Lipid Metabolism Flashcards
What are the two essential Fatty Acids?
Linoleic (Omega 6) and Linolenic acids (omega 3).
What are the 6 essential lipids?
Linoleic and Linolenic acids, and the 4 fat soluble vitamins K,A,D,E.
What is the “omega carbon?” How does the omega nomenclature work?
Is the last carbon of fatty acids, the last methyl specifically. The omega nomenclature takes the omega carbon and takes the nearest double bond from that carbon, and then subtracts the number of carbons from the nearest double bond. I.e. Lenoleic acid is 18 C’s (9,12), the omega carbon is 18 and the nearest db is 12, 18-12 = 6. Thus Lenoleic acid is Omega 6.
Which isoform, cis or trans, is preferred by the body and why?
We prefer the cis conformation and in fact most fatty acids are in the cis conformation. The trans formation (and saturated) would mess with membrane fluidity, and further they increase the risk of atherosclerosis.
Where and how are triglycerides digested?
It is digested in the small intestines, specifically in the duodenum where bile from the liver will come in and emulsify the fat into micelles, and pancreas will release pancreatic lipase, which also requires colipase to be released from the pancreas for the lipase to work.
In order for the pancreatic lipase to work, what co enzyme must be present and why?
Pancreatic lipase must have colipase to work, and the colipase will active the lipase by increasing the pH to 6 as well as protect the lipase from the bile.
What does pancreatic lipase break down triglycerides to?
Lipase will cleave off the fatty acids from carbon 1 and 3 from the glycerol, leaving the middle fatty acid on carbon two attached to the glycerol - this compound is called 2-monoacyl glycerol (one fatty acid attached to 2nd carbon on glycerol). Net result: 2-monoacyl glycerol + 2 Fatty acids.
Trace the sequence of TG digestion?
From the alimentary canal the TG’s pass through the stomach and into the duodenum, where it will mix with bile, be emulsified and turned into micelles. These micelles will be broken down into 2-MG and 2 fatty acids by Pancreatic Lipase and Colipase, and then be absorbed into the intestinal villi. Once in the villi. it will be reformed into TG’s (because TG’s is not permeable to the intestinal villi thus it needed to be broken down first) and then packaged into chylomicrons. Chylomicrons go into the lymph and then gets dumped into the blood stream via thoracic duct.
What are the key components necessary in order for a cell to make fatty acids, and when do we make fatty acids?
We make fatty acids after eating a large carb-rich meal. We need Acetyl CoA, NADPH, CO2 and ATP.
Where does fatty acid synthesis take place?
In the cytoplasm.
How does the cell acquire the ATP needed to make fatty acids?
Glycolysis in the cytoplasm yields pyruvate, which enters the mitochondria, and through PDH turns into acetyl CoA. Acetyl CoA combines with OAA and turns into citrate and intiates the Krebs cycle and cranks out the ATP.
Where do we get the acetyl CoA needed for fatty acid synthesis?
The DIRECT source of acetyl CoA is from CITRATE in the cytoplasm. In the mitochondria the acetyl CoA + OAA will form citrate which will enter the krebs cycle, but eventually enough ATP and NADH will build up, inhibit isocitrate DH, krebs cycle cannot go forward anymore so it will back up the citrate. It will then be shuttled out of the mitochondria through the CITRATE SHUTTLE, and once in the cytoplasm citrate gets cleaved into Acetyl CoA and OAA.
What are the 2 sources of NADPH for fatty acid synthesis coming from?
Most comes from the Hexose Monophosphate (HMP) Shunt that uses G6PD as its main enzyme. Second source is the OAA that was cleaved from the citrate in the cytoplasm (this OAA came from the citrate shuttle from mitochondria). OAA will get turned into Malate, and malate will use the enzyme MALIC ENZYME to turn into pyruvate. In the process of turning into pyruvate malic enzyme uses NADP+ as a cofactor and turns it into NADPH, hence the second source.
