1 CHAPTER 4: THE CITRIC ACID AND OXIDATIVE PHOSPHORYLATION INTERNATIONAL UNIVERSITY SCHOOL OF BIOTECHNOLOGY BIOCHEMISTRY 2 Learning objectives 1. To understand the intermediates in CAC 2. The ATPs produce in CAC 3. The CO2 is released in CAC 4. The electrons are transferred in the electron transport chain 5. The oxidative phosphorylation 3 Content Citric acid cycle Introduction Cellular location Catabolism Anabolism & catabolism Sources of acetyl-CoA Fatty acid –aminoacid- monosaccharides 4 Content Reactants & products Cyclical reaction pathway Fate of acetyl CoA carbon regulation: inhibition Energetics Anaerobic Anaplerotic reactions Oxidative phoshorylation Introduction Mitochondrial anatomy Shuttle system Introduction to the transport chain Comlex I- comlex II- comlex III and Cytochrome C- comlex IV 5 Citric Acid Cycle INTRODUCTION The citric acid cycle is a central metabolic pathway that completes the oxidative degradation of fatty acids, amino acids, and monosaccharides. During aerobic catabolism, these biomolecules are broken down to smaller molecules that ultimately contribute to a cell’s energetic or molecular needs. 6 FIG. 01: Citric acid cycle is the central metabolic pathway 7 INTRODUCTION Early metabolic steps, including glycolysis and the activity of the pyruvate dehydrogenase complex, yield a two-carbon fragment called an acetyl group, which is linked to a large cofactor known as coenzyme A (or CoA). It is during the citric acid cycle that acetyl-CoA is oxidized to the waste product, carbon dioxide, along with the reduction of the cofactors NAD+ and ubiquinone. 8 FIG. 02: Early catabolic pathway 9 FIG. 03: Citric acid cycle is the central metabolic pathway 10 INTRODUCTION The citric acid cycle serves two main purposes: 1.To increase the cell’s ATP-producing potential by generating a reduced electron carriers such as NADH and reduced ubiquinone; and 2.To provide the cell with a variety of metabolic precursors. [...]... carriers and their role in coupling the citric acid cycle to downstream reactions that produce ATP; Describe the amphibolic character of the citric acid cycle; and Understand the reactions that replenish citric acid cycle intermediates 13 CELLULAR LOCATION Both prokaryotic and eukaryotic cells use the citric acid cycle to help meet their energetic and molecular needs In respiring prokaryotes, the citric acid. ..FIG 04: Main purposes of CAC 11 INTRODUCTION Be able to describe the sources of acetyl groups that enter the citric acid cycle; Trace the conversion of substrates to products through each of the citric acid cycle’s eight reactions and understand how flux through the cycle is regulated; Understand the energetic output of the citric acid cycle; 12 INTRODUCTION Describe the role of the reduced... and degrading molecules are considered amphibolic Amphi is a Greek prefix meaning both 23 FIG 10: The CAC is amphibolic 24 SOURCES OF ACETYL-CoA 25 The skeleton drawings of the monosaccharide glucose, the fatty acid palmitic acid, and the amino acids lysine and glutamate are depicted These molecules are degraded to a common compound called acetyl-CoA, the initiator of the citric acid cycle Select the. .. in CAC are the precursors for biosynthesis 22 ANABOLISM AND CATABOLISM Many citric acid cycle intermediates serve the cell as both reaction precursors and reaction products For example, a-ketoglutarate may act as a precursor for amino acids in an anabolic pathway, or it may be catabolized to carbon dioxide during the reactions of the citric acid cycle As such, the citric acid cycle is neither purely... ultimately enters the citric acid cycle as acetyl-CoA Then consider how the efficiency of metabolism would change if a common product of carbohydrate, fatty acid, and amino acid catabolism did not exist Fatty Acids Many different fatty acids exist, although their structures can be generalized as a carboxylic acid with a long, hydrocarbon tail Palmitate is an example of a sixteen-carbon fatty acid When a... acid cycle takes place in the cytosol In eukaryotic cells, such as the cells of the human body, the cycle takes place within the mitochondrial matrix 14 FIG 05: CAC can be found in both prokaryote and eukaryote 15 FIG 06: Matrix is where the CAC happens 16 CATABOLISM The reactions of the citric acid cycle oxidize acetylCoA’s acetyl group to two molecules of carbon dioxide During the reaction cycle, electrons... needs increase, free fatty acids enter the mitochondrion where the degradative reactions called b oxidation ensue A fatty acid shortened by two carbon atoms plus a free acetyl-CoA molecule results from each round of b oxidation Acetyl-CoA initiates the citric acid cycle 26 Amino Acids Examine the structures of glutamate and lysine Recall that an amino acid consists of an amino and a carboxyl group at... side chain In the case of starvation, protein degradation increases and the free amino acids that result may be used as a source of metabolic fuel Alternatively, if an organism’s intake of free amino acids exceeds its protein-building needs, the free amino acids are metabolized, for there is no storage mechanism for excess amino acids 27 Amino Acids Typically, the amino group of an amino acid is removed... dioxide Acetyl-CoA initiates the citric acid cycle 31 FIG 11: acetyl-CoA is the initiator of CAC 32 REACTANTS AND PRODUCTS Acetyl-CoA is further oxidized in the citric acid cycle As you learn each step in the reaction cycle, keep in mind that additional substrates are necessary to complete one full turn of the reaction cycle, including one GDP, one inorganic phosphate, three NAD+, and one ubiquinone, commonly... downstream reaction pathways that generate ATP, the energy currency of the cell 17 CATABOLISM Note that one high-energy nucleoside triphosphate is generated directly from the reaction cycle Because acetyl-CoA is broken down to smaller molecules during the citric acid cycle, the citric acid cycle is described as catabolic 18 FIG 07: The products from CAC 19 ANABOLISM AND CATABOLISM In addition to catabolizing . regulated; Understand the energetic output of the citric acid cycle; 13 INTRODUCTION Describe the role of the reduced electron carriers and their role in coupling the citric acid cycle to downstream. groups that enter the citric acid cycle; Trace the conversion of substrates to products through each of the citric acid cycle’s eight reactions and understand how flux through the cycle is regulated;. 1 CHAPTER 4: THE CITRIC ACID AND OXIDATIVE PHOSPHORYLATION INTERNATIONAL UNIVERSITY SCHOOL OF BIOTECHNOLOGY BIOCHEMISTRY 2 Learning objectives 1. To understand the intermediates