5A-Digestion and Transport of Lipids Flashcards
What is the general strucutre of the triacylglycerol?
Triacylglycerol contains a glycerol backbone to which three fatty acids are esterfied.
The length of the fatty acids can vary from short or medium chains which contain 12 or fewer carbons
Long chains contain greater than 12 carbons. The length of fatty acid chain dictates the route of digestion of the triacylglycerol.
What is the general synthesis of a triacyclglycerol?
What is the general strucutre of VLDL?
The excess carbohydrates are converted to triacylgylcerols in the smooth endoplasmic reticulum to become part of the VLDL. The TGs are packed with cholesterol, phospholipids and proteins which are synthesized in the rough endoplasmic reticulum. The major structural protein of VLDL is Apoprotein B-100. One long apoB-100 protein is wound through the surface of the VLDL.
Where are short and medium chain lipases located? Why there?
Short or Medium chains are digested by lingual lipase located at the back of the tongue and by gastric lipase found in the stomach.
Lingual lipase and gastric lipase are most active in infants and young children who drink large quantities of cows milk because it contains large amounts of short and medium chain fatty acids
How is long chain fatty acids taken up into the intestinal cell?
in the small intestine, bile salts emulsify the fat –> colipases remove the bile salt restriction on pancreatic lipase –> lipase hydrolyzes the fatty acids to free FA’s and 2-monoacylglycerol –> FA’s and glycerol packaged into micelles with other things (cholesterol, lysophospholipids and fat soluble vitamins)–> micelles travel through microvilli into the intestinal epithelial cells
What does the pancreatic lipase do?
The enzymatic action of pancreatic lipase is to cleave position 1 and 3 of the TG resulting in fatty acids and 2-monoacylglycerol being produced.
What are the 3 things pancreatic lipase depends on to work properly?
How are chylomicrons made and what do they do?
the free fatty acids and the monoacylglycerol are resynthesized to TG in the smooth ER
A chylomicrons contains TGs along with proteins (apo-48 from RER), phospholipids, cholesterol, and fat soluble vitamins TGs are the main component of chylomicrons
assembly of chylomicrons takes place in golgi and RER
exocyotosed into lymphatic system
Where are bile salts recycled back into the enterohepatic circulation?
ileum
What % of bile salts is reabsorbed?
95% of bile salts are reabsorbed while 5% or less is loss in stool
What are the hydrophobic and hydrophilic parts of the chylomicron and why does this matter?
One the inside of the chylomicron are the cholesterol and TG which are located there because of their hydrophobic nature
The phospholipids are oriented with their hydrophobic tails facing inward and hydrophilic heads outward like in a cell membrane
The proteins that are required for the chylomicrons are on the surface which allows for it to carry out its needed duties
What are the components of the chylomicron?
Composed of TGs cholesterol, cholesterol ester, phospholipid, and proteins
The proteins that are found in a chylomicron are apoB-48 apoE, and apoCII
What adds the ApoE and ApoCII to form the mature chylomicron?
HDL
How is Apo-100 and Apo-48 made?
A single gene is used to encode for both apoB-48 and apoB-100. In the intestine the primary transcript of the gene undergoes RNA editing. A stop codon is generated that causes the protein to be produced in the intestine that is 48% shorter then apoB-100 produced in the liver. This is the reason for numerical naming of the apo proteins.
What is the role of Apo E?
this is a protein transferred to a nascent chylomicron via HDL. Apo E is recognized by surface receptors of the liver- this allows ApoE bound proteins to nter the liver cells
