BIOC2600 1.6

• Lipid Metabolism is taught by Dr. Masayo Kotaka, a professor in the School of Biomedical Sciences at the LKS Faculty of Medicine.
• The learning objectives of the Lipid Metabolism course include understanding the processes in digestion of fats, comparing and contrasting the breakdown and synthesis of fatty acids, explaining the production of ketone bodies, outlining the synthesis of triacylglycerol and phospholipids, and classifying different lipoproteins and their functions.
• Cells can obtain fatty acid fuels from three sources: fats consumed in diet, fat stored in cells as lipid droplets, and fats synthesised in one organ and transported to another.
• Vertebrates obtain fats from diet, mobilising fat stored in specialised tissues and in the liver, and converting excess dietary carbs to fats for export to other tissues.
• Fats are an important source of dietary calories, typically contributing 30 - 40% of calories in the American diet.
• Transport into mitochondria does not need the carnitine shuttle for fatty acids with 12 or less carbons.
• During the oxidation process, the β - CARBON is attacked.
• The carnitine - mediated entry process is the rate - limiting step for the oxidation of fatty acids in mitochondria.
• Beta( β ) - oxidation in the mitochondrial matrix is required for fatty acids with 12 or less carbons, involving only steps 1 and 3.
• Activation of fatty acids in the cytosol produces fatty acyl CoA, catalysed by a family of acyl - CoA synthetase isozymes for fatty acids with short, intermediate or long carbon chains in the outer mitochondrial membrane.
• Fatty acids destined for mitochondrial oxidation will have to be attached to carnitine to form fatty acyl - carnitine, which will then be transported into the matrix of the mitochondria from the cytosol via the carnitine shuttle.
• Fatty acid oxidation occurs in the mitochondria, with even-numbered fatty acids broken down by β - oxidation and acetyl CoA is released.
• Conversion to fatty acyl - carnitine from fatty acyl CoA commits the fatty acyl group to the oxidative fate.
• FAs are bound to fatty acid synthase in the synthesis of fatty acids.
• FAs are bound to CoA in the synthesis of fatty acids.
• In cytosol, fatty acid synthesis involves the addition of 2C units via malonyl CoA, with Acetyl CoA as the precursor.
• Palmmitate serves as the precursor of other long-chain fatty acids.
• A different enzyme is required for each reaction in the synthesis of fatty acids.
• The reactions in fatty acid synthesis occur in one multifunctional enzyme complex.
• The oxidative process of fatty acid synthesis requires NAD and FAD.
• When [acetyl - CoA] and [ATP] in mitochondria increase, citrate is transported out and becomes the precursor of cytosolic acetyl - CoA and activator of malonyl - CoA production.
• The reductive process of fatty acid synthesis requires NADPH.
• Glucagon and epinephrine triggers phosphorylation of the enzyme and stops malonyl CoA production.
• In the mitochondrial matrix, fatty acid synthesis involves the removal of 2C units, resulting in Acetyl CoA as the product.
• Citrate is also another point of control in the regulation of fatty acid synthesis.
• When a cell or organism has more than enough metabolic fuel to meet its energy needs, the excess is converted to fatty acids and stored as lipids.
• The reaction of converting acetyl - CoA to malonyl - CoA is the rate limiting step and site of regulation, with palmitoyl - CoA as a feedback inhibitor of the enzyme.
• The enzymes of fatty acid oxidation are located inside the mitochondrial matrix.
• Apolipoproteins are lipid-binding proteins responsible for the transport of triacylglycerols, phospholipids, cholesterols, cholesteryl esters between organs.
• Fatty acids with 12 or less carbons can enter the mitochondria without the help of membrane transporters.
• In the capillaries of these tissues, the triacylglycerol in the chylomicron is hydrolysed into fatty acids and glycerol by lipoprotein lipase and taken up by the tissues.
• Those with 14 or more carbons (the majority of fatty acids) cannot pass directly and needs help.
• Digested fatty acids and monoacylglycerols are absorbed by the villi in the small intestines, re-assembled into triglycerides, packed into particles called chylomicrons and enter the lymphatic system.
• For fatty acids with 14 carbons or more, there are three stages of fatty acid degradation: activation of fatty acids in the cytosol, transport of fatty acids into the mitochondria, and beta-oxidation.
• In fat tissues, fatty acids and glycerol are re-esterified to triacylglycerol for storage.
• The remnants of chylomicron depleted of triacylglycerol will be travel to the liver and be taken up by endocytosis.
• Chylomicrons are lipoprotein particles made up of lipids and apolipoproteins.
• Emulsification is the process where bile acids are added to fat droplets in the duodenum, creating a detergent-like property that emulsifies fats into mixed micelles containing bile salts and triacylglycerols.
• Apolipoproteins combine with lipids to form different classes of lipoprotein particles, with chylomicron being just one class.
• Chylomicrons enter the blood via the lymphatic system and are carried to fat tissues and muscles.