) (8 pts) Using liver extracts to study the oxidation of fatty acids, you make t
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) (8 pts) Using liver extracts to study the oxidation of fatty acids, you make the following observations: 1) When myristate (14:0) is provided as the substrate, it is completely oxidized to CO2 2) When tridecanoic acid (13:0) is added as the substrate, incomplete oxidation occurs unless CO2 is bubbled through the reaction mixture. 3) The addition of avidin, which binds biotin strongly, prevents complete oxidation of tridecanoic acid under any circumstances, although it has no effect on myristate oxidation. Explain each observation given what you know about fatty acid catabolismExplanation / Answer
1. Myristate is a saturated fatty acid with 14 carbon atoms. It undergoes beta-oxidation in liver cells and gives rise to 7 acetyl-CoA molecules. These acetyl-CoA molecules then enter into tricarboxylic acid (TCA) cycle and completely oxidized to carbon dioxide.
2. Tridecanoic acid is a saturated fatty acid with 13 carbon atoms and is present in milk. It undergoes normal beta-oxidation. However at the end of 6 oxidation steps it gives rise to 3 carbon end product (Propionyl-CoA) as it has odd number of carbons in it. This propionyl Co-A then undergoes carboxylation and gives rise to succinyl Co-A which enters into TCA cycle. Hence carbon dioxide is necessary for complete oxidation of any saturated fatty acid with odd number of carbon atoms in it.
3 The carboxylation of propionyl Co-A to succinyl Co-A is a biotin dependent step. Biotin acts as a co-enzyme and it is necessary. If avidin is added, it binds strongly with biotin and hence blocks its activity involved in carboxylation of propionyl Co-A.
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