Lecture 33Outline of Last Lecture I. The Citric Acid CycleA. Other Names for the CycleB. Conditions to FunctionII. An Overview of the Citric Acid CyleIII. The Citric Acid Cycle EquationIV. Where the TCA Cycle Occurs Outline of Current Lecture I. MitochondriaII. Pyruvate Dehydrogenase ComplexIII. Steps of the Citric Acid CycleCurrent Lecture This lecture continues on with the steps of the citric acid cycle. The citric acid cycle occurs in the mitochondrion in eukaryotes, specifically the mitochondrial matrix. The mitochondria has an inner and out membrane. The outer membrane is freely permeable to small molecules and ions. The inner membrane contains the matrix and is impermeable to small ions. In prokaryotes, the citric acid cycle occurs in the cytoplasm. The product of glycolysis that is need for the citric acid cycle is pyruvate. Pyruvate has to get into the mitochondrial matrix somehow. The pyruvate dehydrogenase complex bridges this gap. This occurs in the mitochondria of eukaryotes and the cytosol of prokaryotes. Pyruvate is able to cross 2 membranes through thisreaction. The pyruvate dehydrogenase complex is a quaternary structure consisting of a cluster of several enzymes. Pyruvate is able to become Acetyl- CoA through the complex. Acetyl-CoA is a better enzyme binding site. The full equation for this reaction is given below. CoA-SH stands for Coenzyme A. Coenzyme A contains a free thiol group which can form thioesters. Pyruvate + CoA-SH + NAD+ → acetyl-CoA + CO2 + NADH + H+Now that acetyl-CoA has been formed, the official citric acid cycle process can begin. The steps of this process are listed below.1. Acetyl-Co A has oxaloacetate and water added to it. This forms citrate, CoA-SH, and a hydrogen ion. This reaction can only proceed forwards. The oxaloacetate comes from the previous citric acid cycle, and is the final end product formed. Citrate synthase is the enzyme catalyzing this reaction.2. Citrate goes through a reversible reaction and forms isocitrate. An enzyme-bound intermediate is formed in between these steps, which is cis-Aconitate + a water molecule. This is an isomerization reaction catalyzed by aconitase. BCHM 307 1nd Edition3. Isocitrate has NAD+ added to form alpha-ketoglutarate, carbon dioxide, and NADH. This is a redox reaction, with NAD+ being reduced. Isocitrate dehydrogenase catalyzes this reaction.4. Alpha-ketoglutarate has CoASH and NAD+ added to it. This forms succinyl-CoA, carbon dioxide, NADH, and a hydrogen ion. This is a redox reaction catalyzed by alpha-ketoglutarate dehydrogenase complex. 5. Succinyl-CoA had GDP and inorganic phosphate added to it. This is a reversal reaction. It forms succinate, CoASH, and GTP. Succinate is perfectly symmetric molecule. Succinyl-CoA synthetase catalyzes this reaction.6. Succinate has FAD added to it. This reversible reaction forms fumarate and FADH2. This is a redox reaction catalyzed by succinate dehydrogenase. Succinate dehydrogenase is an insoluble enzyme associated with the inner mitochondrial membrane. 7. Fumarate has water added to form L-malate. This is a reversible reaction. This reaction is catalyzed by fumerase. 8. Malate and NAD+ are combined to form oxaloacetate, NADH, and a hydrogen ion. This is the final step of the citric acid cycle. This is an example of a redox reaction and it is a reversible reaction catalyzed by malate
View Full Document
Unlocking...