Cellular Respiration: Harvesting Chemical Energy

Cellular Respiration: Harvesting Chemical Energy
Chapter 9 Cellular Respiration: Harvesting Chemical Energy

Living cells require energy from outside sources
Overview: Life Is Work Living cells require energy from outside sources Some animals, such as the giant panda, obtain energy by eating plants, and some animals feed on other organisms that eat plants For the Discovery Video Space Plants, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Energy flows into an ecosystem as sunlight and leaves as heat
Photosynthesis generates O2 and organic molecules, which are used in cellular respiration Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

+ H2O Energy for cellular work (endergonic, energy-consuming
Fig. 8-12 ATP + H2O Energy from catabolism (exergonic, energy-releasing processes) Energy for cellular work (endergonic, energy-consuming processes) WHAT metabolic process is shown to the left? To the right? ADP + P i

Organic molecules Cellular respiration in mitochondria
Fig. 9-2 Light energy ECOSYSTEM Photosynthesis in chloroplasts Organic molecules CO2 + H2O + O2 Cellular respiration in mitochondria Figure 9.2 Energy flow and chemical recycling in ecosystems ATP ATP powers most cellular work Heat energy

Concept 9.1: Catabolic pathways yield energy by oxidizing organic fuels
Several processes are central to cellular respiration and related pathways Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy (ATP + heat)
Cellular respiration includes both aerobic and anaerobic respiration 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) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

In oxidation, a substance loses electrons, or is oxidized
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) Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

becomes oxidized (loses electron) becomes reduced (gains electron)
Fig. 9-UN1 becomes oxidized (loses electron) becomes reduced (gains electron)

becomes oxidized becomes reduced
Fig. 9-UN2 becomes oxidized becomes reduced

The electron donor is called the reducing agent
The electron receptor 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Methane (reducing agent) Oxygen (oxidizing agent)
Fig. 9-3 Reactants Products becomes oxidized becomes reduced When Methane (the fuel!) reacts with Oxygen, the electrons move away from the Carbon, oxidizing it to CO2 in the presence of Oxygen, and electrons move towards the Oxygen, reducing it to Water in the presence of Hydrogen. The products lose potential energy when their electrons end up being shared unequally. WHY? The electrons are more stable. It takes more energy to break a polar molecule of its electrons than a nonpolar one. Energy is released in this very catabolic combustion reaction. Methane (reducing agent) Oxygen (oxidizing agent) Carbon dioxide Water

Oxidation of Organic Fuel Molecules During Cellular Respiration
During cellular respiration, the fuel is glucose, and is oxidized to CO2, while O2 is reduced to water. This occurs in multiple steps. Energy in the form of, not heat, but ______is the result! Why GLUCOSE? It has lots of yummy, easily accessible electrons in its Hydrogens. In Cellular Respiration, electrons are often removed from organics with their protons. In other words, a ___________ atom is removed. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

So, why do we breathe? What molecule does all the REDOXing?
Fig. 9-UN3 So, why do we breathe? becomes oxidized becomes reduced What molecule does all the REDOXing?

Fig. 9-UN4 Dehydrogenase

Stepwise Energy Harvest via NAD+ and the Electron Transport Chain
Electrons and protons from organic compounds are usually first transferred to NAD+, which is a coenzyme Each NADH (the reduced form of NAD+) represents stored energy that is later tapped to synthesize ATP Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

NADH H+ NAD+ + 2[H] + H+ 2 e– + 2 H+ 2 e– + H+ Dehydrogenase
Fig. 9-4 2 e– + 2 H+ 2 e– + H+ NADH H+ Dehydrogenase Reduction of NAD+ NAD+ + 2[H] + H+ Oxidation of NADH Nicotinamide (reduced form) Nicotinamide (oxidized form) Figure 9.4 NAD+ as an electron shuttle. LOOK FAMILIAR???

NADHs purpose is to pass the electrons to a place where the are transported down a chain. This is called the _______ _______ _______ Here, O2 pulls electrons down the chain in an massive energy-yielding tumble! This energy makes water, but MORE importantly, it is used to generate lots of ATP!! Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

(a) Uncontrolled reaction (b) Cellular respiration
Fig. 9-5 H2 + 1/2 O2 2 H + 1/2 O2 (from food via NADH) Controlled release of energy for synthesis of ATP 2 H e– ATP Explosive release of heat and light energy ATP Electron transport chain Free energy, G Free energy, G ATP 2 e– Figure 9.5 An introduction to electron transport chains. WHAT ARE THE SWIRLY THINGYS?? 1/2 O2 2 H+ H2O H2O (a) Uncontrolled reaction (b) Cellular respiration

Cell Respiration has three stages:
Glycolysis (breaks down glucose into two molecules of pyruvate) Citric acid cycle (completes the breakdown of glucose) Oxidative phosphorylation (makes ATP and water from oxygen). There are two connected parallel processes here: electron transport and chemiosmosis. 1 glucose + oxygen yields carbon dioxide, water, and ATP. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

ATP accounting is crucial for Cellular Respiration understanding (and AP Biology examinations!)
A small amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation BUT, it is oxidative phosphorylation that accounts for almost 90% of the ATP generated by cellular respiration! Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Electrons carried via NADH ATP Substrate-level phosphorylation
Fig Electrons carried via NADH Glycolysis Glucose Pyruvate Cytosol Figure 9.6 An overview of cellular respiration ATP Substrate-level phosphorylation

Mitochondrial Matrix Cytosol Electrons carried via NADH
Fig Electrons carried via NADH Electrons carried via NADH and FADH2 Glycolysis Citric acid cycle Glucose Pyruvate Mitochondrial Matrix Cytosol Figure 9.6 An overview of cellular respiration ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation

Cytosol Mitochondrial Mitochondrial Matrix Cristae Electrons carried
Fig Electrons carried via NADH Electrons carried via NADH and FADH2 Oxidative phosphorylation: electron transport and chemiosmosis Glycolysis Citric acid cycle Glucose Pyruvate Mitochondrial Mitochondrial Matrix Cristae Cytosol Figure 9.6 An overview of cellular respiration ATP ATP ATP Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation

Glycolysis occurs in the cytoplasm and has two major phases:
Concept 9.2: Glycolysis harvests chemical energy by oxidizing glucose to pyruvate Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate Glycolysis occurs in the cytoplasm and has two major phases: Energy investment phase Energy payoff phase Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Energy investment phase
Fig. 9-8 Energy investment phase Glucose 2 ADP + 2 P 2 ATP used Energy payoff phase 4 ADP + 4 P 4 ATP formed 2 NAD e– + 4 H+ 2 NADH + 2 H+ Figure 9.8 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+

Enzyme Enzyme ADP P Substrate + ATP Product Fig. 9-7
Figure 9.7 Substrate-level phosphorylation Product

Glucose ATP 1 Hexokinase ADP Glucose-6-phosphate Fig. 9-9-1
Figure 9.9 A closer look at glycolysis Glucose-6-phosphate

Glucose-6-phosphate 2 Phosphogluco- isomerase Fructose-6-phosphate
Fig Glucose ATP 1 Hexokinase ADP Glucose-6-phosphate Glucose-6-phosphate 2 Phosphoglucoisomerase 2 Phosphogluco- isomerase Fructose-6-phosphate Figure 9.9 A closer look at glycolysis Fructose-6-phosphate

Fructose- 1, 6-bisphosphate
Fig Glucose ATP 1 1 Hexokinase ADP Fructose-6-phosphate Glucose-6-phosphate 2 2 Phosphoglucoisomerase ATP 3 Phosphofructo- kinase Fructose-6-phosphate ATP 3 3 ADP Phosphofructokinase ADP Figure 9.9 A closer look at glycolysis Fructose- 1, 6-bisphosphate Fructose- 1, 6-bisphosphate

Aldolase Isomerase Fructose- 1, 6-bisphosphate 4 5 Dihydroxyacetone
Fig Glucose ATP 1 Hexokinase ADP Glucose-6-phosphate 2 Phosphoglucoisomerase Fructose- 1, 6-bisphosphate 4 Fructose-6-phosphate Aldolase ATP 3 Phosphofructokinase ADP Figure 9.9 A closer look at glycolysis 5 Isomerase Fructose- 1, 6-bisphosphate 4 Aldolase 5 Isomerase Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate Dihydroxyacetone phosphate Glyceraldehyde- 3-phosphate

2 Glyceraldehyde- 3-phosphate 2 NAD+ 6 Triose phosphate dehydrogenase
Fig 2 NAD+ 6 Triose phosphate dehydrogenase 2 NADH 2 P i + 2 H+ 2 2 1, 3-Bisphosphoglycerate Glyceraldehyde- 3-phosphate 2 2 NAD+ 6 Triose phosphate dehydrogenase 2 P 2 NADH i + 2 H+ Figure 9.9 A closer look at glycolysis 2 1, 3-Bisphosphoglycerate

2 2 ADP 2 ATP 2 3-Phosphoglycerate 1, 3-Bisphosphoglycerate 7
Fig 2 NAD+ 6 Triose phosphate dehydrogenase 2 NADH 2 P i + 2 H+ 2 1, 3-Bisphosphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 1, 3-Bisphosphoglycerate 2 ADP 2 3-Phosphoglycerate 7 Phosphoglycero- kinase 2 ATP Figure 9.9 A closer look at glycolysis 2 3-Phosphoglycerate

2 3-Phosphoglycerate 8 Phosphoglycero- mutase 2 2-Phosphoglycerate
Fig 2 NAD+ 6 Triose phosphate dehydrogenase 2 NADH 2 P i + 2 H+ 2 1, 3-Bisphosphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 3-Phosphoglycerate 2 3-Phosphoglycerate 8 Phosphoglyceromutase 8 Phosphoglycero- mutase 2 2-Phosphoglycerate Figure 9.9 A closer look at glycolysis 2 2-Phosphoglycerate

2 2-Phosphoglycerate Enolase 2 H2O 2 Phosphoenolpyruvate 9 Fig. 9-9-8
2 NAD+ 6 Triose phosphate dehydrogenase 2 NADH 2 P i + 2 H+ 2 1, 3-Bisphosphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 2-Phosphoglycerate 2 3-Phosphoglycerate 8 Phosphoglyceromutase 9 Enolase 2 H2O 2 2-Phosphoglycerate 9 Enolase Figure 9.9 A closer look at glycolysis 2 H2O 2 Phosphoenolpyruvate 2 Phosphoenolpyruvate

2 Phosphoenolpyruvate 2 ADP 10 Pyruvate kinase 2 ATP 2 Pyruvate
Fig 2 NAD+ 6 Triose phosphate dehydrogenase 2 NADH 2 P i + 2 H+ 2 1, 3-Bisphosphoglycerate 2 ADP 7 Phosphoglycerokinase 2 ATP 2 Phosphoenolpyruvate 2 ADP 2 3-Phosphoglycerate 8 10 Phosphoglyceromutase Pyruvate kinase 2 ATP 2 2-Phosphoglycerate 9 Enolase 2 H2O Figure 9.9 A closer look at glycolysis 2 Phosphoenolpyruvate 2 ADP 10 Pyruvate kinase 2 ATP 2 Pyruvate 2 Pyruvate

The mitochondria, compared to the cytosol, is a modern structure.
Concept 9.3: The citric acid cycle completes the energy-yielding oxidation of organic molecules If O2 is present, pyruvate enters the mitochondrion. If there is no O2, anaerobic respiration (which is glycolysis run to completion) occurs. Before the next stage, the citric acid, or Kreb’s cycle, can begin, pyruvate must be converted to acetyl CoA upon entering the mitochondria. The mitochondria, compared to the cytosol, is a modern structure. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

CYTOSOL MITOCHONDRION NAD+ NADH + H+ 2 1 3 Acetyl CoA Pyruvate
Fig. 9-10 CYTOSOL MITOCHONDRION NAD+ NADH + H+ 2 1 3 Acetyl CoA Figure 9.10 Conversion of pyruvate to acetyl CoA, the junction between glycolysis and the citric acid cycle. Note how Acetyl CoA has one less carbon than pyruvate. That carbon has attached to an oxygen molecule, forming CO2, and is exhaled. Acetyl CoA is very reactive, very exergonic. It now heads into the matrix to begin the citric acid cycle. Pyruvate Coenzyme A CO2 Transport protein

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 the pyruvate to the last step in C.R. To put it another way, the cycle has oxidized organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn, PER PYRUVATE, in the mitochondrial matrix. Which means per glucose, that’s x2! Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Pyruvate CO2 NAD+ CoA NADH + H+ Acetyl CoA CoA CoA Citric acid cycle 2
Fig. 9-11 Pyruvate CO2 NAD+ CoA NADH + H+ Acetyl CoA CoA CoA Citric acid cycle 2 CO2 Figure 9.11 An overview of the citric acid cycle. Some ATP is generated here, like in glycolysis, as well as more CO2, but the real stars are the electron carriers, NADH and FADH2, who move on to the last step and are crucial to producing ATP. FADH2 3 NAD+ FAD 3 NADH + 3 H+ ADP + P i ATP

Fig. 9-12-1 Acetyl CoA Oxaloacetate Citrate Citric acid cycle
CoA—SH 1 Oxaloacetate Citrate Citric acid cycle Figure 9.12 A closer look at the citric acid cycle

Fig. 9-12-2 Acetyl CoA Oxaloacetate Citrate Isocitrate Citric acid
CoA—SH 1 H2O Oxaloacetate 2 Citrate Isocitrate Citric acid cycle Figure 9.12 A closer look at the citric acid cycle

Fig. 9-12-3 Acetyl CoA Oxaloacetate Citrate Isocitrate Citric acid
CoA—SH 1 H2O Oxaloacetate 2 Citrate Isocitrate NAD+ Citric acid cycle NADH 3 + H+ CO2 -Keto- glutarate Figure 9.12 A closer look at the citric acid cycle

Citric acid cycle Succinyl CoA
Fig Acetyl CoA CoA—SH 1 H2O Oxaloacetate 2 Citrate Isocitrate NAD+ Citric acid cycle NADH 3 + H+ CO2 CoA—SH -Keto- glutarate Figure 9.12 A closer look at the citric acid cycle 4 CO2 NAD+ NADH Succinyl CoA + H+

Fig Acetyl CoA CoA—SH 1 H2O Oxaloacetate 2 Citrate Isocitrate NAD+ Citric acid cycle NADH 3 + H+ CO2 CoA—SH -Keto- glutarate Figure 9.12 A closer look at the citric acid cycle 4 CoA—SH 5 CO2 NAD+ Succinate P NADH i GTP GDP Succinyl CoA + H+ ADP ATP

Fig Acetyl CoA CoA—SH 1 H2O Oxaloacetate 2 Citrate Isocitrate NAD+ Citric acid cycle NADH 3 + H+ CO2 Fumarate CoA—SH -Keto- glutarate Figure 9.12 A closer look at the citric acid cycle 6 4 CoA—SH FADH2 5 CO2 NAD+ FAD Succinate P NADH i GTP GDP Succinyl CoA + H+ ADP ATP

Fig Acetyl CoA CoA—SH 1 H2O Oxaloacetate 2 Malate Citrate Isocitrate NAD+ Citric acid cycle NADH 3 7 + H+ H2O CO2 Fumarate CoA—SH -Keto- glutarate Figure 9.12 A closer look at the citric acid cycle 6 4 CoA—SH FADH2 5 CO2 NAD+ FAD Succinate P P NADH i GTP GDP Succinyl CoA + H+ ADP ATP

Fig Acetyl CoA CoA—SH NADH +H+ 1 H2O NAD+ 8 Oxaloacetate 2 Malate Citrate Isocitrate NAD+ Citric acid cycle NADH 3 7 + H+ H2O CO2 Fumarate CoA—SH -Keto- glutarate Figure 9.12 A closer look at the citric acid cycle 4 6 CoA—SH FADH2 5 CO2 NAD+ FAD Succinate P NADH i GTP GDP Succinyl CoA + H+ ADP ATP

Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis Following their production in glycolysis and the citric acid cycle, NADH and FADH2 are now used to produce ATP. These two electron carriers donate some of their electrons to the electron transport chain on the mitochondrial cristae. The E.T.C.s function is to break up the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts For the Cell Biology Video ATP Synthase 3D Structure — Side View, go to Animation and Video Files. For the Cell Biology Video ATP Synthase 3D Structure — Top View, go to Animation and Video Files. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

The electrons donated by NADH and FADH2 are passed along a number of proteins on this chain to the end where there is the highly reactive oxygen.. Here, water is made with the addition of these electrons and H+ ions. But where’s the ATP???

Chemiosmosis: The Energy-Coupling Mechanism
The electrons donated in the E.T.C. causes proteins there to actively pump H+ from the mitochondrial matrix to the intermembrane space. H+ then diffuse back across the membrane, passing through channel proteins called ATP synthase. ATP synthase uses the exergonic flow of H+ to drive production of ATP (32-34!) This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work How does having more H+ ions (protons) accumulating on one side of a membrane than another create a pH gradient? How does it create an electrical gradient? Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-13 Figure 9.13 Free-energy change during electron transport
NADH 50 2 e– NAD+ FADH2 2 e– FAD Multiprotein complexes  40 FMN FAD Fe•S  Fe•S Q  Cyt b Fe•S 30 Cyt c1 IV Free energy (G) relative to O2 (kcal/mol) Cyt c Cyt a Cyt a3 20 Figure 9.13 Free-energy change during electron transport e– 10 2 (from NADH or FADH2) 2 H+ + 1/2 O2 H2O

Electron transport chain 2 Chemiosmosis
Fig. 9-16 H+ H+ H+ H+ Protein complex of electron carriers Cyt c V Q   ATP synthase  2 H+ + 1/2O2 H2O FADH2 FAD NADH NAD+ Figure 9.16 Chemiosmosis couples the electron transport chain to ATP synthesis ADP + P ATP i (carrying electrons from food) H+ 1 Electron transport chain 2 Chemiosmosis Oxidative phosphorylation

INTERMEMBRANE SPACE H+ Stator Rotor Internal rod Cata- lytic knob ADP
Fig. 9-14 INTERMEMBRANE SPACE H+ Stator Rotor Internal rod Figure 9.14 ATP synthase, a molecular mill Cata- lytic knob ADP + P ATP i MITOCHONDRIAL MATRIX

Fig. 9-17 Citric acid cycle CYTOSOL Electron shuttles span membrane
MITOCHONDRION 2 NADH or 2 FADH2 2 NADH 2 NADH 6 NADH 2 FADH2 Glycolysis Oxidative phosphorylation: electron transport and chemiosmosis 2 Pyruvate 2 Acetyl CoA Citric acid cycle Glucose + 2 ATP + 2 ATP + about 32 or 34 ATP Figure 9.17 ATP yield per molecule of glucose at each stage of cellular respiration About 36 or 38 ATP Maximum per glucose:

This is the most efficient metabolic process on earth.
About 40% of the energy from a glucose molecule is transferred to ATP during cellular respiration, making ATP. (The rest is lost as heat). This is the most efficient metabolic process on earth. In prokaryotes, oxidative phosphorolation takes place on external cell membranes. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Animation: Fermentation Overview
In alcohol fermentation, pyruvate is converted to ethanol in two steps, with the first releasing CO2 Alcohol fermentation by yeast is used in brewing, winemaking, and baking Animation: Fermentation Overview Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

(a) Alcohol fermentation
Fig. 9-18a 2 ADP + 2 P 2 ATP i Glucose Glycolysis 2 Pyruvate 2 NAD+ 2 NADH 2 CO2 + 2 H+ Chemical Process found in baking, wine making, and brewing!!! 2 Acetaldehyde 2 Ethanol (a) Alcohol fermentation

In lactic acid fermentation, pyruvate is converted lactate in one step, with no release of CO2
Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Do humans FERMENT? 2 ADP + 2 P 2 ATP Glucose Glycolysis 2 NAD+ 2 NADH
Fig. 9-18b 2 ADP + 2 P 2 ATP i Glucose Glycolysis 2 NAD+ 2 NADH + 2 H+ 2 Pyruvate Chemical Process used by some fungi and bacteria to make yogurt, cheese, saurkraut. Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce, meaning, your muscles are working full tilt and there is more ATP needed than can be provided by oxygen. 2 Lactate Do humans FERMENT? (b) Lactic acid fermentation

YES! Human muscle cells use lactic acid fermentation to generate ATP when more O2 is needed than muscle cells can provide And of course, beer, cheese, bread, kimchee, and yogurt makers ferment for a living! Chemical Process used by some fungi and bacteria to make yogurt, cheese, saurkraut. Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce, meaning, your muscles are working full tilt and there is more ATP needed than can be provided by oxygen.

Ethanol or lactate Citric acid cycle
Fig. 9-19 Glucose Glycolysis CYTOSOL Pyruvate O2 present: Aerobic cellular respiration No O2 present: Fermentation MITOCHONDRION Ethanol or lactate Acetyl CoA As organisms we are OBLIGATE AEROBES. However, some tissues, specifically muscle, act as FACULTATIVE AEROBES during LATIC ACID FERMENTATION. HOW do we switch back and forth? Citric acid cycle

Regulation of Cellular Respiration via Feedback Mechanisms
Feedback inhibition is the most common mechanism for control of ATP production. If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down. This is accomplished by regulating activity of enzymes in the pathway. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-21 Glucose AMP Glycolysis Fructose-6-phosphate Stimulates +
Phosphofructokinase – – Fructose-1,6-bisphosphate Inhibits Inhibits Pyruvate ATP Citrate Acetyl CoA Figure 9.21 The control of cellular respiration Citric acid cycle Oxidative phosphorylation

Fermentation and Aerobic Respiration Compared
Both processes use glycolysis to oxidize glucose and other organic fuels to pyruvate The processes have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O2 in cellular respiration Cellular respiration produces 38 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Concept 9.6: Glycolysis and the citric acid cycle connect to many other metabolic pathways
Gycolysis and the citric acid cycle are major intersections to various catabolic and anabolic pathways Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

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; amino groups can feed glycolysis or the citric acid cycle Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fatty acids are broken down by beta oxidation and yield acetyl CoA
Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA) 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 Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Citric acid cycle Oxidative phosphorylation
Fig. 9-20 Proteins Carbohydrates Fats Amino acids Sugars Glycerol Fatty acids Glycolysis Glucose Glyceraldehyde-3- P NH3 Pyruvate Acetyl CoA Figure 9.20 The catabolism of various molecules from food Citric acid cycle Oxidative phosphorylation

The Evolutionary Significance of Glycolysis
Glycolysis occurs in nearly all organisms, and probably evolved in ancient prokaryotes before there was oxygen in the atmosphere Evidence? The oldest fossils of bacteria 3.5 billion years old, but O2 did not appreciably accumulate in the environment until 2.7 bya. The fact that glycolysis occurs in the cytosol, where there are no membrane bound organelles, suggest this processes “great antiquity”. Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Biosynthesis (Anabolic Pathways)
The body uses small molecules to build other substances These small molecules may come directly from food, from glycolysis, or from the citric acid cycle Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Fig. 9-UN5 Inputs Outputs 2 ATP Glycolysis + 2 NADH Glucose 2 Pyruvate

Inputs Outputs S—CoA 2 ATP C O CH3 2 Acetyl CoA 6 NADH O C COO
Fig. 9-UN6 Inputs Outputs S—CoA 2 ATP C O CH3 2 Acetyl CoA 6 NADH O C COO Citric acid cycle CH2 2 FADH2 COO 2 Oxaloacetate

INTER- MEMBRANE SPACE H+ ATP synthase ADP + P ATP MITO- CHONDRIAL
Fig. 9-UN7 INTER- MEMBRANE SPACE H+ ATP synthase ADP + P ATP i MITO- CHONDRIAL MATRIX H+

Fig. 9-UN8 across membrane pH difference Time

Fig. 9-UN9

You should now be able to:
Explain in general terms how redox reactions are involved in energy exchanges Name the three stages of cellular respiration; for each, state the region of the eukaryotic cell where it occurs and the products that result In general terms, explain the role of the electron transport chain in cellular respiration Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Distinguish between fermentation and anaerobic respiration
Explain where and how the respiratory electron transport chain creates a proton gradient Distinguish between fermentation and anaerobic respiration Distinguish between obligate and facultative anaerobes Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Cellular Respiration: Harvesting Chemical Energy

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