bio chapter 9 - Chapter 9: Cellular Respiration Lecture 15:...

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Chapter 9: Cellular Respiration Lecture 15: Bioenergetics II 9.3 T HE C ITRIC A CID C YCLE C OMPLETES THE E NERGY -Y IELDING O XIDATION OF O RGANIC M OLECULES -if oxygen is present, the pyruvate enters a mitochondrion (in eukaryotic cells) where enzymes of citric acid cycle complete the oxidation of glucose (in prokaryotic cells: cytosol) -upon entering mitochondrion pyruvate converted into acetyl coenzyme A or acetyl CoA : by multienzyme complex that catalyzes three reactions 1- pyruvate’s carboxyl group which is already fully oxidized and has little chemical energy is removed and given off as a CO2 2- remaining 2 carbon fragment is oxidized forming a compound, acetate. An enzyme transfers the extracted electrons to NAD+, storing energy in the form of NADH 3- coenzyme A attached to the acetate by an unstable bond that makes the acetyl group very reactive (high potential energy) -citric acid cycle also called tricarboxylic acid cycle or the krebs cycle -metabolic furnace that oxidizes organic fuel derived from pyruvate -pyruvate is broken down to 3 CO2 molecules (including when it was released from pyruvate) -generates 1 ATP per turn by substrate level phosphorylation but most of the chemical energy is transferred to NAD+ and a related electron carrier, the coenzyme FAD …reduced coenzymes, NADH and FADH2 -reduced NADH and FADH2 transport e- to ETC -for each turn of citric acid cycle, 2 carbons enter in the reduced form of an acetyl group (step 1) and two different carbons leave in the completely oxidized form of CO2, molecules (step 3 and 4) -for each cycle of the citric acid cycle, 3 NAD+ are reduced to NADH (steps 3, 4, and 8) -step 6: electrons are transferred to FAD which accepts 2 electrons and 2 protons to become FADH2 -animal cells: step 5 produces a guanosine triphosphate (GTP) molecule by substrate-level phoshorylataion -GTP similar to ATP in structure and cellular function -may be used to make an ATP molecule or directly power work in the cell -step 5 forms an ATP molecule directly by substrate level phosphorylation…represents only ATP generated directly by the citric acid cycle -most of the ATP produced by respiration results from oxidative -A Closer Look to the Citric Acid Cycle phosphorylation, when the NADH and FADH2, produced by the citric acid cycle relay the e- extracted from food to the ETC 1) Acetyl CoA adds its 2 carbon acetyl group to oxaloacetate, producing citrate 2) Citrate is converted to its isomer , isocitrate , by removal of one water molecule and addition of another 3) Isocitrate is oxidized reducing NAD+ to NADH 4) Another CO2 is lost , and the resulting compound is oxidized , reducing NAD+ to NADH. The remaining molecule is then attached to coenzyme A by an unstable bond. 5)
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This note was uploaded on 03/03/2010 for the course BIOG 1101 taught by Professor N/a during the Fall '10 term at Cornell University (Engineering School).

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bio chapter 9 - Chapter 9: Cellular Respiration Lecture 15:...

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