Energy Use in Cells Glycolysis, Krebs’s Cycle, Electron Transport, Fermentation & Metabolism

Glycolysis – a single molecule of glucose is enzymatically cut in half through a series of steps, – two molecules of pyruvate are produced, – two molecules of NAD + are reduced to two molecules of NADH, and – a net of two molecules of ATP is produced.

Figure 6.7A Glucose 2 Pyruvate 2 ADP 2 P 2 NAD  2 NADH 2 H  ATP 2

Figure 6.7Ca_s2 Glucose Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate Glyceraldehyde 3-phosphate (G3P) ENERGY INVESTMENT PHASE P P PP P P ADP ATP Step Steps – A fuel molecule is energized, using ATP. Step A six-carbon intermediate splits into two three-carbon intermediates

Figure 6.7Cb_s Step A redox reaction generates NADH. Steps – ATP and pyruvate are produced. ENERGY PAYOFF PHASE 1,3-Bisphospho- glycerate 3-Phospho- glycerate 2-Phospho- glycerate Phosphoenol- pyruvate (PEP) Pyruvate NADH NAD  HH HH ADP ATP H2OH2O H2OH2O P P P P P P P P P P P P P P

The Krebs Cycle Releases Carbon Dioxide and Generates Energy Carriers Pyruvate entering the mitochondrion must be broken down into acetyl CoA before entering the Krebs Cycle Through a series of reactions, the Krebs cycle produces ATP, NADH, and FADH 2, energy carriers that will be used in the final stage of cellular respiration

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

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

The Krebs’s 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, – 6 NADH, and – 2 FADH 2.

Oxidative Phosphorylation Uses Oxygen to Produce ATP in Quantity Oxidative phosphorylation produces the largest amount of ATP during cellular respiration Oxidative phosphorylation is the last stage of cellular respiration and takes place in the many folds (cristae) of the inner mitochondrial membrane

Oxidative Phosphorylation Uses Oxygen to Produce ATP in Quantity Energy carriers produced during the Krebs cycle donate their high-energy electrons to the electron transport chain (ETC), which releases energy as it passes electrons down the chain The energy released from the ETC is used to create a proton gradient

Oxidative Phosphorylation Uses Oxygen to Produce ATP in Quantity The movement of protons through the ATP synthase channel activates enzymes that catalyze the phosphorylation of ADP to from ATP Electrons that travel down the ETC are eventually accepted by O 2 and H + to make water Cellular respiration has a net yield of about 30 to 32 ATP molecules per molecule of glucose

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

Fermentation Facilitates ATP Production Through Glycolysis When Oxygen Is Absent Glycolysis does not require oxygen; it is an anaerobic process During fermentation, the pyruvate and NADH produced by glycolysis remain in the cytosol Postglycolytic reactions convert pyruvate and NADH into other molecules, such as alcohol or lactic acid

Fermentation Facilitates ATP Production Through Glycolysis When Oxygen Is Absent Fermentation by anaerobic yeasts converts pyruvate into an ethanol, releasing CO2 gas Lactic acids forms in severely taxed muscle cells as a result of ATP production in the absence of oxygen

Figure 6.13B 2 NAD  2 NADH 2 NAD  2 NADH 2 Ethanol 2 Pyruvate Glucose 2 ADP 2 ATP 2 P Glycolysis 2 CO 2 p. 101

Figure 6.13A 2 NAD  2 NADH 2 NAD  2 NADH 2 Lactate 2 Pyruvate Glucose 2 ADP 2 ATP 2 P Glycolysis

Figure 6.15_1 Sugars Glycerol Fatty acids Amino acids Amino groups Oxidative Phosphorylation Citric Acid Cycle Pyruvate Oxidation Acetyl CoA Glucose G3P Pyruvate Glycolysis Carbohydrates ATP Fats Proteins Food

Figure 6.16_1 Carbohydrates Fats Proteins Cells, tissues, organisms Amino acids Fatty acids Glycerol Sugars Amino groups Citric Acid Cycle Pyruvate Oxidation Acetyl CoA ATP needed to drive biosynthesis ATP Glucose Synthesis Pyruvate G3PGlucose