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Warm Up

Warm Up. Does glycolysis require a specialized organelle. What are the outputs of glycolysis? How many carbons does pyruvate have? Only 2 ATP are produced from glucose during glycolysis. Where is the rest of the energy stockpiled?. Figure 6.3. ELECTRON TRANSPORT AND

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Warm Up

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  1. Warm Up • Does glycolysis require a specialized organelle. • What are the outputs of glycolysis? • How many carbons does pyruvate have? • Only 2 ATP are produced from glucose during glycolysis. Where is the rest of the energy stockpiled?

  2. Figure 6.3 ELECTRON TRANSPORT AND OXIDATIVE PHOSPHORYLATION GLYCOLYSIS KREBS CYCLE NADH NADH NADH FADH2 Electron transport chain... Krebs Cycle CO2 Pyruvate Glucose H2O CO2 ATP ATP ATP Electron transport chain establishes proton gradient. Oxidative phosphorylation uses proton gradient to produce ATP.

  3. Glucose CYTOSOL Pyruvate No O2 present Fermentation O2 present Cellular respiration MITOCHONDRION Ethanol or lactate Acetyl CoA Citric acid cycle Figure 9.18 Pyruvate is a key juncture in catabolism.

  4. Under Aerobic Conditions • Pyruvate made during glycolysis is absorbed by the mitochondrion. • It travels to the mitochondrial matrix. • Aerobic: These reactions can occur only if oxygen is present.

  5. Forming Acetyl CoA: • Enzymes in the mitochondrial matrix remove electrons and CO2 from pyruvate. • This results in the formation of an acetyl group (CH3CO), which is accepted by coenzyme A. • This combination is called Acetyl CoA.

  6. What is a coenzyme? • A coenzyme is an organic, non-protein molecule that is required for the proper functioning of an enzyme. • Coenzyme A is derived from vitamin B.

  7. What Happened? • The process of converting Pyruvate to Acetyl CoA is called Oxidative Decarboxylation. • Pyruvate is oxidized (NAD+ is reduced to NADH). • Removal of carbon dioxide is the decarboxylation.

  8. Initiating the cycle • Coenzyme A transfers the Acetyl group to a four-carbon molecule called oxaloacetate. • This forms a six-carbon molecule called citrate. • Citrate is converted back into oxaloacetate over the course of the cycle.

  9. Three types of reactions • Decarboxylations: These produce CO2, a waste product that must be excreted. • Oxidations: These release energy, much of which is stored by the carriers when they accept hydrogen (e.g. NADH). • Substrate-level phosphorylation: ATP is produced in one of the reactions as a substrate transfers a phosphate to ADP.

  10. Key Points • For each acetyl group that enters the cycle: • 2 carbons enter in the reduced form of the acetyl group, and 2 different carbons leave as fully oxidized CO2 molecules. • One ATP molecule is produced. • 3 NAD+ are reduced to NADH and 1 FAD is reduced to FADH2. • Most of the energy is transferred to NAD+ and FAD during the redox reactions.

  11. The Power of NADH • As electrons shift toward a more electronegative atom, they give up potential energy. • Thus, chemical energy is released as NADH is converted to NAD+. • The reduced coenzymes, NADH and FADH2, shuttle their high-energy electrons to the electron transport chain.

  12. What happens to pyruvate? • Each pyruvate is broken down to three CO2 molecules. • One of these is produced during the conversion from pyruvate to the acetyl group. • The other two are produced in the cycle. • The cycle generates 1 ATP per turn. • Most of the energy is transferred to NAD+ and FAD during the redox reactions. • One NADH is produced during the conversion from pyruvate to the acetyl group. • Three NADH and one FADH2 are formed in the citric acid cycle.

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