BMB 462 Lecture 11 Outline of Last Lecture I. Overview of Fatty Acid AnabolismII. Activation and Regulation by Acetyl-CoA Carboxylase (ACC)III. Coordinating Regulation of synthesis and DegradationIV. Synthesis CarriersV. Synthesis enzymes and cofactorsVI. Compare and Contrast synthesis vs. degradationVII. Locations of various processesVIII. Sources of electron carriersIX. Synthesis transporters and enzymesOutline of Current Lecture I. Elongation and Desaturation of fatty acidsII. Mixed function oxidasesIII. Sources of Glycerol 3-phosphateIV. Synthesis of Phosphatidic Acid and TriacylglycerolV. Strategy for membrane lipid synthesisVI. Phosphatidylethanolamine and PhosphatidylcholineCurrent LectureConcepts to remembers from previous courses/lectures:- Mixed function oxidases, i.e. Cytochrome P450 - using e- from substrate but still need 2nd source of e- to get all that is necessaryI. Elongation and Desaturation of fatty acidsa. Elongation and desaturation can occur in any order, though it’s more common to start with elongationb. Mostly occurs in the smooth ER, some elongation/desaturation takes place in themitochondriac. Elongation – the cell adds 2 carbons at a time to the carboxyl end of the moleculei. It essentially involves the same 4 steps as fatty acid synthesis (condensation, reduction, dehydration, and a second reduction)These notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.d. Desaturation: double bonds are introduced 3 carbons aparti. Desaturase always initially adds a double bond to carbon 9 in humans1. Animals can only add bonds at positions 4, 5, 6, and 9e. Essential Fatty Acids – because humans can only add double bonds at specific positions in the carbon chain, there are fatty acids that can’t be synthesized and must be ingested in the diet.i. i.e. linoleate - Humans can't add double bond to position 12 (but plants can) so linoleate is an essential fatty acid and must be in diet.ii. It's important in making arachadonate (precursor for eicosanoids - signaling molecules)iii. EPA and DHA (omega-3 fatty acids)II. Mixed function oxidasesa. i.e. Fatty acyl-CoA Desaturasei. It uses molecular oxygen as electron donor (need 4 e- to reduce oxygen)ii. e- come from: 2 from 2 carbons in fatty acid - go to oxygen to make water1. The remaining 2 come from NADPH to make the 2nd water.III. Sources of Glycerol 3-phosphatea. Glycerol 3-phosphate is the backbone for phosphatidic acid.b. The cell gets glycerol from TAG breakdowni. Glycerol is phosphorylated by glycerol kinase for glycerol-3-phosphatec. Another route is to reduce the intermediate dihydroxyacetone phosphatei. NADH is source of e-ii. Also get glycerol-3-phosphateIV. Synthesis of Phosphatidic Acid and Triglycerola. Phosphatidic acidi. Phosphatidic acid is common intermediate in synthesis of lipids doesn't exist in any great quantity free in the cell (intermediate in synthesis of TAG and phosphoglycerols)ii. Need to add 2 Fatty Acids to get from glycerol 3-phosphate to phosphatidic acid. They’re esterified to the carboxylate.iii. Activated Fatty Acids1. It is not favourable to just add carboxylate to hydroxyl. To aid in the reaction, the cell activates them by adding CoAs. a. CoA added by acyl-CoA synthase (same enzyme from breakdown)2. CoA acts as an e- sink to make the Carbon in the thioester bond more open to reaction. This happens twiceiv. Transfer of Fatty Acids to Hydroxyls1. Acyl transferases are what actually attach fatty acids to molecule.b. Triacylglycerolsi. Dephosphorylate Phosphatidic Acid1. Need to add a third fatty acid but currently have a phosphate group in the way so need to dephosphorylate via phosphatases2. Phosphatidic acid phosphatase dephosphorylates to make diacylglycerol and then use acyl transferase again to transfer another activated FA to 3rd hydroxylii. The fatty acid is then transferred to the OH via acyl transferaseV. Strategy for membrane lipid synthesisa. Both glycerophospholipids and sphingolipids are synthesized by first synthesizing the backbone, then adding the fatty acids, then the head group, and finally altering or exchanging the head group as needed.b. Attachment of the glycerophospholipid head groupi. The backbone is made from glycerol1. To attach the head group, the glycerol needs to be activated (thereis a negative ΔG when breaking down fatty acids, and the rearrangement results in a release of free E). 2. The cell withdraws e- from components to make the backbone more electrophilic and open to attack and make better leaving groups – (activation does all this)ii. CTP is often used to activate alcohol head groups - i.e. choline, ethanolamineiii. UTP is used to activate sugar head groups, at least in mammals.iv. Start with phosphorylated head group and NTP. The activated head group will have 2 phosphates attached to it as well as ribose and base (CDP or UDP depending on head group; CDP/UDP linked intermediate is active form)v. Release pyrophosphate, which is converted to 2 phosphates. 1. This is a very negative ΔG, so it releases a lot of free energy, which is needed to make the rest of the reaction move forward.vi. Strategies for activation – you can either activate head group and attach to diacylglycerol or activate the phosphatidic acid and then attach the alcohol to that.1. Strategy 1. Phosphatidate activation: Produce CDP-diacylglycerol, and then the alcohol head group attacks the activated CDP portion. CDP leaves and OH head group can bind2. Strategy 2. Head Group Activation: This happens in the opposite way; start with CDP-head group which gets attacked by OH on diacylglycerolVI. Phosphatidylethanolamine and Phosphatidylcholinea. Strategy II is used to make phosphatidylethanolamine (PE) and phosphatidylcholine (PC) in mammalsb. To get Phosphatidylserine (PS), take PE, break off ethanolamine and add serinec. Getting PC from PE via methylation - methyl transferases add the methyl group. i. AdoMet (aka SAM) donates methyl group – it is an important coenzyme for adding the
View Full Document
Unlocking...