Citric acid cycle and Oxidative phosphorylation Student

6.8 Pyruvate is oxidized prior to the citric acid cycle This process will not proceed without oxygen The pyruvate formed in glycolysis is transported from the cytoplasm into a mitochondrion where – the citric acid cycle and – oxidative phosphorylation will occur. © 2012 Pearson Education, Inc.

6.8 Pyruvate is oxidized prior to the citric acid cycle Two molecules of pyruvate are produced for each molecule of glucose that enters glycolysis. Pyruvate does not enter the citric acid cycle, but undergoes some chemical grooming in which – a carboxyl group is removed and given off as CO 2, – the two-carbon compound remaining is oxidized while a molecule of NAD + is reduced to NADH, – coenzyme A joins with the two-carbon group to form acetyl coenzyme A, abbreviated as acetyl CoA, and – acetyl CoA enters the citric acid cycle. © 2012 Pearson Education, Inc.

Figure 6.8 Pyruvate Coenzyme A Acetyl coenzyme A NAD  NADHHH CoA CO

6.9 The citric acid cycle The citric acid cycle – is also called the Krebs cycle (after the German- British researcher Hans Krebs, who worked out much of this pathway in the 1930s), – completes the oxidation of organic molecules, and – generates many NADH and FADH 2 molecules. © 2012 Pearson Education, Inc.

Figure 6.9A Acetyl CoA Citric Acid Cycle CoA CO NAD  3 H  NADH ADP ATP P FAD FADH 2

6.9 The citric acid cycle During the citric acid cycle – the two-carbon group of acetyl CoA is added to a four-carbon compound, forming citrate, – citrate is degraded back to the four-carbon compound, – two CO 2 are released, and – 1 ATP, 3 NADH, and 1 FADH 2 are produced. © 2012 Pearson Education, Inc.

6.9 The citric acid cycle Remember that the citric acid cycle processes two molecules of acetyl CoA for each initial glucose. Thus, after two turns of the citric acid cycle, the overall yield per glucose molecule is – 2 ATP, (useable by the cell) – 6 NADH, and – 2 FADH 2. To the electron transport chain © 2012 Pearson Education, Inc.

NOTE Do NOT get overwhelmed by the names of the intermediate compound produced by the citric acid cycle you will NOT be responsible for knowing their names. You may notice: – Each time a carbon(represented by the gray circles) is lost from a carbon compounds a CO2 is produced. – NAD  NADH2 and FAD  FADH2 as the molecules in the citric acid cycle are rearrange and energy is released as high energy electrons.

Figure 6.9B_s3 NADH NAD  NADH HH HH HH CO 2 ATP ADP P FAD FADH 2 CoA Acetyl CoA Oxaloacetate Citric Acid Cycle 2 carbons enter cycle Citrate leaves cycle Alpha-ketoglutarate leaves cycle Succinate Malate Step Acetyl CoA stokes the furnace. Steps – NADH, ATP, and CO 2 are generated during redox reactions. Steps – Further redox reactions generate FADH 2 and more NADH.

6.10 Oxidative phosphorylation At this point in Cellular Respiration only 4 ATP molecules have been produced – 2 in glycolysis – 2 in the citric acid cycle Oxidative phosphorylation (most ATP is produced here) – The energy in NADH2 and FADH2 is converted into ATP – involves electron transport and chemiosmosis and – requires an adequate supply of oxygen. © 2012 Pearson Education, Inc.

6.10 Oxidative phosphorylation (continued) Electrons are released from NADH and FADH 2 and travel down the electron transport chain to O 2. – ETC is a series of proteins embedded in the inner mitochondrial membrane Oxygen “catches” the electrons and picks up H + to form water. © 2012 Pearson Education, Inc.

Oxidative phosphorylation (continued) Energy released by these redox reactions is used to pump H + from the mitochondrial matrix into the intermembrane space. In chemiosmosis, the H + diffuses back across the inner membrane through ATP synthase complexes, driving the synthesis of ATP.

Figure 6.10 Oxidative Phosphorylation Electron Transport Chain Chemiosmosis Mito- chondrial matrix Inner mito- chondrial membrane Intermem- brane space Electron flow Protein complex of electron carriers Mobile electron carriers ATP synthase NADH NAD  2 H  FADH 2 FAD O2O2 H2OH2O ADP PATP 1 2 HH HH HH HH HH HH HH HH HH HH HH I II III IV

6.12 Review: Each molecule of glucose yields many molecules of ATP Recall that the energy payoff of cellular respiration involves 1.glycolysis, 2.alteration of pyruvate, 3.the citric acid cycle, and 4.oxidative phosphorylation. © 2012 Pearson Education, Inc.

6.12 Review: Each molecule of glucose yields many molecules of ATP The total yield is about 32 ATP molecules per glucose molecule. This is about 34% of the potential energy of a glucose molecule. In addition, water and CO 2 are produced. © 2012 Pearson Education, Inc.

Figure 6.12 NADH FADH 2 NADH FADH 2 NADH or NADH Mitochondrion CYTOPLASM Electron shuttles across membrane Glycolysis Glucose 2 Pyruvate Pyruvate Oxidation 2 Acetyl CoA Citric Acid Cycle Oxidative Phosphorylation (electron transport and chemiosmosis) Maximum per glucose: by substrate-level phosphorylation by oxidative phosphorylation ATP  2 about  28 ATP About ATP32ATP  2