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cell molec

by: Gabriela Montalvo

cell molec BIL 255

Gabriela Montalvo

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About this Document

krebs cycle notes
Cellular and Molecular Biology
Dr. Baker
Cell Molec
75 ?




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This 2 page Bundle was uploaded by Gabriela Montalvo on Tuesday February 16, 2016. The Bundle belongs to BIL 255 at University of Miami taught by Dr. Baker in Fall. Since its upload, it has received 31 views. For similar materials see Cellular and Molecular Biology in Biology at University of Miami.


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Date Created: 02/16/16
AlsoknownastheKrebscycleorthetricarboxylicacidcycle,the citric acid cycle is at the center of cellular metabolism. It plays a TheStructuresofthe starring role in both the process of energy production and biosynthesis. The cycle finishes the sugar-breaking job started in glycolysis and fuels the production of ATP in the process. It is also a central hub in biosynthetic reactions, providing CitricAcidCycle intermediates that are used to build amino acids and other molecules. Citric acid cycle enzymes are found in all cells that use oxygen, and even in some cells that don't. Acetyl-CoA This metabolic pathway is illustrated using protein structures from the Protein Data Bank. D. Voet, J. G. Voet, C. W. Pratt. (2002), John Wiley & Sons, Inc., New York, NY. Oxaloacetate Citrate L-Malate 1 Isocitrate 8 2 3 Fumarate 7 4 α-Ketoglutarate 6 5 Succinate Succinyl-CoA EightReactions The eight reactions of the citric acid cycle use the small molecule oxaloacetate as a catalyst. The cycle starts by addition of an acetyl group to oxaloacetate, then, over the course of eight steps, the acetyl group is completely broken apart, finally restoring the oxaloacetate molecule for another round. • PowerhouseofEnergy Thecitricacidcycleprovideselectronsthatfueltheprocessofoxidativephosphorylation–ourmajorsourceofATPandenergy.Astheacetylgroupisbroken down, electrons are stored in the carrier NADH and delivered to the large protein complexes that generate the proton gradient that powers ATP synthase. TheEnzymesoftheKrebsCycle 7 Fumarase 8 MalateDehydrogenase 1 CitrateSynthase The seventh step is performed by The final step recreates oxaloacetate, transfer- The cycle gets started with the enzyme citrate fumarase, which adds a water mole- ring electrons to NADH in the process. synthase. The pyruvate dehydrogenase complex cule to get everything ready for the Malate dehydrogenase is found in both the h as previously connected an acetyl group to the final step of the cycle. mitochondrion and the cytoplasm, forming part of a shuttle that transports electrons carrier coenzyme A, which holds it in an activated form. Citrate synthase pops off the acetyl group PDB ID:1fuo across the mitochondrial membrane. and adds it to oxaloacetate, forming citric acid. PDB ID:1mld PDBID:1cts 6 Succinate Dehydrogenase Inthesixthstep,succinate 2 Aconitase dehydrogenase, found in the membrane, links its The citrate formed in the first step is a bit too citric acid cycle task di- stable, so the second step moves an oxygen atom to create a more reactive isocitrate molecule. rectlytotheelectrontrans- Aconitase performs this isomerization reaction, port chain. It extracts hydrogenatomsfromsuc- with the assistance of an iron-sulfur cluster. cinate and transfers them PDB ID:7acn firsttothecarrierFADand finally to the mobile elec- tron carrier ubiquinone. PDBID:1nek 3 IsocitrateDehydrogenase The real work begins in the third step of the cycle. Isocitrate dehydrogenase, removes one of the carbon atoms, forming carbon dioxide, and transfers electrons to NADH. PDBID: 3blw 4 2-OxoglutarateDehydrogenase Complex The fourth step is performed by a huge complex, composed of three types of 5 enzymes connected by flexible linkers. A lot Succinyl-CoASynthetase of things happen in this complex: another This is the only step in the cycle where ATP is made directly. carbon atom is released as carbon dioxide, The bond between succinate and coenzyme A is particularly electrons are transferred to NADH, and the unstable, and provides the energy needed to build a molecule remaining part of the molecule is connected of ATP. In mitochondria, the enzyme actually creates GTP to coenzyme A. in the reaction, which is converted to ATP by the enzyme nucleoside diphosphate kinase. PDB IDs:1e2o,1bbl,1pmr,2eq7,2jgd PDBID: 2fp4 The structures shown here, taken from several different organisms, are described further in the October 2012 Molecule of the Month (doi:10.2210/rcsb_pdb/mom_2012_10). Visit for more.


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