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Citric Acid Cycle Chapter
- 1. Principles of Biochemistry Fourth Edition Chapter 13 The Citric Acid Cycle Copyright © 2006 Pearson Prentice Hall, Inc. Horton • Moran • Scrimgeour • Perry • Rawn
- 2. Aerobic RespirationAerobic Respiration Glycolysis occurs in theGlycolysis occurs in the cytosolcytosol All other stages in theAll other stages in the mitochondriamitochondria
- 10. Mammalian
- 14. Acetil CoA para síntesis de ácidos grasos
- 16. Bacterias, levaduras, protistas y plantas
- 18. Acetyl CoA accumulation with low oxaloacetate during starvation or diabetes
- 20. Principles of Biochemistry Fourth Edition Chapter 14 Electron Transport and ATP Synthesis Copyright © 2006 Pearson Prentice Hall, Inc. Horton • Moran • Scrimgeour • Perry • Rawn
- 21. Aerobic RespirationAerobic Respiration Glycolysis occurs in theGlycolysis occurs in the cytosolcytosol All other stages in theAll other stages in the mitochondriamitochondria
- 33. Efecto Pasteur en condiciones anaeróbicas
- 34. Principles of Biochemistry Fourth Edition Chapter 12 Gluconeogenesis, The Pentose Phosphate Pathway, and Glycogen Metabolism Copyright © 2006 Pearson Prentice Hall, Inc. Horton • Moran • Scrimgeour • Perry • Rawn
- 43. Regulation of glycolysis and gluconeogenesis in the liver
- 44. Precursores para gluconeogénesis (lactato, amino ácidos, glycerol y **acetilCoA)
- 48. Synthesis of glycogen in eukaryotes
- 58. Acetyl CoA accumulation with low oxaloacetate during starvation or diabetes
Editor's Notes
- Figure 13.1 Reactions of the pyruvate dehydrogenase complex. The lipoamide prosthetic group (blue) is attached by an amide linkage between lipoic acid and the side chain of a lysine residue of This prosthetic group is a swinging arm that carries the two-carbon unit from the pyruvate dehydrogenase active site to the dihydrolipoamide acetyltransferase active site. The arm then carries hydrogen to the dihydrolipoamide dehydrogenase active site.
- Figure 13.3 Citric acid cycle. For each acetyl group that enters the pathway, two molecules of CO2 are released, the mobile coenzymes NAD+ and ubiquinone (Q) are reduced, one molecule of GDP (or ADP) is phosphorylated, and the acceptor molecule (oxaloacetate) is re-formed.
- Figure 13.10 ATP production from the catabolism of one molecule of glucose by glycolysis, the citric acid cycle, and reoxidation of NADH and QH2 The complete oxidation of glucose leads to the formation of up to 32 molecules of ATP.
- Figure 13.11 Regulation of the pyruvate dehydrogenase complex. Accumulation of the products acetyl CoA and NADH decreases flux through the reversible reactions catalyzed by E2 and E3.
- Figure 13.12 Regulation of the mammalian pyruvate dehydrogenase complex by phosphorylation of the E1 component. The regulatory kinase and phosphatase are both components of the mammalian complex. The kinase is activated by NADH and acetyl CoA, products of the reaction catalyzed by the pyruvate dehydrogenase complex, and inhibited by ADP and the substrates pyruvate, NAD+, and HS–CoA. Dephosphorylation is stimulated by elevated levels of Ca2+.
- Figure 13.13 Routes leading to and from the citric acid cycle. Intermediates of the citric acid cycle are precursors of carbohydrates, lipids, and amino acids, as well as nucleotides and porphyrins. Reactions feeding into the cycle replenish the pool of cycle intermediates.
- Acetyl-CoA is produced in mitochondria through the metabolism of fatty acids and the oxidation of pyruvate to acetyl-CoA. When ATP is needed, this acetyl-CoA can enter the Krebs cycle to drive oxidative phosphorylation. When ATP supplies are abundant, the acetyl-CoA can be diverted to other purposes like energy storage in the form of fatty acids. The biosynthesis of fatty acids from this acetyl-CoA cannot take place directly however, since it is produced inside mitochondria while fatty acid biosynthesis occurs in the cytosol. Also, there is not a mechanism that directly transports acetyl-CoA out of mitochondria. To be transported, the acetyl-CoA must be chemically converted to citric acid using a pathway called the tricarboxylate transport system. Inside mitochondria, the enzyme citrate synthase joins acetyl-CoA with oxaloacetate to make citrate. This citrate is transported from the mitochondria to the cytosol, thus transporting the acetyl-CoA in the form of citrate. Once in the cytosol, the citrate is converted back to oxaloacetate, which is then reduced to malate. Malate can be oxidized to pyruvate by the malic enzyme, with production of NADPH as well that can contribute to fatty acid biosynthesis. Pyruvate can be reimported back into the mitochondria. Alternatively, malate can be transported itself back into the mitochondria and used to produce NADH once inside mitochondria
- Figure 13.14 Glyoxylate pathway. Isocitrate lyase and malate synthase are the two enzymes of the pathway. When the pathway is functioning, the acetyl carbon atoms of acetyl CoA are converted to malate rather than oxidized to CO2. Malate can be converted to oxaloacetate which is a precursor in gluconeogenesis. The succinate produced in the cleavage of isocitrate is oxidized to oxaloacetate to replace the four-carbon compound consumed in glucose synthesis.
- Figure 16.19 -Oxidation of saturated fatty acids. One round of -oxidation consists of four enzyme-catalyzed reactions. Each round generates one molecule each of QH2, NADH, acetyl CoA, and a fatty acyl CoA molecule two carbon atoms shorter than the molecule that entered the round. (ETF is the electron-transferring flavoprotein, a water-soluble protein coenzyme.)
- Figure 14.2 Structure of the mitochondrion. The outer mitochondrial membrane is freely permeable to small molecules but the inner membrane is impermeable to polar and ionic substances. The inner membrane is highly folded and convoluted forming structures called cristae. The protein complexes that catalyze the reactions of membrane-associated electron transport and ATP synthesis are located in the inner membrane. (a) Illustration. (b) Electron micrograph: longitudinal section from bat pancreas cell.
- Figure 14.2 Structure of the mitochondrion. The outer mitochondrial membrane is freely permeable to small molecules but the inner membrane is impermeable to polar and ionic substances. The inner membrane is highly folded and convoluted forming structures called cristae. The protein complexes that catalyze the reactions of membrane-associated electron transport and ATP synthesis are located in the inner membrane. (a) Illustration. (b) Electron micrograph: longitudinal section from bat pancreas cell.
- Figure 14.1 Overview of membrane-associated electron transport and ATP synthesis in mitochondria. A proton concentration gradient is produced from reactions catalyzed by the electron transport chain. As electrons from reduced substrates flow through the complexes, protons are translocated across the inner mitochondrial membrane from the matrix to the intermembrane space. The free energy stored in the proton concentration gradient is utilized when protons flow back across the membrane via ATP synthase; their reentry is coupled to the conversion of ADP and Pi to ATP.
- Figure 14.14 The knob-and-stalk structure of ATP synthase. (a) The F1 component is on the inner face of the membrane. The F0 component, which spans the membrane, forms a proton channel at the a–c interface. The passage of protons through this channel causes the rotor (shaded) to rotate relative to the stator. The torque of these rotations is transmitted to F1 where it is used to drive ATP synthesis. (b) Molecular structure of the rotor and a portion of the stator of ATP synthase of Saccharomyces cerevisiae. The study of many molecular structures like this, based on X-ray crystallography, assisted in deduction of the complete model shown in (a). [PDB 1QO1].
- Figure 14.16 Demonstration of the rotation of a single molecule of ATP synthase. 33 complexes were bound to a glass coverslip, and the g subunit was attached to a long fluorescent protein arm. The arms on the molecules rotated when ATP was added. [Adapted from Noji, H., Yasuda, R., Yoshida, M., and Kinosita, K., Jr. (1997). Direct observation of rotation of F1-ATPase. Nature 386:299–302.]
- Figure 14.15 Binding change mechanism of ATP synthase. The different conformations of the three catalytic sites are indicated by different shapes. ADP and Pi bind to the yellow site in the open conformation. As the shaft rotates in the counter-clockwise direction (viewed from the cytoplasmic/matrix end of the F1 component), the yellow site is converted to a loose conformation where ADP and Pi are more firmly bound. Following the next step of the rotation, the yellow site is converted to a tight conformation and ATP is synthesized. Meanwhile, the site that had bound ATP tightly has become an open site, and a loose site containing other molecules of ADP and Pi has become a tight site. ATP is released from the open site, and ATP is synthesized in the tight site.
- Figure 12.1 Comparison of gluconeogenesis and glycolysis. There are four metabolically irreversible reactions of gluconeogenesis (blue). These are the reactions that are catalyzed in the reverse direction by three different enzymes in glycolysis (red). Both pathways include a triose stage and a hexose stage. Two molecules of pyruvate are therefore required to produce one molecule of glucose.
- Figure 12.1 Comparison of gluconeogenesis and glycolysis. There are four metabolically irreversible reactions of gluconeogenesis (blue). These are the reactions that are catalyzed in the reverse direction by three different enzymes in glycolysis (red). Both pathways include a triose stage and a hexose stage. Two molecules of pyruvate are therefore required to produce one molecule of glucose.
- Figure 12.1 Comparison of gluconeogenesis and glycolysis. There are four metabolically irreversible reactions of gluconeogenesis (blue). These are the reactions that are catalyzed in the reverse direction by three different enzymes in glycolysis (red). Both pathways include a triose stage and a hexose stage. Two molecules of pyruvate are therefore required to produce one molecule of glucose.
- Figure 12.4 Regulation of glycolysis and gluconeogenesis in the liver. Substrate cycles occur between fructose 6-phosphate and fructose 1,6-bisphosphate and between phosphoenolpyruvate and pyruvate. Changing the activity of any of the enzymes in the substrate cycles can affect not only the rate of flux but also the direction of flux toward either glycolysis or gluconeogenesis. The net effect is enhanced regulation at the expense of the hydrolysis of ATP.
- Figure 12.2 Cori cycle: glucose catabolism to L-lactate in peripheral tissues, delivery of lactate to the liver, formation of glucose from lactate in the liver, and delivery of glucose back to peripheral tissues.
- Figure 12.3 Gluconeogenesis from glycerol. Glycerol 3-phosphate can be oxidized in reactions catalyzed by either of two dehydrogenases; both reactions yield reduced coenzymes. The liver contains both dehydrogenases, so both reactions can occur there.
- Figure 13.14 Glyoxylate pathway. Isocitrate lyase and malate synthase are the two enzymes of the pathway. When the pathway is functioning, the acetyl carbon atoms of acetyl CoA are converted to malate rather than oxidized to CO2. Malate can be converted to oxaloacetate which is a precursor in gluconeogenesis. The succinate produced in the cleavage of isocitrate is oxidized to oxaloacetate to replace the four-carbon compound consumed in glucose synthesis.
- Figure 12.10 Synthesis of glycogen in eukaryotes.
- Figure 12.11 Addition of a glucose residue to the nonreducing end of a glycogen molecule, catalyzed by glycogen synthase.
- Figure 12.15 Effects of hormones on glycogen metabolism. (a) The binding of glucagon to its receptors or the binding of epinephrine to -adrenergic receptors stimulates glycogen degradation via protein kinase A. (b) The binding of epinephrine to 1-adrenergic receptors stimulates protein kinase C, which inactivates insulin receptors. Activated enzymes have a green background.
- Figure 12.16 Activation of glycogen phosphorylase and inactivation of glycogen synthase. Phosphorylation reactions catalyzed by protein kinase A increase glycogen degradation. A green background indicates activated enzymes; a red background indicates inactivated enzymes. Green arrows signify activation; red arrows signify inactivation.
- Figure 12.17 Activation of glycogen synthase and inactivation of glycogen phosphorylase. Hydrolysis of phosphate monoester bonds catalyzed by protein phosphatase-1 increases glycogen synthesis.
- Figure 12.15 Effects of hormones on glycogen metabolism. (a) The binding of glucagon to its receptors or the binding of epinephrine to -adrenergic receptors stimulates glycogen degradation via protein kinase A. (b) The binding of epinephrine to 1-adrenergic receptors stimulates protein kinase C, which inactivates insulin receptors. Activated enzymes have a green background.
- Figure 12.20 Five phases of glucose homeostasis. The graph, based on observations of a number of individuals, illustrates glucose utilization in a 70 kg man who consumed 100 g of glucose and then fasted for 40 days.
- Figure 13.13 Routes leading to and from the citric acid cycle. Intermediates of the citric acid cycle are precursors of carbohydrates, lipids, and amino acids, as well as nucleotides and porphyrins. Reactions feeding into the cycle replenish the pool of cycle intermediates.
- Figure 12.13 Binding and catalytic sites on glycogen phosphorylase.
- Figure 12.14 Degradation of glycogen. Glycogen phosphorylase catalyzes the phosphorolysis of glycogen chains, stopping four residues from an -(1-->6) branch point and producing one molecule of glucose 1-phosphate for each glucose residue mobilized. Further degradation is accomplished by the two activities of the glycogen-debranching enzyme. The 4--glucanotransferase activity catalyzes the transfer of a trimer from a branch of the limit dextrin to a free end of the glycogen molecule. The amylo-1,6-glucosidase activity catalyzes hydrolytic release of the remaining -(1-->6)-linked glucose residue.
- Figure 12.18 Regulation of glycogen metabolism by glucose in the liver. Inhibition of protein phosphatase-1 by glycogen phosphorylase a is relieved when glucose binds to the phosphorylase. Glycogen phosphorylase is then inactivated, and glycogen synthase is activated.