Lecture 8 Lipid digestion and catabolism
Saturday, 29 September 2012
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
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
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
These contain apolipoproteins B-100 and A-I and TG.