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Home , Cellular respiration, Electron transport chain, Fermentation, Lactic acid fermentation

CAMPBELL IN FOCUS URRY • CAIN • WASSERMAN • MINORSKY • REECE 7 and

Lecture Presentations by Kathleen Fitzpatrick and Nicole Tunbridge, Simon Fraser University

© 2016 Pearson Education, Inc. SECOND EDITION Is Work

. Living cells require from outside sources . Some , such as the giraffe, obtain energy by eating , and some animals feed on other that eat plants

© 2016 Pearson Education, Inc. Figure 7.1

© 2016 Pearson Education, Inc. . Energy flows into an ecosystem as and as heat

. generates O2 and organic , which are used as for cellular respiration . Cells use chemical energy stored in organic molecules to regenerate ATP, which powers work

© 2016 Pearson Education, Inc. Animation:

© 2016 Pearson Education, Inc. Figure 7.2

Light energy

ECOSYSTEM

Photosynthesis in Organic + O CO2 + H2O molecules 2

Cellular respiration in mitochondria

ATP ATP powers most cellular work

Heat energy

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

© 2016 Pearson Education, Inc. Catabolic Pathways and Production of ATP

. The breakdown of organic molecules is exergonic . Fermentation is a partial degradation of that

occurs without O2 . Aerobic respiration consumes organic molecules

and O2 and yields ATP . is similar to aerobic

respiration but consumes compounds other than O2

© 2016 Pearson Education, Inc. . Cellular respiration includes both aerobic and anaerobic processes but is often used to refer to aerobic respiration . Although , , and are all consumed as fuel, it is helpful to trace cellular respiration with the

C6H12O6 + 6 O2  6 CO2 + 6 H2O + Energy (ATP + heat)

© 2016 Pearson Education, Inc. Reactions: Oxidation and Reduction

. The transfer of during chemical reactions releases energy stored in organic molecules . This released energy is ultimately used to synthesize ATP

© 2016 Pearson Education, Inc. 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. Figure 7.UN01

becomes oxidized (loses electron)

becomes reduced (gains electron)

© 2016 Pearson Education, Inc. Figure 7.UN02

becomes oxidized

becomes reduced

© 2016 Pearson Education, Inc. . The is called the . The 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

and O2

© 2016 Pearson Education, Inc. Figure 7.3

Reactants Products becomes oxidized

becomes reduced

Methane (reducing (oxidizing agent) agent)

© 2016 Pearson Education, Inc. . Redox reactions that move electrons closer to electronegative atoms, like oxygen, release chemical energy that can be put to work

© 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 , 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. Figure 7.UN03

becomes oxidized

becomes reduced

© 2016 Pearson Education, Inc. Stepwise Energy Harvest via NAD+ and the . 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. . called facilitate the transfer of two electrons and one to NAD+ . One hydrogen ion is released in this process

© 2016 Pearson Education, Inc. Figure 7.4

2 e + 2 H+ 2 e + H+ NAD+ NADH H+ Reduction of NAD+ 2[H] H+ (from food) Oxidation of NADH Nicotinamide (oxidized form) (reduced form)

© 2016 Pearson Education, Inc. Figure 7.4-1 NAD+

Nicotinamide (oxidized form)

© 2016 Pearson Education, Inc. Figure 7.4-2

2 e + 2 H+ 2 e + H+ NADH H+ Dehydrogenase Reduction of NAD+ 2[H] H+ (from food) Oxidation of NADH Nicotinamide (reduced form)

© 2016 Pearson Education, Inc. Figure 7.UN04

Dehydrogenase

© 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. Figure 7.5

1 1 H2 + /2 O2 2 H + /2 O2

Controlled 2 H+ + 2 e release of energy ATP G G ATP Explosive release ATP Free energy, energy, Free Free energy, energy, Free 2 e  1/ O 2 H+ 2 2

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 . breaks down glucose into two molecules of pyruvate in the . Pyruvate oxidation and the citric cycle completes the breakdown of glucose in the . Oxidative accounts for most of the ATP synthesis and occurs in the inner membrane of the mitochondria

© 2016 Pearson Education, Inc. Figure 7.UN05

1. GLYCOLYSIS (color-coded blue throughout the chapter) 2. PYRUVATE OXIDATION and the CYCLE (color-coded orange)

3. OXIDATIVE PHOSPHORYLATION: Electron transport and (color-coded purple)

© 2016 Pearson Education, Inc. Figure 7.6-s1

Electrons via NADH

GLYCOLYSIS

Glucose Pyruvate

CYTOSOL

ATP

Substrate-level

© 2016 Pearson Education, Inc. Figure 7.6-s2

Electrons Electrons via NADH via NADH and FADH2

GLYCOLYSIS PYRUVATE OXIDATION CITRIC ACID Glucose Pyruvate Acetyl CoA CYCLE

CYTOSOL MITOCHONDRION

ATP ATP

Substrate-level Substrate-level

© 2016 Pearson Education, Inc. Figure 7.6-s3

Electrons Electrons via NADH via NADH and FADH2

GLYCOLYSIS PYRUVATE OXIDATIVE OXIDATION CITRIC PHOSPHORYLATION ACID Glucose Pyruvate Acetyl CoA CYCLE (Electron transport and chemiosmosis)

CYTOSOL MITOCHONDRION

ATP ATP ATP

Substrate-level Substrate-level Oxidative

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

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

© 2016 Pearson Education, Inc. . For each molecule of glucose degraded to CO2 and water by respiration, the makes up to 32 molecules of ATP

© 2016 Pearson Education, Inc. Figure 7.7

Enzyme Enzyme

ADP P Substrate ATP 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 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. Figure 7.UN06

CITRIC OXIDATIVE PYRUVATE GLYCOLYSIS ACID PHOSPHORYL- OXIDATION CYCLE ATION

ATP

© 2016 Pearson Education, Inc. Figure 7.8 Energy Investment Phase Glucose

2 ATP used 2 ADP + 2 P

Energy Payoff Phase

4 ADP + 4 P 4 ATP formed

+ e + + 2 NAD + 4 + 4 H 2 NADH + 2 H

2 Pyruvate + 2 H2O

Net Glucose 2 Pyruvate + 2 H2O 4 ATP formed  2 ATP used 2 ATP 2 NAD+ + 4 e + 4 H+ 2 NADH + 2 H+ © 2016 Pearson Education, Inc. Figure 7.9-1

GLYCOLYSIS: Energy Investment Phase

Glyceraldehyde 3-phosphate (G3P)

ATP Glucose ATP Fructose Glucose 6-phosphate 6-phosphate 1,6-bisphosphate ADP ADP

Hexokinase Phosphogluco- Phospho- Aldolase Dihydroxyacetone isomerase fructokinase phosphate (DHAP)

© 2016 Pearson Education, Inc. Figure 7.9-1a-s1

GLYCOLYSIS: Energy Investment Phase

Glucose

© 2016 Pearson Education, Inc. Figure 7.9-1a-s2

GLYCOLYSIS: Energy Investment Phase

ATP Glucose Glucose 6-phosphate ADP

Hexokinase

© 2016 Pearson Education, Inc. Figure 7.9-1a-s3

GLYCOLYSIS: Energy Investment Phase

ATP Glucose Fructose Glucose 6-phosphate 6-phosphate ADP

Hexokinase Phosphogluco- isomerase

© 2016 Pearson Education, Inc. Figure 7.9-1b-s1

GLYCOLYSIS: Energy Investment Phase

Fructose 6-phosphate

© 2016 Pearson Education, Inc. Figure 7.9-1b-s2

GLYCOLYSIS: Energy Investment Phase

Fructose ATP Fructose 6-phosphate 1,6-bisphosphate ADP

Phospho- fructokinase

© 2016 Pearson Education, Inc. Figure 7.9-1b-s3

GLYCOLYSIS: Energy Investment Phase

Glyceraldehyde 3-phosphate (G3P)

Fructose ATP Fructose 6-phosphate 1,6-bisphosphate ADP Isomerase

Phospho- Aldolase Dihydroxyacetone fructokinase phosphate (DHAP)

© 2016 Pearson Education, Inc. Figure 7.9-2

GLYCOLYSIS: Energy Payoff Phase

2 ATP 2 ATP 2 NADH 2 H O Glyceraldehyde 2 2 ADP + + 2 ADP 3-phosphate (G3P) 2 NA D + 2 H 2 2 2 2 2

Triose Phospho- Phospho- Pyruvate glyceromutase phosphate 2 P glycerokinase dehydrogenase i 1,3-Bisphospho- 3-Phospho- 2-Phospho- Phosphoenol- Pyruvate glycerate glycerate glycerate pyruvate (PEP)

© 2016 Pearson Education, Inc. Figure 7.9-2a-s1

GLYCOLYSIS: Energy Payoff Phase

Glyceraldehyde 3-phosphate (G3P)

Isomerase

Aldolase Dihydroxyacetone phosphate (DHAP)

© 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 2 P i Isomerase dehydrogenase 1,3-Bisphospho- glycerate Aldolase Dihydroxyacetone phosphate (DHAP)

© 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 Phospho- phosphate glycerokinase 2 P i Isomerase dehydrogenase 1,3-Bisphospho- 3-Phospho- glycerate glycerate Aldolase Dihydroxyacetone phosphate (DHAP)

© 2016 Pearson Education, Inc. Figure 7.9-2b-s1

GLYCOLYSIS: Energy Payoff Phase

2

3-Phospho- glycerate

© 2016 Pearson Education, Inc. Figure 7.9-2b-s2

GLYCOLYSIS: Energy Payoff Phase

2 H2O 2 2 2

Phospho- Enolase glyceromutase 3-Phospho- 2-Phospho- Phosphoenol- glycerate glycerate 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- Enolase Pyruvate glyceromutase kinase 3-Phospho- 2-Phospho- Phosphoenol- Pyruvate glycerate glycerate pyruvate (PEP)

© 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. Figure 7.UN07

CITRIC OXIDATIVE PYRUVATE GLYCOLYSIS ACID PHOSPHORYL- OXIDATION CYCLE ATION

ATP

© 2016 Pearson Education, Inc. Figure 7.10 Pyruvate CYTOSOL (from glycolysis, 2 molecules per glucose)

PYRUVATE OXIDATION

CO2 NAD+ CoA NADH + H+ Acetyl CoA CoA

CoA

CITRIC ACID CYCLE 2 CO2

+ FADH2 3 NAD

FAD 3 NADH + 3 H+ ADP + P i ATP MITOCHONDRION

© 2016 Pearson Education, Inc. Figure 7.10-1 Pyruvate CYTOSOL (from glycolysis, 2 molecules per glucose)

PYRUVATE OXIDATION

CO2 NAD+ CoA NADH + H+ Acetyl CoA CoA MITOCHONDRION © 2016 Pearson Education, Inc. Figure 7.10-2 Acetyl CoA CoA

CoA

CITRIC ACID CYCLE 2 CO2

+ FADH2 3 NAD

FAD 3 NADH + 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. . 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. Figure 7.UN08

CITRIC OXIDATIVE PYRUVATE GLYCOLYSIS ACID PHOSPHORYL- OXIDATION CYCLE ATION

ATP

© 2016 Pearson Education, Inc. Figure 7.11-s1

Acetyl CoA

CoA-SH

H2O

Oxaloacetate

Citrate Isocitrate CITRIC ACID CYCLE

© 2016 Pearson Education, Inc. Figure 7.11-s2

Acetyl CoA

CoA-SH

H2O

Oxaloacetate

Citrate Isocitrate CITRIC NAD+ NADH ACID + H+ CYCLE CO2

a-Ketoglutarate

© 2016 Pearson Education, Inc. Figure 7.11-s3

Acetyl CoA

CoA-SH

H2O

Oxaloacetate

Citrate Isocitrate CITRIC NAD+ NADH ACID + H+ CYCLE CO2

CoA-SH a-Ketoglutarate

CO NAD+ 2

NADH + H+ Succinyl CoA

© 2016 Pearson Education, Inc. Figure 7.11-s4

Acetyl CoA

CoA-SH

H2O

Oxaloacetate

Citrate Isocitrate CITRIC NAD+ NADH ACID + H+ CYCLE CO2

CoA-SH a-Ketoglutarate

CoA-SH

CO NAD+ 2

NADH Succinate P i + H+ GTP GDP Succinyl CoA ADP

ATP

© 2016 Pearson Education, Inc. Figure 7.11-s5

Acetyl CoA

CoA-SH

H2O

Oxaloacetate

Citrate Isocitrate CITRIC NAD+ NADH ACID + H+ CYCLE CO2

Fumarate CoA-SH a-Ketoglutarate

CoA-SH

FADH CO 2 NAD+ 2 FAD NADH Succinate P i + H+ GTP GDP Succinyl CoA ADP

ATP

© 2016 Pearson Education, Inc. Figure 7.11-s6

Acetyl CoA

CoA-SH

NADH H O + H+ 2 NAD+ Oxaloacetate

Malate Citrate Isocitrate CITRIC NAD+ NADH ACID + H+ H2O CYCLE CO2

Fumarate CoA-SH a-Ketoglutarate

CoA-SH

FADH CO 2 NAD+ 2 FAD NADH Succinate P i + H+ GTP GDP Succinyl CoA ADP

ATP

© 2016 Pearson Education, Inc. Figure 7.11-1

Start: Acetyl CoA adds its two-carbon group to oxaloacetate, producing citrate; this is a highly exergonic reaction. Acetyl CoA

CoA-SH

H2O

Oxaloacetate

Citrate Isocitrate

© 2016 Pearson Education, Inc. Figure 7.11-2

Isocitrate NAD+ Redox reaction: Isocitrate is oxidized; NADH NAD+ is reduced. + H+

CO2 CO2 release

CoA-SH a-Ketoglutarate

CO2 CO release NAD+ 2 Redox reaction: NADH After CO2 release, the resulting + H+ four-carbon molecule is oxidized Succinyl (reducing NAD+), then made CoA reactive by addition of CoA. © 2016 Pearson Education, Inc. Figure 7.11-3

Fumarate

CoA-SH

FADH2 FAD Redox reaction: Succinate is oxidized; Succinate P i FAD is reduced. GTP GDP Succinyl CoA ADP ATP formation ATP

© 2016 Pearson Education, Inc. Figure 7.11-4

Redox reaction: Malate is oxidized; NADH NAD+ is reduced. + H+ NAD+ Oxaloacetate

Malate

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. 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. . Electrons are transferred from NADH or FADH2 to the electron transport chain . Electrons are passed through a number of proteins including (each with an 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. Figure 7.UN09

CITRIC OXIDATIVE PYRUVATE GLYCOLYSIS ACID PHOSPHORYL- OXIDATION CYCLE ATION

ATP

© 2016 Pearson Education, Inc. Figure 7.12 NADH (least electronegative) 50 2 e NAD+

FADH2 e Complexes I-IV 2 FAD 40 FMN I Fe S II Fe•S • (kcal/mol)

Q 2 III Cyt b 30 Fe•S c Cyt 1 IV Cyt c Cyt a

) relative ) relative to O a Electron transport Cyt 3 G 20 chain

e 10 2 Free energy (

2 H+ + ½ O 0 2 (most electronegative)

H2O © 2016 Pearson Education, Inc. Figure 7.12-1 NADH (least electronegative) 50 2 e NAD+

FADH2 e Complexes I-IV 2 FAD

(kcal/mol) I 40 FMN 2 Fe S II Fe•S • Q III Cyt b 30 Fe•S c Cyt 1 ) relative ) relative to O IV

G Cyt c Cyt a Electron transport a Cyt 3 20 chain Free energy (

e 10 2

© 2016 Pearson Education, Inc. Figure 7.12-2

30 Fe•S Cyt c 1 IV Cyt c Electron transport a (kcal/mol) Cyt

2 chain a Cyt 3 20

 ) relative to O to relative ) 2 e

G 10

2 H+ + ½ O 0 2

Free energy ( energy Free (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 . H+ then moves back across the membrane, passing through the 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. Figure 7.13 Intermembrane Inner space mitochondrial Mitochondrial membrane matrix

INTERMEMBRANE SPACE

H+ Stator Rotor

Internal rod Catalytic knob

ADP + ATP P i MITOCHONDRIAL MATRIX (a) The ATP synthase (b) Computer model of ATP synthase © 2016 Pearson Education, Inc. Figure 7.13-1 H+ INTERMEMBRANE SPACE Stator Rotor

Internal rod

Catalytic knob

ADP +

MITOCHONDRIAL MATRIX P i ATP

(a) The ATP synthase protein complex © 2016 Pearson Education, Inc. Figure 7.13-2

(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 -motive force, emphasizing its capacity to do work

© 2016 Pearson Education, Inc. Figure 7.UN09

CITRIC OXIDATIVE PYRUVATE GLYCOLYSIS ACID PHOSPHORYL- OXIDATION CYCLE ATION

ATP

© 2016 Pearson Education, Inc. Figure 7.14

H+ H+ ATP H+ synthase H+ Protein complex Cyt c of electron carriers IV Q I III

II 2 H+ + ½ O H O FAD 2 2 FADH2

NADH NAD+ ADP + P i ATP (carrying electrons from food) H+

Electron transport chain Chemiosmosis

Oxidative phosphorylation

© 2016 Pearson Education, Inc. Figure 7.14-1

H+ H+ H+

Protein complex Cyt c of electron carriers

IV Q I III

II 2 H+ + ½ O H O FAD 2 2 FADH2

NADH NAD+ (carrying electrons from food)

Electron transport chain

© 2016 Pearson Education, Inc. Figure 7.14-2 ATP synthase H+

ADP + P i ATP

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. Figure 7.15

CYTOSOL Electron shuttles MITOCHONDRION span membrane 2 NADH or

2 FADH2

2 NADH 2 NADH 6 NADH 2 FADH2

GLYCOLYSIS PYRUVATE OXIDATION OXIDATIVE CITRIC PHOSPHORYLATION ACID Glucose 2 Pyruvate 2 Acetyl CoA CYCLE (Electron transport and chemiosmosis)

+ 2 ATP + 2 ATP + about 26 or 28 ATP

Maximum per glucose: About 30 or 32 ATP

© 2016 Pearson Education, Inc. Figure 7.15-1

Electron shuttles span membrane 2 NADH or

2 FADH2

2 NADH

GLYCOLYSIS

Glucose 2 Pyruvate

+ 2 ATP

© 2016 Pearson Education, Inc. Figure 7.15-2

2 NADH 6 NADH 2 FADH2

PYRUVATE OXIDATION CITRIC ACID 2 Acetyl CoA CYCLE

+ 2 ATP

© 2016 Pearson Education, Inc. Figure 7.15-3

2 NADH or

2 FADH2

2 NADH 6 NADH 2 FADH2

OXIDATIVE PHOSPHORYLATION (Electron transport and chemiosmosis)

+ about 26 or 28 ATP

© 2016 Pearson Education, Inc. Figure 7.15-4

Maximum per glucose: About 30 or 32 ATP

© 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. . Anaerobic respiration uses an electron transport

chain with a final electron acceptor other than O2, for example, . Fermentation uses substrate-level phosphorylation instead of an electron transport chain to generate ATP

© 2016 Pearson Education, Inc. Types of Fermentation

. Fermentation consists of glycolysis plus reactions that regenerate NAD+, which can be reused by glycolysis . Two common types are fermentation and fermentation

© 2016 Pearson Education, Inc. . In alcohol fermentation, pyruvate is converted to in two steps

. The first step releases CO2 from pyruvate, and the second step reduces the resulting to ethanol . Alcohol fermentation by is used in , , and baking

© 2016 Pearson Education, Inc. Animation: Fermentation Overview

© 2016 Pearson Education, Inc. Figure 7.16-1

2 ADP + 2 P i 2 ATP

Glucose GLYCOLYSIS

2 Pyruvate

2 NAD+ 2 NADH 2 CO2 + 2 H+

2 Ethanol 2 Acetaldehyde

(a) Alcohol fermentation © 2016 Pearson Education, Inc. . In , pyruvate is reduced by NADH, forming lactate as an end product, with no

release of CO2 . Lactic acid fermentation by some fungi and is used to make and . Human muscle cells use lactic acid fermentation to

generate ATP when O2 is scarce

© 2016 Pearson Education, Inc. Figure 7.16-2

2 ADP + 2 P i 2 ATP

Glucose GLYCOLYSIS

2 NAD+ 2 NADH + 2 H+ 2 Pyruvate

2 Lactate (b) Lactic acid fermentation © 2016 Pearson Education, Inc. Figure 7.16

2 ADP + 2 P 2 ATP i 2 ADP + 2 P i 2 ATP

Glucose GLYCOLYSIS Glucose GLYCOLYSIS

2 Pyruvate

2 NAD+ 2 NADH + 2 CO2 2 NAD 2 NADH + 2 H+ + 2 H+ 2 Pyruvate

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. . Cellular respiration produces about 32 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule

© 2016 Pearson Education, Inc. . 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. Figure 7.17 Glucose

Glycolysis CYTOSOL

Pyruvate

No O2 present: O2 present: Fermentation Aerobic cellular respiration

MITOCHONDRION Ethanol, Acetyl CoA lactate, or other products CITRIC ACID CYCLE

© 2016 Pearson Education, Inc. The Evolutionary Significance of Glycolysis

. Glycolysis is the most common among organisms on Earth, indicating that it evolved early in the history of life . Early 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. 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. The Versatility of

. 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 and amino groups must be removed before amino acids can feed glycolysis or the citric acid cycle

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

© 2016 Pearson Education, Inc. Figure 7.18-s1 Proteins Carbohydrates Fats

Amino Sugars Glycerol Fatty acids acids

© 2016 Pearson Education, Inc. Figure 7.18-s2 Proteins Carbohydrates Fats

Amino Sugars Glycerol Fatty acids acids

GLYCOLYSIS Glucose

Glyceraldehyde 3- P

NH3 Pyruvate

© 2016 Pearson Education, Inc. Figure 7.18-s3 Proteins Carbohydrates Fats

Amino Sugars Glycerol Fatty acids acids

GLYCOLYSIS Glucose

Glyceraldehyde 3- P

NH3 Pyruvate

Acetyl CoA

© 2016 Pearson Education, Inc. Figure 7.18-s4 Proteins Carbohydrates Fats

Amino Sugars Glycerol Fatty acids acids

GLYCOLYSIS Glucose

Glyceraldehyde 3- P

NH3 Pyruvate

Acetyl CoA

CITRIC ACID CYCLE

© 2016 Pearson Education, Inc. Figure 7.18-s5 Proteins Carbohydrates Fats

Amino Sugars Glycerol Fatty acids acids

GLYCOLYSIS Glucose

Glyceraldehyde 3- P

NH3 Pyruvate

Acetyl CoA

CITRIC OXIDATIVE ACID CYCLE PHOSPHORYLATION

© 2016 Pearson Education, Inc. (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. Figure 7.UN10-1

© 2016 Pearson Education, Inc. Figure 7.UN11

Inputs Outputs

GLYCOLYSIS Glucose 2 Pyruvate 2 ATP 2 NADH

© 2016 Pearson Education, Inc. Figure 7.UN12

Inputs Outputs

2 Pyruvate 2 Acetyl CoA 2 ATP 8 NADH CITRIC 2 Oxaloacetate ACID CYCLE 6 CO2 2 F A DH2

© 2016 Pearson Education, Inc. Figure 7.UN13

INTERMEMBRANE + SPACE H H+

H+ Cyt c Protein complex of electron carriers IV Q I III II + 2 H + ½ O2 H2O FA DH2 FAD

NAD+ NA DH MITOCHONDRIAL MATRIX (carrying electrons from food)

© 2016 Pearson Education, Inc. Figure 7.UN14

INTER- MEMBRANE SPACE H+

MITO CHONDRIAL MATRIX ATP synthase

+ ADP + P i H ATP

© 2016 Pearson Education, Inc. Figure 7.UN15 pH difference

across across membrane Time

© 2016 Pearson Education, Inc. Figure 7.UN16

Low ATP concentration activity activity

High ATP

Phosphofructokinase Phosphofructokinase concentration

Fructose 6-phosphate concentration

© 2016 Pearson Education, Inc.