BICH 411 1st Edition Lecture 6Outline of Previous LectureI. Review for TestOutline of Current Lecture I. The Citric Acid Cycle overviewII. Reaction 0III. Reaction 1IV. Reaction 2Current Lecture -The next part of metabolism, the Citric Acid Cycle (also called Krebs cycle and TCA cycle), occurs in the mitochondria. It consists of 8 steps (not including step 0, where pyruvate decarboxylates to Acetyl CoA).-Anytime you have an oxidation (oxidative decarboxylation), there has to be a reduction reaction as well. For the TCA cycle, the reduction is of NAD+ to NADH. It is important to note that the concentration of NADH regulates the TCA cycle. -Pyruvate is further oxidized to acetyl CoA (only 2 carbons) so it can enter the TCA cycle. The 3rd carbon is lost as carbon dioxide (CO2). The electrons saved from NADH enter the electron transport pathway in the intermembrane space of the mitochondria. Only a little ATP (1 per cycle) is produced, but multiple NADH’s are produced. (**whenever a dehydrogenase is used, reduction reaction is occurring. Mostly, this signals NADH production.)-pyruvate dehydrogenase complex consists of 3 different enzymes – it’s a very large complex! Just know E1, E2, and E3, but know their individual functions. -reaction 0: pyruvate + NAD+ + CoASH  acetyl CoA + NADH + H+ + CO2, with the help of the pyruvate dehydrogenase complex. This produces 2 electrons that enter the electron transport pathway.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.-Pyruvate is cleaved oxidation to CO2, which regenerates oxaloacetate, and capturing the energy produced. -5 coenzymes are required the oxidative decarboxylation of pyruvate. The reaction that converts pyruvate to acetyl CoA is a reaction that breaks C-C bonds. It’s irreversible, with a –ΔG’=-33.4 kJ/mol. E1 transfers the hydroxyethyl group from pyruvate to TPP, forming HETPP (hydroxyethyl TPP). E2transfers the hydroxyethyl group to lipoic acid where it is then oxidized to form acetyl dihydrolipoate. E3 facilitates the transfer of the hydroxyethyl group to CoA. NAD+ picks up a hydrogen, reoxidizing lipoic acid, and reducing NAD+ to NADH + H+. **E3 restores E2 through it’sreoxidation of lipoic acid. -cofactors: 1.TPP is the first cofactor necessary for the pyruvate dehydrogenase complex. 2. Riboflavin (found in FAD) transfers electrons in the complex. 3. Niacin (in NAD) transfers hydride in the complex. 4. Pantothenate (in CoA). 5. Lipoic Acid which carries electrons, and bridges the complex with it’s long arms. **The reason why we use FAD, is that it has a greater reduction potential than lipoic acid and NAD+-Coenzyme A (CoA) activates the acyl groups for transfer through nucleophilic attack. It also activates the alpha hydrogen to be removed as a proton. Lipoic acid is bound to enzymes with the epsilon NH2 group of lysine side chains. **review the mechanism of reaction 0 in the slides***-Reaction 1: Citrate synthase initiates the cycle. The alpha carbon of the acetyl group in acetyl CoA is deprotonated. The resulting carbanion is a nucleophile which attacks oxaloacetate, forming citryl-CoA. Citryl-CoA undergoes thioester hydrolysis to produce citrate. NADH and Succinyl CoA inhibit here. Citrate synthesis has the largest –ΔG, making it the most energetically favorable. This is a reaction that makes C-C bonds, through Claisen ester condensation (oxaloacetate is the feeder). **Review this mechanism**-Reaction 2: CitrateIsocitrate. Aconitase changes citrate to isocitrate (with a secondary –OH), through an isomerization reaction. (dehydration then hydration) **The reaction removes the pro-R H from the pro-R arm of citrate. (****Pro-s arm came from acetate****)Label your carbons so you can keep track of which arm is which. **Review mechanism in the slides****It’s important to note that fluoroacetate blocks the TCA cycle. It blocks the cycle by inhibiting aconitase, preventing the isomerization of citrate. It’s very poisonous!**Binding of Fe2+ activates aconitase (need iron). It accepts the electron pair from the –OH group. This makes a better leaving