lecture 3r

lecture 3r - BIS 103 - #3 - Tricarboxylic acid (TCA) or...

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Unformatted text preview: BIS 103 - #3 - Tricarboxylic acid (TCA) or citric acid or Krebs cycle - Outline Phase 1 Condensation of oxaloacetate (OAA) and acetyl-CoA to form citrate (6 C) Oxidative decarboxylations to yield 2 CO 2 per acetyl-CoA Formation of 2 NADH and GTP and a 4 C compound, succinate Phase 2 Conversion of succinate to yield OAA so that the cycle can continue 1 FADH 2 and 1 NADH produced Summary: 8 steps in phases 1 and 2; a cycle where 2 CO 2 are released 3 NADH + H + , 1 FADH 2 , and 1 GTP are produced; oxidation of NADHs and FADH 2 will yield 11 ATPs. The TCA cycle is found in the mitochondria of eukaryotic cells. Eukaryotic cells may have evolved from a symbiotic relationship between a prokaryotic form and an ancient eukaryotic form. There was more energy available for the cell when an aerobic prokaryotic form integrated Into an anaerobic eukaryotic form. The mitochondria has its own DNA and protein synthesizing system that resembles a prokaryotic system and is distinct from the nuclear directed system. Although glycolysis was a linear pathway, the reactions in the TCA cycle are cyclical. Glucose 2 pyruvate 2 acetyl-CoA + 2 CO 2 glycolysis PDH complex TCA cycle 4 CO 2 Glycolysis = 8 ATPs PDH complex = 6 ATPs TCA cycle = 24 ATPs Under aerobic conditions: The major functions of the TCA cycle are to oxidize carbon compounds in order to obtain energy (ATP) and also to provide carbon skeletons for anabolic reactions. TCA plays a major role in metaboiism Anabolic reactions 1. Glucose biosynthesis (OAA) 2. Lipid biosynthesis (acetyl-CoA) 3. Amino acid biosynthesis ( -KG, OAA) 4. Purine and pyrimidine biosynthesis Catabolic reacttions 1. Oxidation of acetyl-CoA to CO 2 2. Amino acid degradation (obtain -KG, OAA) 3. Oxidation of odd chain fatty acids to succinyl-CoA 4. Degradation of Ile, Met, and Val to succinyl-CoA What are the major functions of the TCA or citric acid cycle? 1. The production of energy by oxidation of acetyl-CoA. The products of the TCA cycle include NADH + H + and FADH 2 that can be oxidized by the electron transport system to produce ATP. One of the steps also results in the production of GTP. 2. To provide carbon skeletons for the synthesis of various compounds such as amino acids, nucleotides, and heme. 3. Also during gluconeogenesis, the TCA cycle provides oxaloacetate, which can be converted to phosphoenolpyruvate (PEP). The TCA cycle is the main pathway for generating energy yielding factors under aerobic conditions. TCA cycle is present in the mitochondria. Intermediates of the TCA cycle that are used for the synthesis of important compounds: Citrate : fatty acids, steroids -Ketoglutarate : glutamic acid family of amino acids, purines Succinyl-CoA : porphyrins, hemes Oxaloacetate: aspartic acid family of amino acids; pyrimidines Compounds that are fed into the TCA cycle as acetyl-CoA carbohydrates fatty acid degradation product amino acid degradation product General features of TCA cycle:...
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lecture 3r - BIS 103 - #3 - Tricarboxylic acid (TCA) or...

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