Cellular Respiration and Fermentation 7 Cellular Respiration and Fermentation

Concept 7.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis Following glycolysis and the citric acid cycle, NADH and FADH2 account for most of the energy extracted from food These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation © 2016 Pearson Education, Inc. 2

The Pathway of Electron Transport The electron transport chain is located in the inner membrane (cristae) of the mitochondrion Most of the chain’s components are proteins, which exist in multiprotein complexes The carriers alternate reduced and oxidized states as they accept and donate electrons Electrons drop in free energy as they go down the chain and are finally passed to O2, forming H2O © 2016 Pearson Education, Inc. 3

The electron transport chain generates no ATP directly Electrons are transferred from NADH or FADH2 to the electron transport chain Electrons are passed through a number of proteins including cytochromes (each with an iron atom) to O2 The electron transport chain generates no ATP directly It breaks the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts © 2016 Pearson Education, Inc. 4

CITRIC ACID CYCLE OXIDATIVE PHOSPHORYL- ATION PYRUVATE Figure 7.UN09 CITRIC ACID CYCLE OXIDATIVE PHOSPHORYL- ATION PYRUVATE OXIDATION GLYCOLYSIS Figure 7.UN09 In-text figure, mini-map, oxidative phosphorylation, p. 150 ATP © 2016 Pearson Education, Inc.

(least electronegative) Figure 7.12 NADH (least electronegative) 50 2 e- NAD+ FADH2 Free energy (G) relative to O2 (kcal/mol) Complexes I-IV 2 e- FAD 40 I FMN II Fe•S Fe•S Q III Cyt b 30 Fe•S Cyt c1 IV Cyt c Cyt a Electron transport chain Cyt a3 20 Figure 7.12 Free-energy change during electron transport 10 2 e- 2 H+ + ½ O2 (most electronegative) H2O © 2016 Pearson Education, Inc.

(least electronegative) Figure 7.12-1 NADH (least electronegative) 50 2 e- Free energy (G) relative to O2 (kcal/mol) NAD+ FADH2 Complexes I-IV 2 e- FAD I 40 FMN II Fe•S Fe•S Q III Cyt b Fe•S 30 Cyt c1 IV Cyt c Figure 7.12-1 Free-energy change during electron transport (part 1) Cyt a Electron transport chain Cyt a3 20 e- 10 2 © 2016 Pearson Education, Inc.

Free energy (G) relative to O2 (kcal/mol) 30 Figure 7.12-2 Free energy (G) relative to O2 (kcal/mol) Fe•S 30 Cyt c1 IV Cyt c Electron transport chain Cyt a Cyt a3 20 e- 10 2 Figure 7.12-2 Free-energy change during electron transport (part 2) 2 H+ + ½ O2 (most electronegative) H2O © 2016 Pearson Education, Inc.

Chemiosmosis: The Energy-Coupling Mechanism Electron transfer in the electron transport chain causes proteins to pump H from the mitochondrial matrix to the intermembrane space H then moves back across the membrane, passing through the protein complex, ATP synthase ATP synthase uses the exergonic flow of H to drive phosphorylation of ATP This is an example of chemiosmosis, the use of energy in a H gradient to drive cellular work © 2016 Pearson Education, Inc. 9

Video: ATP Synthase 3-D Side View © 2016 Pearson Education, Inc.

Video: ATP Synthase 3-D Top View © 2016 Pearson Education, Inc.

(a) The ATP synthase protein complex Figure 7.13 Intermembrane space Inner mitochondrial membrane Mitochondrial matrix INTERMEMBRANE SPACE H+ Stator Rotor Internal rod Figure 7.13 ATP synthase, a molecular mill Catalytic knob ADP + P ATP i MITOCHONDRIAL MATRIX (a) The ATP synthase protein complex (b) Computer model of ATP synthase © 2016 Pearson Education, Inc.

(a) The ATP synthase protein complex Figure 7.13-1 H+ INTERMEMBRANE SPACE Stator Rotor Internal rod Catalytic knob Figure 7.13-1 ATP synthase, a molecular mill (part 1: ) ADP + MITOCHONDRIAL MATRIX P ATP i (a) The ATP synthase protein complex © 2016 Pearson Education, Inc.

(b) Computer model of ATP synthase Figure 7.13-2 Figure 7.13-2 ATP synthase, a molecular mill (part 2: ) (b) Computer model of ATP synthase © 2016 Pearson Education, Inc.

The energy stored in a H gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis The H gradient is referred to as a proton-motive force, emphasizing its capacity to do work © 2016 Pearson Education, Inc. 15

CITRIC ACID CYCLE OXIDATIVE PHOSPHORYL- ATION PYRUVATE Figure 7.UN09 CITRIC ACID CYCLE OXIDATIVE PHOSPHORYL- ATION PYRUVATE OXIDATION GLYCOLYSIS Figure 7.UN09 In-text figure, mini-map, oxidative phosphorylation, p. 150 ATP © 2016 Pearson Education, Inc.

Electron transport chain Chemiosmosis Figure 7.14 H+ ATP synthase H+ H+ H+ Protein complex of electron carriers Cyt c IV Q III I II 2 H+ + ½ O2 H2O FADH2 FAD NADH NAD+ Figure 7.14 Chemiosmosis couples the electron transport chain to ATP synthesis ADP + P ATP i (carrying electrons from food) H+ Electron transport chain Chemiosmosis Oxidative phosphorylation © 2016 Pearson Education, Inc.

Electron transport chain Figure 7.14-1 H+ H+ H+ Cyt c Protein complex of electron carriers IV Q III I II 2 H+ + ½ O2 H2O FADH2 FAD Figure 7.14-1 Chemiosmosis couples the electron transport chain to ATP synthesis (part 1: electron transport chain) NADH NAD+ (carrying electrons from food) Electron transport chain © 2016 Pearson Education, Inc.

ATP synthase ATP Chemiosmosis H+ ADP + P H+ i Figure 7.14-2 Figure 7.14-2 Chemiosmosis couples the electron transport chain to ATP synthesis (part 2: chemiosmosis) ADP + P ATP i H+ Chemiosmosis © 2016 Pearson Education, Inc.

An Accounting of ATP Production by Cellular Respiration During cellular respiration, most energy flows in the following sequence: glucose  NADH  electron transport chain  proton-motive force  ATP About 34% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 32 ATP There are several reasons why the number of ATP molecules is not known exactly © 2016 Pearson Education, Inc. 20

OXIDATIVE PHOSPHORYLATION CITRIC ACID CYCLE Figure 7.15 CYTOSOL Electron shuttles span membrane MITOCHONDRION 2 NADH or 2 FADH2 2 NADH 2 NADH 6 NADH 2 FADH2 GLYCOLYSIS PYRUVATE OXIDATION OXIDATIVE PHOSPHORYLATION CITRIC ACID CYCLE Glucose 2 Pyruvate 2 Acetyl CoA (Electron transport and chemiosmosis) Figure 7.15 ATP yield per molecule of glucose at each stage of cellular respiration + 2 ATP + 2 ATP + about 26 or 28 ATP About Maximum per glucose: 30 or 32 ATP © 2016 Pearson Education, Inc.

Electron shuttles span membrane GLYCOLYSIS Glucose 2 Pyruvate 2 NADH Figure 7.15-1 Electron shuttles span membrane 2 NADH or 2 FADH2 2 NADH GLYCOLYSIS Glucose 2 Pyruvate Figure 7.15-1 ATP yield per molecule of glucose at each stage of cellular respiration (part 1: glycolysis) + 2 ATP © 2016 Pearson Education, Inc.

PYRUVATE OXIDATION CITRIC ACID CYCLE 2 Acetyl CoA 2 NADH 6 NADH Figure 7.15-2 2 NADH 6 NADH 2 FADH2 PYRUVATE OXIDATION CITRIC ACID CYCLE 2 Acetyl CoA Figure 7.15-2 ATP yield per molecule of glucose at each stage of cellular respiration (part 2: citric acid cycle) + 2 ATP © 2016 Pearson Education, Inc.

OXIDATIVE PHOSPHORYLATION Figure 7.15-3 2 NADH or 2 FADH2 2 NADH 6 NADH 2 FADH2 OXIDATIVE PHOSPHORYLATION (Electron transport and chemiosmosis) Figure 7.15-3 ATP yield per molecule of glucose at each stage of cellular respiration (part 3: oxidative phosphorylation) + about 26 or 28 ATP © 2016 Pearson Education, Inc.

About Maximum per glucose: 30 or 32 ATP Figure 7.15-4 Figure 7.15-4 ATP yield per molecule of glucose at each stage of cellular respiration (part 4: maximum ATP yield per glucose) © 2016 Pearson Education, Inc.

Concept 7.5: Fermentation and anaerobic respiration enable cells to produce ATP without the use of oxygen Most cellular respiration requires O2 to produce ATP Without O2, the electron transport chain will cease to operate In that case, glycolysis couples with fermentation or anaerobic respiration to produce ATP © 2016 Pearson Education, Inc. 26

Anaerobic respiration uses an electron transport chain with a final electron acceptor other than O2, for example, sulfate Fermentation uses substrate-level phosphorylation instead of an electron transport chain to generate ATP © 2016 Pearson Education, Inc. 27

Types of Fermentation Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis Two common types are alcohol fermentation and lactic acid fermentation © 2016 Pearson Education, Inc. 28

In alcohol fermentation, pyruvate is converted to ethanol in two steps The first step releases CO2 from pyruvate, and the second step reduces the resulting acetaldehyde to ethanol Alcohol fermentation by yeast is used in brewing, winemaking, and baking © 2016 Pearson Education, Inc. 29

Animation: Fermentation Overview © 2016 Pearson Education, Inc.

(a) Alcohol fermentation Figure 7.16-1 2 ADP + 2 P 2 ATP i Glucose GLYCOLYSIS 2 Pyruvate 2 NAD+ 2 NADH 2 CO2 + 2 H+ Figure 7.16-1 Fermentation (part 1: alcohol) 2 Ethanol 2 Acetaldehyde (a) Alcohol fermentation © 2016 Pearson Education, Inc.

In lactic acid fermentation, pyruvate is reduced by NADH, forming lactate as an end product, with no release of CO2 Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce © 2016 Pearson Education, Inc. 32

(b) Lactic acid fermentation Figure 7.16-2 2 ADP + 2 P 2 ATP i Glucose GLYCOLYSIS 2 NAD+ 2 NADH + 2 H+ 2 Pyruvate Figure 7.16-2 Fermentation (part 2: lactic acid) 2 Lactate (b) Lactic acid fermentation © 2016 Pearson Education, Inc.

(a) Alcohol fermentation (b) Lactic acid fermentation Figure 7.16 2 ADP + 2 P 2 ATP i 2 ADP + 2 P 2 ATP i Glucose GLYCOLYSIS Glucose GLYCOLYSIS 2 Pyruvate 2 NAD+ 2 NADH 2 CO2 2 NAD+ 2 NADH + 2 H+ + 2 H+ 2 Pyruvate Figure 7.16 Fermentation 2 Ethanol 2 Acetaldehyde 2 Lactate (a) Alcohol fermentation (b) Lactic acid fermentation © 2016 Pearson Education, Inc.

Comparing Fermentation with Anaerobic and Aerobic Respiration All use glycolysis (net ATP = 2) to oxidize glucose and other organic fuels to pyruvate In all three, NAD+ is the oxidizing agent that accepts electrons from food during glycolysis The mechanism of NADH oxidation differs In fermentation the final electron acceptor is an organic molecule such as pyruvate or acetaldehyde Cellular respiration transfers electrons from NADH to a carrier molecule in the electron transport chain © 2016 Pearson Education, Inc. 35

Cellular respiration produces about 32 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule © 2016 Pearson Education, Inc. 36

Obligate anaerobes carry out only fermentation or anaerobic respiration and cannot survive in the presence of O2 Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration In a facultative anaerobe, pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes © 2016 Pearson Education, Inc. 37

Ethanol, lactate, or other products CITRIC ACID CYCLE Figure 7.17 Glucose Glycolysis CYTOSOL Pyruvate No O2 present: Fermentation O2 present: Aerobic cellular respiration MITOCHONDRION Ethanol, lactate, or other products Acetyl CoA Figure 7.17 Pyruvate as a key juncture in catabolism CITRIC ACID CYCLE © 2016 Pearson Education, Inc.

The Evolutionary Significance of Glycolysis Glycolysis is the most common metabolic pathway among organisms on Earth, indicating that it evolved early in the history of life Early prokaryotes may have generated ATP exclusively through glycolysis due to the low oxygen content in the atmosphere The location of glycolysis in the cytosol also indicates its ancient origins; eukaryotic cells with mitochondria evolved much later than prokaryotic cells © 2016 Pearson Education, Inc. 39

Concept 7.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways Glycolysis and the citric acid cycle are major intersections to various catabolic and anabolic pathways © 2016 Pearson Education, Inc. 40

The Versatility of Catabolism Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration Glycolysis accepts a wide range of carbohydrates Proteins must be digested to amino acids and amino groups must be removed before amino acids can feed glycolysis or the citric acid cycle © 2016 Pearson Education, Inc. 41

Fats are digested to glycerol (used in glycolysis) and fatty acids Fatty acids are broken down by beta oxidation and yield acetyl CoA An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate © 2016 Pearson Education, Inc. 42

Proteins Carbohydrates Fats Amino acids Sugars Glycerol acids Figure 7.18-s1 Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids Figure 7.18-s1 The catabolism of various molecules from food (step 1) © 2016 Pearson Education, Inc.

Proteins Carbohydrates Fats Amino acids Sugars Glycerol acids Figure 7.18-s2 Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids GLYCOLYSIS Glucose Glyceraldehyde 3- P NH3 Pyruvate Figure 7.18-s2 The catabolism of various molecules from food (step 2) © 2016 Pearson Education, Inc.

Proteins Carbohydrates Fats Amino acids Sugars Glycerol acids Figure 7.18-s3 Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids GLYCOLYSIS Glucose Glyceraldehyde 3- P NH3 Pyruvate Figure 7.18-s3 The catabolism of various molecules from food (step 3) Acetyl CoA © 2016 Pearson Education, Inc.

Amino acids CITRIC ACID CYCLE Figure 7.18-s4 Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids GLYCOLYSIS Glucose Glyceraldehyde 3- P NH3 Pyruvate Figure 7.18-s4 The catabolism of various molecules from food (step 4) Acetyl CoA CITRIC ACID CYCLE © 2016 Pearson Education, Inc.

Amino acids CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION Figure 7.18-s5 Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids GLYCOLYSIS Glucose Glyceraldehyde 3- P NH3 Pyruvate Figure 7.18-s5 The catabolism of various molecules from food (step 5) Acetyl CoA CITRIC ACID CYCLE OXIDATIVE PHOSPHORYLATION © 2016 Pearson Education, Inc.

Biosynthesis (Anabolic Pathways) The body uses small molecules to build other substances Some of these small molecules come directly from food; others can be produced during glycolysis or the citric acid cycle © 2016 Pearson Education, Inc. 48

Figure 7.UN10-1 Figure 7.UN10-1 Skills exercise: making a bar graph and evaluating a hypothesis (part 1) © 2016 Pearson Education, Inc.

Figure 7.UN10-2 Figure 7.UN10-2 Skills exercise: making a bar graph and evaluating a hypothesis (part 2) © 2016 Pearson Education, Inc.

ATP NADH Inputs Outputs GLYCOLYSIS Glucose 2 Pyruvate 2 2 Figure 7.UN11 Inputs Outputs GLYCOLYSIS Glucose 2 Pyruvate 2 ATP 2 NADH Figure 7.UN11 Summary of key concepts: glycolysis © 2016 Pearson Education, Inc.

CO2 F A DH2 Inputs Outputs 2 Pyruvate 2 Acetyl CoA 2 ATP 8 NADH CITRIC Figure 7.UN12 Inputs Outputs 2 Pyruvate 2 Acetyl CoA 2 ATP 8 NADH CITRIC ACID CYCLE 2 Oxaloacetate 6 CO2 2 F A DH2 Figure 7.UN12 Summary of key concepts: citric acid cycle © 2016 Pearson Education, Inc.

Cyt c IV Q III I II INTERMEMBRANE SPACE H+ H+ H+ Protein complex Figure 7.UN13 INTERMEMBRANE SPACE H+ H+ H+ Cyt c Protein complex of electron carriers IV Q III I Figure 7.UN13 Summary of key concepts: electron transport chain II 2 H+ O2 + ½ H2O FA DH2 FAD NA DH NAD+ MITOCHONDRIAL MATRIX (carrying electrons from food) © 2016 Pearson Education, Inc.

ATP INTER- MEMBRANE SPACE H+ ATP synthase ADP + P H+ MITO CHONDRIAL Figure 7.UN14 INTER- MEMBRANE SPACE H+ MITO CHONDRIAL MATRIX ATP synthase Figure 7.UN14 Summary of key concepts: chemiosmosis ADP + P H+ ATP i © 2016 Pearson Education, Inc.

across membrane pH difference Figure 7.UN15 across membrane pH difference Figure 7.UN15 Test your understanding, question 8 (pH vs. time) Time © 2016 Pearson Education, Inc.

Phosphofructokinase activity Fructose 6-phosphate concentration Figure 7.UN16 Low ATP concentration Phosphofructokinase activity High ATP concentration Figure 7.UN16 Test your understanding, question 9 (regulation of phosphofructokinase) Fructose 6-phosphate concentration © 2016 Pearson Education, Inc.

Figure 7.UN17 Test your understanding, question 13 (Coenzyme Q) © 2016 Pearson Education, Inc.