3 9 15 Biochemistry 401 Lecture 26 Fatty Acids Overview Triacylglycerols Catabolism of Triacylglycerol Dietary Sources Endogenous Fatty Acid Oxidation Catabolism of Saturated Fatty Acids Catabolism of Unsaturated Fatty Acids Fatty Acids Overview Fatty acids are hydrocarbon chains that end in carboxylic acid At physiologic pH carboxylic acid is deprotonated to carboxylate Hydrocarbon Chain Carboxylate 16C Saturated Fatty Acid Double bonds kink the hydrocarbon chain 18C Monounsaturated Fatty Acid Fatty acids can have short medium or long hydrocarbon chains They can also have differing degrees of saturation Long saturated fatty acids pack well and so have higher melting temperatures than shorter or than unsaturated fatty acids Three stearates C18 One oleate between two stearates 1 3 9 15 Two means of identifying locations of double bonds C16 0 Saturated Fatty Acid 2 4 6 8 9 1 3 C18 1 cis 9 5 7 Monounsaturated Fatty Acid 1 Numbering from the Carboxylate End identify the double bond location by the number of the carbon in the double bond closer to the carboxylate end C 2 Numbering from the methyl end called the omega end the carbon in the double bond that is closer to the end identifies the location of the double bond In animals even number 16 24 carbons unbranched Most common are 16 and 18 carbon FAs Double bonds are cis not trans Polyunsaturated double bonds are separated by a methylene group Odd branched chain fatty acids are synthesized by bacteria Oddly enough ruminant animal fat contains odd numbered fatty acids 2 3 9 15 Odd numbered and Branched Chain Fatty Acids Odd numbered and branched chain fatty acids are found in bacteria They are rare in animals Bacteria found in the digestive tract of ruminant animals are ingested by these animals and branched chain fatty acids are found in the body fat of these animals Glycerol 3 FA Glycerol Three fatty acids Covalent ester linkage Triacylglycerol Triacylglycerol Diacylglycerol 1 FA Monoacylglycerol 2 FA Triacylglycerols fats High energy fuel Preferred Fuel of Liver Heart Used as fuel by skeletal muscles Most of our stored fuel is triacylglycerol Yields a greater quantity of ATP per gram than Glycogen Highly reduced hydrocarbon FAs Hydrophobic no hydration shell Adipocyte Fats Nucleus Glycerol Three fatty acids Covalent ester linkage 3 3 9 15 Catabolism of dietary fats begins in the small intestine Bile Salts amphipathic derivatives of cholesterol Synthesized in the liver Stored in the gall bladder Released into the small intestine Emulsify TAGs a bile salt blood adipocytes and muscle Glucagon Epinephrine Induce Lipolysis Through Activation of PKA 4 3 9 15 mitochondria Adipocyte Triacylglycerols fats High energy fuel Preferred Fuel of Liver Heart Used as fuel by skeletal muscles Most of our stored fuel is triacylglycerol Yields a greater quantity of ATP per gram than Glycogen Highly reduced hydrocarbon FAs Hydrophobic no hydration shell Fats Nucleus Catabolism of dietary fats begins in the small intestine Bile Salts amphipathic derivatives of cholesterol Synthesized in the liver Stored in the gall bladder Released into the small intestine Emulsify TAGs a bile salt 5 3 9 15 TAGs cannot diffuse through cell membranes FAs are removed through hydrolysis by pancreatic lipase FAs and Monoacylglycerol can enter intestinal mucosal cells blood adipocytes and muscle Glucagon Epinephrine Induce Lipolysis Through Activation of PKA 6 3 9 15 mitochondria Glycerol Can Be Used by the Liver to Synthesize Glyceraldehyde 3 P for Use in Glycolysis or Gluconeogenesis Triose Phosphate Isomerase Oxidation Oxidation of fatty acids occurs in mitochondria Begins with activation of the fatty acid by CoA 7 3 9 15 Two step process occurs on the outer mitochondrial membrane 1 Activation The fatty acid activated by ATP to form acyl adenylate and PPi is released The reaction is driven forward through hydrolysis of PPi and is irreversible 2 Transfer fatty acid is transferred to CoA and AMP is released Fatty Acid Oxidation Occurs in the Mitochondrial Matrix Long chain fatty acids greater than 8 10C must be transported across the inner mitochondrial membrane The activated fatty acid is transferred to carnitine for transport across the inner mitochondrial membrane to the matrix Enzyme Carnitine acyltransferase I Once in the mitochondrial matrix CoA is again attached and carnitine is released Enzyme Carnitine acyltransferase II 8 3 9 15 Because the beta carbon will be oxidized fatty acid degradation is also called the beta oxidation of fatty acids Oxidation of activated saturated fatty acids occurs in the mitochondria in 4 steps 1 Oxidation I 2 Hydration 3 Oxidation II 4 Thiolysis removal of an activated two carbon acetyl unit through addition of Coenzyme A Oxidation reductions require Electron carriers First FAD Next NAD 9 3 9 15 10 3 9 15 Round 1 Round 2 With each round of oxidation one Acetyl CoA is produced Round 3 Double bonds present a problem and require a special enzyme cis 3 Enoyl CoA Isomerase Causes a rearrangement that creates a double bond at C 2 in an isomerization reaction yielding trans 2 Enoyl CoA Can enter oxidation pathway Hydration With monounsaturated fatty acids Oxidation 1 and its FADH are lost Saturated Oxidation 1 Hydration Oxidation 2 Thiolysis 11 3 9 15 Polyunsaturated Fatty Acids present special problems due to its complexity we will not be covering this topic 16C Saturated Fatty Acid How many cycles are needed to break palmitate down completely to Acetyl CoA How many Acetyl CoA produced How many NADH and how many FADH2 produced 12 3 9 15 16C Saturated Fatty Acid How many cycles are needed to break palmitate down completely to Acetyl CoA How many Acetyl CoA produced How many NADH and how many FADH2 produced This is the end of Lecture 26 have a great day 13
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