Lecture 8 Lipid digestion and catabolism.docx

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Biological Sciences
Ken Scott

Lecture 8 Lipid digestion and catabolism Saturday, 29 September 2012 5:42 p.m. Dietary fat:  Unsaturated fat: contains double bonds  Saturated fat: contains no double bonds  Consists of Triglycerides, phospholipids and cholesterol esters.  All are poorly soluble in water and therefore difficult to digest and absorb.  Bile salts are secreted from the gall bladder to help emulsify the lipids. Lipid transport across gut epithelium:  Lipids must be packaged to be absorbed by epithelial cells from the intestinal lumen.  The parcel that transport the lipids in the digestive tract are called micelles, this occurs when several bile salts surround a lipid droplet.  Lipoproteins are used to transport lipids in the blood stream Lipid digestion:  Depends on bile salts, they have hydrophobic and hydrophilic sides, amphipathic, are able to interact with nonpolar lipid and aqueous environment. This is a micelle.  Lipases bind the micelle and degrade it into monoacylglycerols and fatty acids, this occurs in the gut lumen.  Fatty acids bind to albumin in the blood. Occurs in the blood lumen.  The fatty acids are further metabolised in epithelial cells with binding proteins and ATP, this forms a triglyceride. This is reacted with a phospholipid to form chylomicrons (this occur in endoplasmic reticulum)  Cholesterol has OH group where fatty acids can be attached.  Unstaturated fat can not be synthesised by humans, therefore these unsaturated fatty acids linoleic, linolenic and arachidonic acids must be present in diet. Necessary component of phospholipid for membranes Lipoproteins and lipid transport:  Chylomicrons assembled in gut epithelial cells  Consist of triglyceride (TG) + Phospholipid (PL) + cholesterol and lipoprotein.  Are secreted into the lymph system and will eventually enter the blood system.  Some triglycerides are hydrolysed by lipoprotein lipase  Chylomicrons remnants go to the liver and are hydrolysed Lipids in the liver: VLDL's and other lipoproteins complexes are assembled and released from the liver into the  blood stream.  These contain apolipoproteins B-100 and A-I and TG.  Some
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