Chapter 6 Cellular Respiration

© 2012 Pearson Education, Inc. Lecture by Edward J. Zalisko

PowerPoint Lectures forCampbell Biology: Concepts & Connections, Seventh EditionReece, Taylor, Simon, and Dickey

Chapter 6Chapter 6 How Cells Harvest Chemical Energy

Introduction

In eukaryotes, cellular respiration

– harvests energy from food,

– yields large amounts of ATP, and

– Uses ATP to drive cellular work.

A similar process takes place in many prokaryotic organisms.

© 2012 Pearson Education, Inc.

Figure 6.0_1Chapter 6: Big Ideas

Cellular Respiration:Aerobic Harvesting

of Energy

Stages of CellularRespiration

Fermentation: AnaerobicHarvesting of Energy

Connections BetweenMetabolic Pathways

CELLULAR RESPIRATION: AEROBIC HARVESTING

OF ENERGY


6.1 Photosynthesis and cellular respiration provide energy for life

Life requires energy.

In almost all ecosystems, energy ultimately comes from the sun.

In photosynthesis,

– some of the energy in sunlight is captured by chloroplasts,

– atoms of carbon dioxide and water are rearranged, and

– glucose and oxygen are produced.


6.1 Photosynthesis and cellular respiration provide energy for life

In cellular respiration

– glucose is broken down to carbon dioxide and water and

– the cell captures some of the released energy to make ATP.

Cellular respiration takes place in the mitochondria of eukaryotic cells.


Figure 6.1

Sunlight energy

ECOSYSTEM

Photosynthesisin chloroplasts

Cellular respirationin mitochondria

(for cellularwork)

Heat energy

GlucoseCO2

H2O O2

ATP

Figure 6.1_1

Sunlight energy

ECOSYSTEM

Photosynthesisin chloroplasts

Cellular respirationin mitochondria

(for cellularwork)

Heat energy

GlucoseCO2

H2O O2

ATP

6.2 Breathing supplies O2 for use in cellular respiration and removes CO2

Respiration, as it relates to breathing, and cellular respiration are not the same.

– Respiration, in the breathing sense, refers to an exchange of gases. Usually an organism brings in oxygen from the environment and releases waste CO2.

– Cellular respiration is the aerobic (oxygen requiring) harvesting of energy from food molecules by cells.


Figure 6.2

Breathing

Lungs

BloodstreamCO2 O2

O2 CO2

Muscle cells carrying outCellular Respiration

Glucose O2 CO2 H2O ATP

6.3 Cellular respiration banks energy in ATP molecules

Cellular respiration is an exergonic process that transfers energy from the bonds in glucose to form ATP.

Cellular respiration

– produces up to 32 ATP molecules from each glucose molecule and

– captures only about 34% of the energy originally stored in glucose.

Other foods (organic molecules) can also be used as a source of energy.


Figure 6.3

Glucose Oxygen WaterCarbondioxide

C6H12O6 O2 H2O ATP6 6 6

Heat

CO2

6.4 CONNECTION: The human body uses energy from ATP for all its activities

The average adult human needs about 2,200 kcal of energy per day.

– About 75% of these calories are used to maintain a healthy body.

– The remaining 25% is used to power physical activities.


6.4 CONNECTION: The human body uses energy from ATP for all its activities

A kilocalorie (kcal) is– the quantity of heat required to raise the temperature of

1 kilogram (kg) of water by 1oC,

– the same as a food Calorie, and

– used to measure the nutritional values indicated on food labels.


Figure 6.4

Activity kcal consumed per hourby a 67.5-kg (150-lb) person*

Running (8–9 mph)

Dancing (fast)

Bicycling (10 mph)

Swimming (2 mph)

Walking (4 mph)

Walking (3 mph)

Dancing (slow)

Driving a car

Sitting (writing)

*Not including kcal needed forbody maintenance

979

510

490

408

341

245

204

61

28

6.5 Cells tap energy from electrons “falling” from organic fuels to oxygen

The energy necessary for life is contained in the arrangement of electrons in chemical bonds in organic molecules.

An important question is how do cells extract this energy?



When the carbon-hydrogen bonds of glucose are broken, electrons are transferred to oxygen.

– Oxygen has a strong tendency to attract electrons.

– An electron loses potential energy when it “falls” to oxygen.



Energy can be released from glucose by simply burning it.

The energy is dissipated as heat and light and is not available to living organisms.



On the other hand, cellular respiration is the controlled breakdown of organic molecules.

Energy is

– gradually released in small amounts,

– captured by a biological system, and

– stored in ATP.



The movement of electrons from one molecule to another is an oxidation-reduction reaction, or redox reaction. In a redox reaction,

– the loss of electrons from one substance is called oxidation,

– the addition of electrons to another substance is called reduction,

– a molecule is oxidized when it loses one or more electrons, and

– reduced when it gains one or more electrons.



A cellular respiration equation is helpful to show the changes in hydrogen atom distribution.

Glucose

– loses its hydrogen atoms and

– becomes oxidized to CO2.

Oxygen

– gains hydrogen atoms and

– becomes reduced to H2O.


Figure 6.5A

Glucose Heat

C6H12O6 O2 CO2 H2O ATP6 6 6

Loss of hydrogen atoms(becomes oxidized)

Gain of hydrogen atoms(becomes reduced)


Enzymes are necessary to oxidize glucose and other foods.

NAD+

– is an important enzyme in oxidizing glucose,

– accepts electrons, and

– becomes reduced to NADH.


Figure 6.5B

Becomes oxidized

Becomes reduced

2H

2HNAD NADH

H

H

2 2(carries

2 electrons)


There are other electron “carrier” molecules that function like NAD+.

– They form a staircase where the electrons pass from one to the next down the staircase.

– These electron carriers collectively are called the electron transport chain.

– As electrons are transported down the chain, ATP is generated.


Figure 6.5C

Controlledrelease ofenergy forsynthesisof ATP

NADH

NAD

H

H O2

H2O

2

2

2

ATP

Electron transport chain

21

STAGES OF CELLULAR RESPIRATION


6.6 Overview: Cellular respiration occurs in three main stages

Cellular respiration consists of a sequence of steps that can be divided into three stages.

– Stage 1 – Glycolysis

– Stage 2 – Pyruvate oxidation and citric acid cycle

– Stage 3 – Oxidative phosphorylation



Stage 1: Glycolysis

– occurs in the cytoplasm,

– begins cellular respiration, and

– breaks down glucose into two molecules of a three-carbon compound called pyruvate.



Stage 2: The citric acid cycle

– takes place in mitochondria,

– oxidizes pyruvate to a two-carbon compound, and

– supplies the third stage with electrons.



Stage 3: Oxidative phosphorylation

– involves electrons carried by NADH and FADH2,

– shuttles these electrons to the electron transport chain embedded in the inner mitochondrial membrane,

– involves chemiosmosis, and

– generates ATP through oxidative phosphorylation associated with chemiosmosis.


Figure 6.6

NADH

NADH FADH2

ATP ATPATP

CYTOPLASM

Glycolysis

Electronscarried by NADH

Glucose Pyruvate PyruvateOxidation

Citric AcidCycle

OxidativePhosphorylation

(electron transportand chemiosmosis)

Mitochondrion

Substrate-levelphosphorylation


Oxidativephosphorylation

Figure 6.6_1

NADH

NADH FADH2

ATP ATPATP

CYTOPLASM

Glycolysis

Electronscarried by NADH

Glucose Pyruvate PyruvateOxidation

Citric AcidCycle



Mitochondrion



Oxidativephosphorylation

6.7 Glycolysis harvests chemical energy by oxidizing glucose to pyruvate

In glycolysis,

– a single molecule of glucose is enzymatically cut in half through a series of steps,

– two molecules of pyruvate are produced,

– two molecules of NAD+ are reduced to two molecules of NADH, and

– a net of two molecules of ATP is produced.


Figure 6.7A

Glucose

2 Pyruvate

2 ADP

2 P2 NAD

2 NADH

2 HATP2


ATP is formed in glycolysis by substrate-level phosphorylation during which

– an enzyme transfers a phosphate group from a substrate molecule to ADP and

– ATP is formed.

The compounds that form between the initial reactant, glucose, and the final product, pyruvate, are called intermediates.


Figure 6.7B

Enzyme Enzyme

P

P

ADP

P

ATP

Substrate Product


The steps of glycolysis can be grouped into two main phases.

– In steps 1–4, the energy investment phase,

– energy is consumed as two ATP molecules are used to energize a glucose molecule,

– which is then split into two small sugars that are now primed to release energy.

– In steps 5–9, the energy payoff,

– two NADH molecules are produced for each initial glucose molecule and

– ATP molecules are generated.


Figure 6.7Ca_s1Glucose

Glucose 6-phosphate

Fructose 6-phosphate

Fructose 1,6-bisphosphate

ENERGYINVESTMENT

PHASE

P P

P

P

ADP

ADP

ATP

ATP

StepSteps – A fuelmolecule is energized,using ATP.

3

3

2

1

1

Figure 6.7Ca_s2Glucose

Glucose 6-phosphate

Fructose 6-phosphate

Fructose 1,6-bisphosphate

Glyceraldehyde3-phosphate (G3P)

ENERGYINVESTMENT

PHASE

PP

P P

P

P

ADP

ADP

ATP

ATP

StepSteps – A fuelmolecule is energized,using ATP.

Step A six-carbonintermediate splitsinto two three-carbonintermediates.

4

4

3

3

2

1

1

Figure 6.7Cb_s1

5 5 5Step A redox reactiongenerates NADH.

ENERGYPAYOFFPHASE

1,3-Bisphospho-glycerate

NADH NADH

NADNAD

H H

P P

P

P P

P

P P

Figure 6.7Cb_s2

6 6 6

5 5 5

9

9 9

8 8

7 7

Step A redox reactiongenerates NADH.

Steps – ATP and pyruvateare produced.

ENERGYPAYOFFPHASE

1,3-Bisphospho-glycerate

3-Phospho-glycerate

2-Phospho-glycerate

Phosphoenol-pyruvate (PEP)

Pyruvate

NADH NADH

NADNAD

H H

ADP ADP

ADP ADP

ATP ATP

ATP ATP

H2O H2O

P P

P

P P

P

P

P

P

P P

P

P

P

6.8 Pyruvate is oxidized prior to the citric acid cycle

The pyruvate formed in glycolysis is transported from the cytoplasm into a mitochondrion where

– the citric acid cycle and

– oxidative phosphorylation will occur.


6.8 Pyruvate is oxidized prior to the citric acid cycle

Two molecules of pyruvate are produced for each molecule of glucose that enters glycolysis.

Pyruvate does not enter the citric acid cycle, but undergoes some chemical grooming in which

– a carboxyl group is removed and given off as CO2,

– the two-carbon compound remaining is oxidized while a molecule of NAD+ is reduced to NADH,

– coenzyme A joins with the two-carbon group to form acetyl coenzyme A, abbreviated as acetyl CoA, and

– acetyl CoA enters the citric acid cycle.© 2012 Pearson Education, Inc.

Figure 6.8

Pyruvate

Coenzyme A

Acetyl coenzyme A

NAD NADH H

CoA

CO2

3

2

1

6.9 The citric acid cycle completes the oxidation of organic molecules, generating many NADH and FADH2 molecules

The citric acid cycle

– is also called the Krebs cycle (after the German-British researcher Hans Krebs, who worked out much of this pathway in the 1930s),

– completes the oxidation of organic molecules, and

– generates many NADH and FADH2 molecules.


Figure 6.9AAcetyl CoA

Citric Acid Cycle

CoACoA

CO22

3

3

NAD

3 H

NADH

ADPATP P

FAD

FADH2


During the citric acid cycle

– the two-carbon group of acetyl CoA is added to a four-carbon compound, forming citrate,

– citrate is degraded back to the four-carbon compound,

– two CO2 are released, and

– 1 ATP, 3 NADH, and 1 FADH2 are produced.



Remember that the citric acid cycle processes two molecules of acetyl CoA for each initial glucose.

Thus, after two turns of the citric acid cycle, the overall yield per glucose molecule is

– 2 ATP,

– 6 NADH, and

– 2 FADH2.


Figure 6.9B_s1CoA

CoA

1

Acetyl CoA

Oxaloacetate

Citric Acid Cycle

2 carbons enter cycle

StepAcetyl CoA stokesthe furnace.

1

Figure 6.9B_s2

NADH

NADH

NAD

NAD

H

H

CO2

CO2

ATP

ADP P

CoACoA

321

3

1

2

Acetyl CoA

Oxaloacetate

Citric Acid Cycle


Citrate

leaves cycle

Alpha-ketoglutarate

leaves cycle


Steps –NADH, ATP, and CO2are generated during redox reactions.

Figure 6.9B_s3

NADH

NADH

NAD

NAD

NADNADH

H

H

H

CO2

CO2

ATP

ADP P

FAD

FADH2

CoACoA

321 4 5

34

5

1

2

Acetyl CoA

Oxaloacetate

Citric Acid Cycle


Citrate

leaves cycle

Alpha-ketoglutarate

leaves cycle

Succinate

Malate


Steps –NADH, ATP, and CO2are generated during redox reactions.

Steps –Further redox reactions generateFADH2 and more NADH.

6.10 Most ATP production occurs by oxidative phosphorylation

Oxidative phosphorylation

– involves electron transport and chemiosmosis and

– requires an adequate supply of oxygen.


6.10 Most ATP production occurs by oxidative phosphorylation

Electrons from NADH and FADH2 travel down the electron transport chain to O2.

Oxygen picks up H+ to form water.

Energy released by these redox reactions is used to pump H+ from the mitochondrial matrix into the intermembrane space.

In chemiosmosis, the H+ diffuses back across the inner membrane through ATP synthase complexes, driving the synthesis of ATP.


Figure 6.10

Oxidative Phosphorylation

Electron Transport Chain Chemiosmosis

Mito-chondrialmatrix

Inner mito-chondrialmembrane

Intermem-branespace

Electronflow

Proteincomplexof electroncarriers

Mobileelectroncarriers ATP

synthase

NADH NAD 2 H

FADH2 FAD

O2 H2O

ADP P ATP

12

H

H

H

H

H

H

H

H

H

H

H

I

II

III IV

Figure 6.10_1

H

H

H

H

H

H

H

H

H

H

H

Oxidative Phosphorylation

Electron Transport Chain Chemiosmosis

I

II

IIIIV

NADH NAD 2 H

FADH2 FAD

O2 H2O

ADP P ATP

21

Electronflow

Proteincomplexof electroncarriers

Mobileelectroncarriers ATP

synthase

6.11 CONNECTION: Interrupting cellular respiration can have both harmful and beneficial effects

Three categories of cellular poisons obstruct the process of oxidative phosphorylation. These poisons

1. block the electron transport chain (for example, rotenone, cyanide, and carbon monoxide),

2. inhibit ATP synthase (for example, the antibiotic oligomycin), or

3. make the membrane leaky to hydrogen ions (called uncouplers, examples include dinitrophenol).


Figure 6.11

ATPsynthase

NADNADH

FADH2 FAD

H

H

H

H

H

H H H

2 H

H2O ADP ATPP

O221

Rotenone Cyanide,carbon monoxide

Oligomycin

DNP


Brown fat is– a special type of tissue associated with the generation

of heat and

– more abundant in hibernating mammals and newborn infants.



In brown fat,– the cells are packed full of mitochondria,

– the inner mitochondrial membrane contains an uncoupling protein, which allows H+ to flow back down its concentration gradient without generating ATP, and

– ongoing oxidation of stored fats generates additional heat.


6.12 Review: Each molecule of glucose yields many molecules of ATP

Recall that the energy payoff of cellular respiration involves

1. glycolysis,

2. alteration of pyruvate,

3. the citric acid cycle, and

4. oxidative phosphorylation.


6.12 Review: Each molecule of glucose yields many molecules of ATP

The total yield is about 32 ATP molecules per glucose molecule.

This is about 34% of the potential energy of a glucose molecule.

In addition, water and CO2 are produced.


Figure 6.12

NADH

FADH2

NADH FADH2NADH

orNADH

MitochondrionCYTOPLASM

Electron shuttlesacross membrane

GlycolysisGlucose

2Pyruvate

PyruvateOxidation2 Acetyl

CoA

Citric AcidCycle



Maximumper glucose:

by substrate-levelphosphorylation

by substrate-levelphosphorylation

by oxidativephosphorylation

22

2

2

6 2

ATP 2 about

28 ATP AboutATP32

ATP 2

FERMENTATION: ANAEROBIC HARVESTING OF ENERGY


6.13 Fermentation enables cells to produce ATP without oxygen

Fermentation is a way of harvesting chemical energy that does not require oxygen. Fermentation

– takes advantage of glycolysis,

– produces two ATP molecules per glucose, and

– reduces NAD+ to NADH.

The trick of fermentation is to provide an anaerobic path for recycling NADH back to NAD+.



Your muscle cells and certain bacteria can oxidize NADH through lactic acid fermentation, in which

– NADH is oxidized to NAD+ and

– pyruvate is reduced to lactate.


Animation: Fermentation Overview


Lactate is carried by the blood to the liver, where it is converted back to pyruvate and oxidized in the mitochondria of liver cells.

The dairy industry uses lactic acid fermentation by bacteria to make cheese and yogurt.

Other types of microbial fermentation turn

– soybeans into soy sauce and

– cabbage into sauerkraut.


Figure 6.13A

2 NAD

2 NADH

2 NAD

2 NADH

2 Lactate

2 Pyruvate

Glucose

2 ADP

2 ATP

2 P

Gly

coly

sis


The baking and winemaking industries have used alcohol fermentation for thousands of years.

In this process yeasts (single-celled fungi)

– oxidize NADH back to NAD+ and

– convert pyruvate to CO2 and ethanol.


Figure 6.13B

2 NAD

2 NADH

2 NAD

2 NADH

2 Ethanol

2 Pyruvate

Glucose

2 ADP

2 ATP

2 P

Gly

coly

sis

2 CO2


Obligate anaerobes

– are poisoned by oxygen, requiring anaerobic conditions, and

– live in stagnant ponds and deep soils.

Facultative anaerobes

– include yeasts and many bacteria, and

– can make ATP by fermentation or oxidative phosphorylation.


6.14 EVOLUTION CONNECTION: Glycolysis evolved early in the history of life on Earth

Glycolysis is the universal energy-harvesting process of life.

The role of glycolysis in fermentation and respiration dates back to

– life long before oxygen was present,

– when only prokaryotes inhabited the Earth,

– about 3.5 billion years ago.


6.14 EVOLUTION CONNECTION: Glycolysis evolved early in the history of life on Earth

The ancient history of glycolysis is supported by its

– occurrence in all the domains of life and

– location within the cell, using pathways that do not involve any membrane-bounded organelles.


CONNECTIONS BETWEEN METABOLIC PATHWAYS


6.15 Cells use many kinds of organic molecules as fuel for cellular respiration

Although glucose is considered to be the primary source of sugar for respiration and fermentation, ATP is generated using

– carbohydrates,

– fats, and

– proteins.


6.15 Cells use many kinds of organic molecules as fuel for cellular respiration

Fats make excellent cellular fuel because they

– contain many hydrogen atoms and thus many energy-rich electrons and

– yield more than twice as much ATP per gram than a gram of carbohydrate or protein.


Figure 6.15

Food, such aspeanuts

Sugars Glycerol Fatty acids Amino acids

Aminogroups


CitricAcidCycle

PyruvateOxidation

Acetyl CoA

ATP

Glucose G3P PyruvateGlycolysis

Carbohydrates Fats Proteins

6.16 Food molecules provide raw materials for biosynthesis

Cells use intermediates from cellular respiration for the biosynthesis of other organic molecules.


Figure 6.16

CarbohydratesFatsProteins

Cells, tissues, organisms

Amino acids Fatty acids Glycerol Sugars

Aminogroups

CitricAcidCycle

PyruvateOxidation

Acetyl CoA

ATP neededto drivebiosynthesis

ATP

Glucose SynthesisPyruvate G3P Glucose

6.16 Food molecules provide raw materials for biosynthesis

Metabolic pathways are often regulated by feedback inhibition in which an accumulation of product suppresses the process that produces the product.


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Chapter 6 Cellular Respiration