) Glycerol-based phospholipids consist of 1) a glycerol ‘backbone’, 2) two esterified fatty acids, and 3) a phosphate group at the third glycerolic hydroxyl group (see DAG, PI, phosphatidyl choline, phosphatidyl ethanolamine, phosphatidyl serine, and cardiolipin above). Fatty acids are nonpolar molecules that dissolve poorly in water. Phosphoglycerol (DAG) is polar and water soluble. Accordingly, associations of DAG and fatty acids are both hydrophilic and hydrophobic, an amphipathic property. When mixed with water, low concentrations of phospholipids assemble spontaneously as a monolayer at the water-air interface. At higher concentrations, phospholipids assemble themselves as micelles, and at still higher concentrations as bilayers, the principal structural component of cell membranes. III. Sphingomyelins. These are esters of fatty acid, phosphate, and choline. Here, the amino acid serine rather than glycerol forms the ‘backbone’ of the molecule. d) Cerebrosides These are compounds consisting of galactose, fatty acid and sphingosine. Note, no phosphate linkages are involved. Again, serine forms the backbone of the molecule.
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-4/13- e) Sterols and steroid hormones. Cholesterol and its derivatives: steroid hormones, bile acids, some vitamins. Among the steroid hormones are glucocorticoids (cortisol and corticosterone), the mineralocorticoid aldosterone, the androgens and estrogens (male and female sex hormones respectively). Cholesterol is a precursor for all these hormones synthesized in the adrenal cortex.
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This note was uploaded on 04/09/2011 for the course BIOAP 4580 taught by Professor Beyenbach,k. during the Spring '11 term at Cornell.

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L30 Lipids and Lipoproteins 2011 - COPYRIGHT Mammalian...

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