Cellular Respiration and Fermentation

Cellular Respiration and Fermentation
7 Cellular Respiration and Fermentation

Life Is Work Living cells require energy from outside sources
Some animals, such as the giraffe, obtain energy by eating plants, and some animals feed on other organisms that eat plants © 2016 Pearson Education, Inc. 2

Energy flows into an ecosystem as sunlight and leaves as heat
Photosynthesis generates O2 and organic molecules, which are used as fuel for cellular respiration Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work © 2016 Pearson Education, Inc. 3

Light energy ECOSYSTEM Photosynthesis in chloroplasts Organic
Figure 7.2 Light energy ECOSYSTEM Photosynthesis in chloroplasts Organic molecules CO2 + H2O + O2 Cellular respiration in mitochondria Figure 7.2 Energy flow and chemical recycling in ecosystems ATP powers most cellular work ATP Heat energy © 2016 Pearson Education, Inc.

Concept 7.1: Catabolic pathways yield energy by oxidizing organic fuels
Catabolic pathways involving electron transfer are central processes to cellular respiration © 2016 Pearson Education, Inc. 5

Catabolic Pathways and Production of ATP
The breakdown of organic molecules is exergonic Fermentation is a partial degradation of sugars that occurs without O2 Aerobic respiration consumes organic molecules and O2 and yields ATP Anaerobic respiration is similar to aerobic respiration but consumes compounds other than O2 © 2016 Pearson Education, Inc. 6

C6H12O6  6 O2  6 CO2  6 H2O  Energy (ATP  heat)
Cellular respiration includes both aerobic and anaerobic processes but is often used to refer to aerobic respiration Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose C6H12O6  6 O2  6 CO2  6 H2O  Energy (ATP  heat) © 2016 Pearson Education, Inc. 7

Redox Reactions: Oxidation and Reduction
The transfer of electrons during chemical reactions releases energy stored in organic molecules This released energy is ultimately used to synthesize ATP © 2016 Pearson Education, Inc. 8

The Principle of Redox Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions In oxidation, a substance loses electrons, or is oxidized In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced) © 2016 Pearson Education, Inc. 9

becomes oxidized becomes reduced Figure 7.UN02
Figure 7.UN02 In-text figure, generalized redox reaction, p. 142 © 2016 Pearson Education, Inc.

The electron donor is called the reducing agent
The electron acceptor is called the oxidizing agent Some redox reactions do not transfer electrons but change the electron sharing in covalent bonds An example is the reaction between methane and O2 © 2016 Pearson Education, Inc. 11

Reactants Products Methane Oxygen Carbon dioxide Water
Figure 7.3 Reactants Products becomes oxidized becomes reduced Figure 7.3 Methane combustion as an energy-yielding redox reaction Methane Oxygen Carbon dioxide Water (reducing agent) (oxidizing agent) © 2016 Pearson Education, Inc.

Oxidation of Organic Fuel Molecules During Cellular Respiration
During cellular respiration, fuel (such as glucose) is oxidized, and O2 is reduced Organic molecules with an abundance of hydrogen, like carbohydrates and fats, are excellent fuels As hydrogen (with its electron) is transferred to oxygen, energy is released that can be used in ATP synthesis © 2016 Pearson Education, Inc. 14

becomes oxidized becomes reduced Figure 7.UN03
Figure 7.UN03 In-text figure, cellular respiration redox reaction, p. 143 © 2016 Pearson Education, Inc.

Stepwise Energy Harvest via NAD+ and the Electron Transport Chain
In cellular respiration, glucose and other organic molecules are broken down in a series of steps Electrons from organic compounds are usually first transferred to NAD+, a coenzyme As an electron acceptor, NAD+ functions as an oxidizing agent during cellular respiration Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP © 2016 Pearson Education, Inc. 16

One hydrogen ion is released in this process
Enzymes called dehydrogenases facilitate the transfer of two electrons and one hydrogen ion to NAD+ One hydrogen ion is released in this process © 2016 Pearson Education, Inc. 17

2 e + 2 H+ 2 e + H+ NAD+ H+ NADH Dehydrogenase Reduction of NAD+
Figure 7.4 2 e + 2 H+ 2 e + H+ NAD+ NADH H+ Dehydrogenase Reduction of NAD+ 2[H] H+ (from food) Oxidation of NADH Nicotinamide Nicotinamide (oxidized form) (reduced form) Figure 7.4 NAD+ as an electron shuttle © 2016 Pearson Education, Inc.

NADH passes the electrons to the electron transport chain
Electrons are passed to increasingly electronegative carrier molecules down the chain through a series of redox reactions Electron transfer to oxygen occurs in a series of energy-releasing steps instead of one explosive reaction The energy yielded is used to regenerate ATP © 2016 Pearson Education, Inc. 19

Controlled release of energy release
Figure 7.5 H2 + 1/2 O2 2 H + 1 /2 O2 Controlled release of energy 2 H+ + 2 e ATP Free energy, G Free energy, G ATP Explosive release chain Electron transport ATP 2 e  Figure 7.5 An introduction to electron transport chains 1/2 O2 2 H+ H2O H2O (a) Uncontrolled reaction (b) Cellular respiration © 2016 Pearson Education, Inc.

The Stages of Cellular Respiration: A Preview
Harvesting of energy from glucose has three stages Glycolysis breaks down glucose into two molecules of pyruvate in the cytosol Pyruvate oxidation and the citric acid cycle completes the breakdown of glucose in the mitochondrial matrix Oxidative phosphorylation accounts for most of the ATP synthesis and occurs in the inner membrane of the mitochondria © 2016 Pearson Education, Inc. 21

1. GLYCOLYSIS (color-coded blue throughout the chapter)
Figure 7.UN05 1. GLYCOLYSIS (color-coded blue throughout the chapter) 2. PYRUVATE OXIDATION and the CITRIC ACID CYCLE (color-coded orange) 3. OXIDATIVE PHOSPHORYLATION: Electron transport and chemiosmosis (color-coded purple) Figure 7.UN05 In-text figure, color code for stages of cellular respiration, p. 145 © 2016 Pearson Education, Inc.

Electrons via NADH GLYCOLYSIS Glucose Pyruvate CYTOSOL MITOCHONDRION
Figure 7.6-s1 Electrons via NADH GLYCOLYSIS Glucose Pyruvate CYTOSOL MITOCHONDRION Figure 7.6-s1 An overview of cellular respiration (step 1) ATP Substrate-level © 2016 Pearson Education, Inc.

and FADH2 CITRIC ACID CYCLE
Figure 7.6-s2 Electrons via NADH Electrons via NADH and FADH2 GLYCOLYSIS PYRUVATE OXIDATION CITRIC ACID CYCLE Glucose Pyruvate Acetyl CoA CYTOSOL MITOCHONDRION Figure 7.6-s2 An overview of cellular respiration (step 2) ATP ATP Substrate-level Substrate-level © 2016 Pearson Education, Inc.

Electrons via NADH Electrons via NADH and FADH2 GLYCOLYSIS PYRUVATE
Figure 7.6-s3 Electrons via NADH Electrons via NADH and FADH2 GLYCOLYSIS PYRUVATE OXIDATION OXIDATIVE PHOSPHORYLATION CITRIC ACID CYCLE Glucose Pyruvate Acetyl CoA (Electron transport and chemiosmosis) CYTOSOL MITOCHONDRION Figure 7.6-s3 An overview of cellular respiration (step 3) ATP ATP ATP Substrate-level Substrate-level Oxidative © 2016 Pearson Education, Inc.

This process involves the transfer of inorganic phosphates to ADP
Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration This process involves the transfer of inorganic phosphates to ADP © 2016 Pearson Education, Inc. 26

A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation In this process, an enzyme transfers a phosphate group directly from a substrate molecule to ADP © 2016 Pearson Education, Inc. 27

Enzyme Enzyme ADP P Substrate ATP Product Figure 7.7
Figure 7.7 Substrate-level phosphorylation Product © 2016 Pearson Education, Inc.

Concept 7.2: Glycolysis harvests chemical energy by oxidizing glucose to pyruvate
Glycolysis (“sugar splitting”) breaks down glucose into two molecules of pyruvate Glycolysis occurs in the cytoplasm and has two major phases Energy investment phase Energy payoff phase The net energy yield is 2 ATP plus 2 NADH per glucose molecule Glycolysis occurs whether or not O2 is present © 2016 Pearson Education, Inc. 30

CITRIC ACID CYCLE OXIDATIVE PHOSPHORYL- ATION PYRUVATE
Figure 7.UN06 CITRIC ACID CYCLE OXIDATIVE PHOSPHORYL- ATION PYRUVATE OXIDATION GLYCOLYSIS Figure 7.UN06 In-text figure, mini-map, glycolysis, p. 147 ATP © 2016 Pearson Education, Inc.

Energy Investment Phase
Figure 7.8 Energy Investment Phase Glucose 2 ATP used 2 ADP + 2 P Energy Payoff Phase 4 ADP P 4 ATP formed 2 NAD e + 4 H+ 2 NADH + 2 H+ Figure 7.8 The energy input and output of glycolysis 2 Pyruvate + 2 H2O Net Glucose 2 Pyruvate + 2 H2O 4 ATP formed - 2 ATP used 2 ATP 2 NAD e + 4 H+ 2 NADH + 2 H+ © 2016 Pearson Education, Inc.

GLYCOLYSIS: Energy Investment Phase
Figure 7.9-1 GLYCOLYSIS: Energy Investment Phase Glyceraldehyde 3-phosphate (G3P) ATP Glucose 6-phosphate Fructose 6-phosphate ATP Fructose 1,6-bisphosphate Glucose ADP ADP Isomerase Hexokinase Phosphogluco- isomerase Phospho- fructokinase Aldolase Dihydroxyacetone phosphate (DHAP) Figure A closer look at glycolysis (part 1: investment phase) © 2016 Pearson Education, Inc.

Figure 7.9-1a-s3 GLYCOLYSIS: Energy Investment Phase ATP Glucose 6-phosphate Fructose 6-phosphate Glucose ADP Hexokinase Phosphogluco- isomerase Figure 7.9-1a-s3 A closer look at glycolysis (part 1a, step 3) © 2016 Pearson Education, Inc.

Figure 7.9-1b-s2 GLYCOLYSIS: Energy Investment Phase Fructose 6-phosphate Fructose 1,6-bisphosphate ATP ADP Phospho- fructokinase Figure 7.9-1b-s2 A closer look at glycolysis (part 1b, step 2) © 2016 Pearson Education, Inc.

Figure 7.9-1b-s3 GLYCOLYSIS: Energy Investment Phase Glyceraldehyde 3-phosphate (G3P) Fructose 6-phosphate Fructose 1,6-bisphosphate ATP ADP Isomerase Phospho- fructokinase Aldolase Dihydroxyacetone phosphate (DHAP) Figure 7.9-1b-s3 A closer look at glycolysis (part 1b, step 3) © 2016 Pearson Education, Inc.

GLYCOLYSIS: Energy Payoff Phase
Figure 7.9-2 GLYCOLYSIS: Energy Payoff Phase 2 ATP 2 ATP 2 NADH 2 H2O Glyceraldehyde 3-phosphate (G3P) 2 ADP 2 NA D+ + 2 H+ 2 ADP 2 2 2 2 2 Triose phosphate dehydrogenase Phospho- glycerokinase Phospho- glyceromutase Enolase Pyruvate kinase 2 P i 1,3-Bisphospho- glycerate 3-Phospho- glycerate 2-Phospho- glycerate Phosphoenol- pyruvate (PEP) Pyruvate Figure A closer look at glycolysis (part 2: payoff phase) © 2016 Pearson Education, Inc.

Figure 7.9-2a-s1 GLYCOLYSIS: Energy Payoff Phase Glyceraldehyde 3-phosphate (G3P) Isomerase Aldolase Dihydroxyacetone phosphate (DHAP) Figure 7.9-2a-s1 A closer look at glycolysis (part 2a, step 1) © 2016 Pearson Education, Inc.

Figure 7.9-2a-s2 GLYCOLYSIS: Energy Payoff Phase 2 NADH Glyceraldehyde 3-phosphate (G3P) 2 NAD+ + 2 H+ 2 Triose phosphate dehydrogenase 2 P i Isomerase 1,3-Bisphospho- glycerate Aldolase Dihydroxyacetone phosphate (DHAP) Figure 7.9-2a-s2 A closer look at glycolysis (part 2a, step 2) © 2016 Pearson Education, Inc.

Figure 7.9-2a-s3 GLYCOLYSIS: Energy Payoff Phase 2 ATP 2 NADH Glyceraldehyde 3-phosphate (G3P) 2 NAD+ + 2 H+ 2 ADP 2 2 Triose phosphate dehydrogenase Phospho- glycerokinase 2 P i Isomerase 1,3-Bisphospho- glycerate 3-Phospho- glycerate Aldolase Dihydroxyacetone phosphate (DHAP) Figure 7.9-2a-s3 A closer look at glycolysis (part 2a, step 3) © 2016 Pearson Education, Inc.

Figure 7.9-2b-s2 GLYCOLYSIS: Energy Payoff Phase 2 H2O 2 2 2 Phospho- glyceromutase Enolase Figure 7.9-2b-s2 A closer look at glycolysis (part 2b, step 2) 3-Phospho- glycerate 2-Phospho- glycerate Phosphoenol- pyruvate (PEP) © 2016 Pearson Education, Inc.

Figure 7.9-2b-s3 GLYCOLYSIS: Energy Payoff Phase 2 ATP 2 H2O 2 ADP 2 2 2 2 Phospho- glyceromutase Enolase Pyruvate kinase Figure 7.9-2b-s3 A closer look at glycolysis (part 2b, step 3) 3-Phospho- glycerate 2-Phospho- glycerate Phosphoenol- pyruvate (PEP) Pyruvate © 2016 Pearson Education, Inc.

Concept 7.3: After pyruvate is oxidized, the citric acid cycle completes the energy-yielding oxidation of organic molecules In the presence of O2, pyruvate enters the mitochondrion (in eukaryotic cells), where the oxidation of glucose is completed Before the citric acid cycle can begin, pyruvate must be converted to acetyl coenzyme A (acetyl CoA), which links glycolysis to the citric acid cycle © 2016 Pearson Education, Inc. 47

2 molecules per glucose) CYTOSOL
Figure 7.10 Pyruvate (from glycolysis, 2 molecules per glucose) CYTOSOL PYRUVATE OXIDATION CO2 NAD+ CoA NADH + H+ Acetyl CoA CoA CoA Figure 7.10 An overview of pyruvate oxidation and the citric acid cycle CITRIC ACID CYCLE 2 CO2 FADH2 3 NAD+ 3 NADH FAD + 3 H+ ADP + P i ATP MITOCHONDRION © 2016 Pearson Education, Inc.

2 molecules per glucose) CYTOSOL
Figure Pyruvate (from glycolysis, 2 molecules per glucose) CYTOSOL PYRUVATE OXIDATION CO2 NAD+ Figure An overview of pyruvate oxidation and the citric acid cycle (part 1: pyruvate oxidation) CoA NADH + H+ Acetyl CoA CoA MITOCHONDRION © 2016 Pearson Education, Inc.

Acetyl CoA CoA CoA CITRIC ACID CYCLE 2 CO2 3 NAD+ FADH2 3 NADH FAD
Figure Acetyl CoA CoA CoA CITRIC ACID CYCLE 2 CO2 FADH2 3 NAD+ Figure An overview of pyruvate oxidation and the citric acid cycle (part 2: citric acid cycle) 3 NADH FAD + 3 H+ ADP + P i ATP MITOCHONDRION © 2016 Pearson Education, Inc.

The citric acid cycle, also called the Krebs cycle, completes the breakdown of pyruvate to CO2
The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn © 2016 Pearson Education, Inc. 52

The citric acid cycle has eight steps, each catalyzed by a specific enzyme
The acetyl group of acetyl CoA joins the cycle by combining with oxaloacetate, forming citrate The next seven steps decompose the citrate back to oxaloacetate, making the process a cycle The NADH and FADH2 produced by the cycle relay electrons extracted from food to the electron transport chain © 2016 Pearson Education, Inc. 53

CITRIC ACID CYCLE Figure 7.11-s1 Acetyl CoA Oxaloacetate Citrate
CoA-SH H2O Oxaloacetate Citrate Isocitrate CITRIC ACID CYCLE Figure 7.11-s1 A closer look at the citric acid cycle (step 1) © 2016 Pearson Education, Inc.

CoA-SH H2O Oxaloacetate Citrate Isocitrate CITRIC ACID CYCLE NAD+ NADH + H+ CO2 CoA-SH a-Ketoglutarate Figure 7.11-s3 A closer look at the citric acid cycle (step 3) CO2 NAD+ NADH + H+ Succinyl CoA © 2016 Pearson Education, Inc.

CoA-SH H2O Oxaloacetate Citrate Isocitrate CITRIC ACID CYCLE NAD+ NADH + H+ CO2 CoA-SH a-Ketoglutarate Figure 7.11-s4 A closer look at the citric acid cycle (step 4) CoA-SH CO2 NAD+ NADH Succinate P i + H+ GTP GDP Succinyl CoA ADP ATP © 2016 Pearson Education, Inc.

CoA-SH H2O Oxaloacetate Citrate Isocitrate CITRIC ACID CYCLE NAD+ NADH + H+ CO2 Fumarate CoA-SH a-Ketoglutarate Figure 7.11-s5 A closer look at the citric acid cycle (step 5) CoA-SH FADH2 CO2 NAD+ FAD NADH Succinate P i + H+ GTP GDP Succinyl CoA ADP ATP © 2016 Pearson Education, Inc.

CITRIC ACID CYCLE Figure 7.11-s6 Acetyl CoA Oxaloacetate Malate
CoA-SH NADH + H+ H2O NAD+ Oxaloacetate Malate Citrate Isocitrate CITRIC ACID CYCLE NAD+ NADH + H+ H2O CO2 Fumarate CoA-SH a-Ketoglutarate Figure 7.11-s6 A closer look at the citric acid cycle (step 6) CoA-SH FADH2 CO2 NAD+ FAD NADH Succinate P i + H+ GTP GDP Succinyl CoA ADP ATP © 2016 Pearson Education, Inc.

Start: Acetyl CoA adds its two-carbon group to oxaloacetate, producing
Figure Start: Acetyl CoA adds its two-carbon group to oxaloacetate, producing citrate; this is a highly exergonic reaction. Acetyl CoA CoA-SH H2O Figure A closer look at the citric acid cycle (part 1) Oxaloacetate Citrate Isocitrate © 2016 Pearson Education, Inc.

Isocitrate is oxidized; NAD+ is reduced.
Figure Isocitrate Redox reaction: Isocitrate is oxidized; NAD+ is reduced. NAD+ NADH + H+ CO2 CO2 release CoA-SH a-Ketoglutarate Figure A closer look at the citric acid cycle (part 2) CO2 CO2 release NAD+ Redox reaction: NADH After CO2 release, the resulting four-carbon molecule is oxidized (reducing NAD+), then made reactive by addition of CoA. + H+ Succinyl CoA © 2016 Pearson Education, Inc.

Succinate is oxidized; FAD is reduced.
Figure Fumarate CoA-SH FADH2 FAD Redox reaction: Succinate is oxidized; FAD is reduced. Succinate P i GTP GDP Succinyl Figure A closer look at the citric acid cycle (part 3) CoA ADP ATP formation ATP © 2016 Pearson Education, Inc.

Redox reaction: Malate is oxidized; NAD+ is reduced. Oxaloacetate
Figure Redox reaction: Malate is oxidized; NAD+ is reduced. NADH + H+ NAD+ Oxaloacetate Malate Figure A closer look at the citric acid cycle (part 4) H2O Fumarate © 2016 Pearson Education, Inc.

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. 65

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. 66

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. 67

(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 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 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 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 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. 72

(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 H+ INTERMEMBRANE SPACE Stator Rotor Internal rod Catalytic knob Figure ATP synthase, a molecular mill (part 1: ) ADP + MITOCHONDRIAL MATRIX P ATP i (a) The ATP synthase protein complex © 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. 75

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 H+ H+ H+ Cyt c Protein complex of electron carriers IV Q III I II 2 H+ + ½ O2 H2O FADH2 FAD Figure 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 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. 80

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 Electron shuttles span membrane 2 NADH or 2 FADH2 2 NADH GLYCOLYSIS Glucose 2 Pyruvate Figure 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 2 NADH 6 NADH 2 FADH2 PYRUVATE OXIDATION CITRIC ACID CYCLE 2 Acetyl CoA Figure 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 2 NADH or 2 FADH2 2 NADH 6 NADH 2 FADH2 OXIDATIVE PHOSPHORYLATION (Electron transport and chemiosmosis) Figure 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 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. 86

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. 87

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. 88

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. 89

(a) Alcohol fermentation
Figure 2 ADP + 2 P 2 ATP i Glucose GLYCOLYSIS 2 Pyruvate 2 NAD+ 2 NADH 2 CO2 + 2 H+ Figure 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. 91

(b) Lactic acid fermentation
Figure 2 ADP + 2 P 2 ATP i Glucose GLYCOLYSIS 2 NAD+ 2 NADH + 2 H+ 2 Pyruvate Figure 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. 94

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. 96

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. 98

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. 99

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. 100

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. 101

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.

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.

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. 107

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.

Cellular Respiration and Fermentation

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Cellular Respiration and Fermentation

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