Synthesis of Membrane Lipids and Fat Flashcards | Quizlet
23/12/2017 · Synthesis of Lipids: Biochemistry ..
Lipid digestion and absorption
Lipids play an important role in cell structure and metabolism. TAGs are the major storage form of energy. Cholesterol is a component of cell membranes and precursor of steroid hormones. Lipid digestion occurs at lipid water interfaces since TAG is insoluble in water and digestive enzymes are water soluble. Lipids are digested and absorbed with the help of bile salts. Products of lipid digestion aggregate to form mixed micelles and are absorbed into the small intestine. Lipids are transported in the form of lipoproteins.
Synthesis of Lipids - Web Books
Fatty acid oxidation
Fatty acids have to be activated prior to their entry into mitochondrial matrix where the enzymes of β-oxidation of fatty acids are located. Activated fatty acids are then transported from cytosol to the mitochondrial matrix with the help of carnitine transporter. Total net yield of ATP per molecule of palmitic acid is 129. Similarly oxidation of unsaturated and odd chain fatty acids also take place with additional reactions. Β-oxidation in peroxisomes involves three enzymatic reactions. Minor pathways of oxidation such as α-oxidation of branched chain fatty acids and ω-oxidation of medium and long chain fatty acids in microsomes do take place in our body.
Ketone body metabolism
Ketone bodies are acetoacetate, β-hydroxy butyrate and acetone. Ketone bodies are synthesized in the liver but they are utilized by extra hepatic tissues as fuels. Ketone bodies are accumulated in the blood if the rate of synthesis exceeds the ability of extra hepatic tissues to utilize them. This leads to excess ketone bodies in blood, excretion of ketone bodies in urine and smell of acetone in breath. All these three together are known as ketosis. In uncontrolled diabetes mellitus and starvation, ketone bodies are formed.
Two examples are shown in Figures 5-E-1 and 5-E-2
Once formed, acetoacetyl-ACP enters the elongation cycle for fatty acid synthesis. This cycle is the reverse of the of fatty acids discussed earlier. The first step in the elongation cycle is condensation of malonyl-CoA with a growing acetoacetyl-ACP chain. This adds two carbons to the chain. The next three reactions use 2 to reduce the -ketone (red in figure) and generate an acyl-ACP molecule two carbons longer than the original substrate. The acyl-ACP molecule continues through the cycle until the appropriate chain length is reached. In fatty acid chains in lipids are 12-20 carbons long. The length of the fatty acid chains and the number of double bonds (unsaturation) is dependent upon the temperature the bacteria is growing at. The membrane must remain fluid. Using short chain fatty acids with higher degrees of unsaturation increases the fluidity of the membrane. As the temperature increases, longer fatty acid chains with fewer double bonds will be more prevalent in the membrane.