How Cells How Cells Release Release

Chemical EnergyChemical EnergyChapter 7Chapter 7

Impacts, IssuesImpacts, IssuesWhen Mitochondria Spin When Mitochondria Spin

Their WheelsTheir Wheels MitochondriaMitochondria are the organelles are the organelles

responsible for releasing the energy responsible for releasing the energy stored in foodsstored in foods

In In Luft’s syndromeLuft’s syndrome, the mitochondria are , the mitochondria are active in oxygen consumption, but with active in oxygen consumption, but with little ATP formation to show for itlittle ATP formation to show for it

In In Friedreich’s ataxiaFriedreich’s ataxia, too much iron in , too much iron in the mitochondria causes an accumulation the mitochondria causes an accumulation of free radicals that attack valuable of free radicals that attack valuable molecules of lifemolecules of life

The ImpactThe Impact

Proper, or improper, Proper, or improper, functioning of functioning of mitochondria is the mitochondria is the difference between difference between health and diseasehealth and disease

Section 7.1Section 7.1

Overview of Overview of

Energy-Releasing Energy-Releasing PathwaysPathways

Producing the Universal Producing the Universal Currency of Life Currency of Life

All All energy-releasingenergy-releasing pathways: pathways: require characteristic starting require characteristic starting

materialsmaterials yield predictable products and yield predictable products and

by-products by-products produce ATP produce ATP

Photosynthesizers get energy from Photosynthesizers get energy from the sunthe sun

Animals get energy second- or Animals get energy second- or third-hand from plants or other third-hand from plants or other organismsorganisms

Regardless, Regardless, the energy is the energy is converted to the chemical bond converted to the chemical bond energy of ATPenergy of ATP

ATP Is Universal ATP Is Universal Energy SourceEnergy Source

Making ATPMaking ATP

Plants make ATP during Plants make ATP during

photosynthesisphotosynthesis

Cells of Cells of allall organisms make organisms make

ATP by breaking down ATP by breaking down

carbohydrates, fats, and proteincarbohydrates, fats, and protein

Main Types of Main Types of Energy-Releasing Energy-Releasing

Pathways Pathways Aerobic pathwaysAerobic pathways Evolved laterEvolved later Require oxygenRequire oxygen Start with Start with

glycolysis in glycolysis in cytoplasmcytoplasm

Completed in Completed in mitochondriamitochondria

Anaerobic Anaerobic pathwayspathways

Evolved firstEvolved first Don’t require Don’t require

oxygenoxygen Start with Start with

glycolysis in glycolysis in cytoplasmcytoplasm

Completed in Completed in cytoplasmcytoplasm

Energy-Releasing Pathways

Overview of Aerobic Overview of Aerobic RespirationRespiration

CC66HH12120066 + 6O + 6O22 6CO6CO22 + +

6H6H2200

glucose oxygen carbon glucose oxygen carbon dioxide waterdioxide water

Overview of Aerobic Respirationcytoplasm

mitochondrion

GLYCOLYSIS

ELECTRON TRANSPORT

PHOSPHORYLATION

KrebsCycle ATP

ATP

energy input to start reactions

2 CO2

4 CO2

2

32

water

2 NADH

8 NADH

2 FADH2

2 NADH2 pyruvate

e- + H+

e- + oxygen

(2 ATP net)

glucose

TYPICAL ENERGY YIELD: 36 ATP

e-

e- + H+

e- + H+

ATP

H+

e- + H+

ATP2

Main Pathways Start Main Pathways Start with Glycolysiswith Glycolysis

GlycolysisGlycolysis occurs in cytoplasm occurs in cytoplasm Reactions are catalyzed by Reactions are catalyzed by

enzymesenzymes

GlucoseGlucose 2 Pyruvate2 Pyruvate

(six carbons) (six carbons) (three carbons)(three carbons)

p.106a

Three Series of Reactions Three Series of Reactions Are Required for Aerobic Are Required for Aerobic

RespirationRespiration GlycolysisGlycolysis is the breakdown is the breakdown

of glucose to of glucose to pyruvatepyruvateSmall amountsSmall amounts of ATP are of ATP are

generatedgenerated

Three Series of Reactions Three Series of Reactions Are Required for Aerobic Are Required for Aerobic

RespirationRespiration The The Krebs cycleKrebs cycle degrades degrades

pyruvate to COpyruvate to CO22 and water; and water; NAD and FAD accept HNAD and FAD accept H++ ions ions

and electrons to be carried to and electrons to be carried to the electron transfer chainthe electron transfer chain

Small amountsSmall amounts of ATP are of ATP are generatedgenerated

Three Series of Reactions Three Series of Reactions Are Required for Aerobic Are Required for Aerobic

RespirationRespiration Electron transfer Electron transfer

phosphorylationphosphorylation processes processes the Hthe H++ ions and electrons to ions and electrons to generate lots of ATPgenerate lots of ATPOxygenOxygen is the final electron is the final electron

acceptoracceptor

The Role of CoenzymesThe Role of Coenzymes

NADNAD++ and FAD accept electrons and and FAD accept electrons and hydrogen from intermediates during hydrogen from intermediates during the first two stagesthe first two stages

When reduced, they are NADH and When reduced, they are NADH and FADHFADH22

In the third stage, these coenzymes In the third stage, these coenzymes deliver the electrons and hydrogen to deliver the electrons and hydrogen to the transfer chainthe transfer chain

Overview of Aerobic Respirationcytoplasm

mitochondrion

GLYCOLYSIS

ELECTRON TRANSPORT

PHOSPHORYLATION

KrebsCycle ATP

ATP

energy input to start reactions

2 CO2

4 CO2

2

32

water

2 NADH

8 NADH

2 FADH2

2 NADH2 pyruvate

e- + H+

e- + oxygen

(2 ATP net)

glucose

TYPICAL ENERGY YIELD: 36 ATP

e-

e- + H+

e- + H+

ATP

H+

e- + H+

ATP2

Section 7.2Section 7.2

The First Stage: The First Stage: GlycolysisGlycolysis

A simple sugarA simple sugar

(C(C66HH1212OO66))

Atoms held Atoms held together by together by covalent bondscovalent bonds

Glucose Glucose

Glycolysis Occurs Glycolysis Occurs in Two Stages in Two Stages

Energy-requiringEnergy-requiring steps stepsATP energy activates glucose ATP energy activates glucose

and its six-carbon derivativesand its six-carbon derivatives

Glycolysis Occurs Glycolysis Occurs in Two Stages in Two Stages

Energy-releasingEnergy-releasing steps stepsThe products of the first part The products of the first part

are split into 3-carbon are split into 3-carbon pyruvatepyruvate molecules molecules

ATPATP and and NADHNADH form form

Energy-Requiring Steps

ATP

ATP

2 ATP invested

ENERGY-REQUIRING STEPSOF GLYCOLYSIS

glucose

ADP

ADP

P

P

P

P

glucose–6–phosphate

fructose–6–phosphate

fructose–1,6–bisphosphate DHAP

Energy-Releasing Steps

ATP

PGAL PGAL

ATP

NADH NADH

ATP ATP

2 ATP produced

ENERGY-RELEASING STEPS OF GLYCOLYSIS

2 ATP produced

NAD+

Pi

NAD+

Pi

3-phosphoglycerate 3-phosphoglycerate

2-phosphoglycerate 2-phosphoglycerate

PEP PEP

ADP ADP

1,3-bisphosphoglycerate 1,3-bisphosphoglycerateP P P P

P P

P P

P P

pyruvate pyruvate

to second set of reactions

substrate-level phosphorylation

substrate-level phosphorylation

H2O H2O

ADP ADP

Glycolysis in a NutshellGlycolysis in a Nutshell Glucose is first Glucose is first phosphorylatedphosphorylated in in

energy-requiring steps, then split to energy-requiring steps, then split to form two molecules of form two molecules of PGALPGAL

Enzymes remove HEnzymes remove H++ and electrons and electrons from PGAL to change NADfrom PGAL to change NAD++ to NADH to NADH (which is used later in electron (which is used later in electron transfertransfer PGAL is converted eventually to PGAL is converted eventually to

pyruvatepyruvate By By substrate-level phosphorylationsubstrate-level phosphorylation, ,

fourfour ATP are produced ATP are produced

Substrate-level What?Substrate-level What?

Substrate-level phosphorylation Substrate-level phosphorylation means that there is a means that there is a directdirect transfer transfer of a of a phosphate groupphosphate group from the from the substrate of a reaction to some substrate of a reaction to some other molecule – in this case, ADPother molecule – in this case, ADP

SubstrateSubstrate is a reactant in a reaction is a reactant in a reaction – the substance being acted upon, – the substance being acted upon, for example, by an enzymefor example, by an enzyme

Net Energy Yield Net Energy Yield from Glycolysisfrom Glycolysis

Energy requiring stepsEnergy requiring steps:: 2 ATP invested2 ATP invested

Energy releasing stepsEnergy releasing steps::2 NADH formed 2 NADH formed 4 ATP formed4 ATP formed

Net yield is 2 ATP and 2 Net yield is 2 ATP and 2 NADHNADH

Section 7.3Section 7.3

Second Stage of Second Stage of Aerobic RespirationAerobic Respiration

Occur in the Occur in the mitochondriamitochondria

PyruvatePyruvate is is broken down to broken down to carbon dioxidecarbon dioxide

More ATP is More ATP is formedformed

More More coenzymes are coenzymes are reducedreduced

Second-Stage Reactions Second-Stage Reactions

innermitochondrial

membrane

outermitochondrial

membrane

innercompartment

outercompartment

Fig. 7-5b, p.112

Second Second Stage of Stage of Aerobic Aerobic RespiratRespirationion

Two Parts of Second Two Parts of Second Stage Stage

Preparatory reactionsPreparatory reactionsPyruvate is oxidized into two-Pyruvate is oxidized into two-

carbon acetyl units and carbon acetyl units and carbon dioxidecarbon dioxide

NADNAD++ is reduced is reduced Krebs cycleKrebs cycle

The acetyl units are oxidized The acetyl units are oxidized to carbon dioxideto carbon dioxide

NADNAD+ + and FAD are reducedand FAD are reduced

pyruvate + coenzyme A + NADpyruvate + coenzyme A + NAD++

acetyl-CoA + NADH + COacetyl-CoA + NADH + CO22

One of the carbons from pyruvate is One of the carbons from pyruvate is released in COreleased in CO22

Two carbons are attached to coenzyme Two carbons are attached to coenzyme A and continue on to the Krebs cycleA and continue on to the Krebs cycle

Preparatory ReactionsPreparatory Reactions

What Is Acetyl-CoA?What Is Acetyl-CoA?

A two-carbon acetyl group A two-carbon acetyl group linked to coenzyme Alinked to coenzyme A CHCH33

C=OC=O

SS

Coenzyme Coenzyme AA

Acetyl group

Second Second Stage of Stage of Aerobic Aerobic RespiratRespirationion

NAD+

NADH

=CoAacetyl-CoA

oxaloacetate citrate

CoA

KREBS CYCLE

H2O

malate isocitrate

FAD

FADH2

fumarate

succinate

ADP + phosphate groupATP

succinyl-CoA

O O

CoANAD+

NADH

O ONAD+

NADH

-ketoglutarate

Stepped ArtStepped Art

Fig. 7-7a, p.113

H2O

H2O

The Krebs CycleThe Krebs Cycle

Overall ProductsOverall Products

Coenzyme ACoenzyme A 2 CO2 CO22

3 NADH3 NADH FADHFADH22

ATPATP

Overall Overall ReactantsReactants

Acetyl-CoAAcetyl-CoA 3 NAD3 NAD++

FADFAD ADP and PADP and Pii

Results of the Second Results of the Second StageStage

All of the carbon molecules in All of the carbon molecules in pyruvate end up in pyruvate end up in carbon carbon dioxidedioxide

Coenzymes are Coenzymes are reducedreduced (they (they pick up electrons and hydrogen)pick up electrons and hydrogen)

One molecule of ATP is formed One molecule of ATP is formed Four-carbon oxaloacetate is Four-carbon oxaloacetate is

regeneratedregenerated

Two pyruvates cross the innermitochondrial membrane.

outer mitochondrialcompartment

NADH

NADH

FADH2

ATP

2

6

2

2

KrebsCycle

6 CO2

inner mitochondrialcompartment

Eight NADH, two FADH 2, and two ATP are the payoff from the complete break-down of two pyruvates in the second-stage reactions.

The six carbon atoms from two pyruvates diffuse out of the mitochondrion, then out of the cell, in six CO

Fig. 7-6, p.112

Coenzyme Reductions Coenzyme Reductions during First Two Stagesduring First Two Stages

GlycolysisGlycolysis 2 NADH2 NADH PreparatoryPreparatory 2 NADH2 NADH

reactionsreactions Krebs cycleKrebs cycle 2 FADH 2 FADH22 + 6 NADH + 6 NADH

TotalTotal 2 FADH 2 FADH22 + 10 + 10 NADHNADH

Section 7.4Section 7.4

Third Stage of Third Stage of Aerobic Respiration – Aerobic Respiration –

The Big Energy The Big Energy PayoffPayoff

Occurs in the mitochondriaOccurs in the mitochondria Coenzymes deliver electrons Coenzymes deliver electrons

to electron transfer chainsto electron transfer chains Electron transfer sets up HElectron transfer sets up H++

ion gradientsion gradients Flow of HFlow of H++ down gradients down gradients

powers ATP formationpowers ATP formation

Electron Transfer Electron Transfer Phosphorylation Phosphorylation

Electron Electron Transfer Transfer

PhosphorylatioPhosphorylationn

Electron transfer Electron transfer

chains are embedded chains are embedded

in inner mitochondrial in inner mitochondrial

compartmentcompartment

glucose

GLYCOLYSIS

pyruvate

KREBSCYCLE

ELECTRON TRANSFERPHOSPHORYLATION

• NADH and FADH2 give up electrons that they picked up

in earlier stages to electron transfer chain

• Electrons are transferred through the chain

• The final electron acceptor is oxygen

Creating an HCreating an H++ Gradient Gradient

NADH

OUTER COMPARTMENT

INNER COMPARTMENT

ATP FormationATP Formation

ATP

ADP+Pi

INNER COMPARTMENT

Summary of Transfersglucose

glycolysis

e–

electrontransfer

phosphorylation

2 PGAL

2 pyruvate

2 NADH

2 CO2

ATP

ATP

2 FADH2

H+

2 NADH

6 NADH

2 FADH2

2 acetyl-CoA

ATP2 KrebsCycle

4 CO2

ATP

ATP

ATP

36

ADP + Pi

H+

H+

H+

H+

H+

H+H+

H+

Importance of OxygenImportance of Oxygen

Electron transfer Electron transfer phosphorylation phosphorylation requires the requires the presence of oxygenpresence of oxygen

Oxygen withdraws spent Oxygen withdraws spent electrons from the electron electrons from the electron transfer chain, then combines transfer chain, then combines with Hwith H++ to form to form waterwater

Summary of Energy Summary of Energy HarvestHarvest

(per molecule of glucose)(per molecule of glucose) GlycolysisGlycolysis

2 ATP formed by substrate-level 2 ATP formed by substrate-level phosphorylationphosphorylation

Krebs cycleKrebs cycle and and preparatory preparatory reactionsreactions 2 ATP formed by 2 ATP formed by substrate-level substrate-level

phosphorylationphosphorylation

Electron transfer phosphorylationElectron transfer phosphorylation 32 ATP formed32 ATP formed

What are the sources of electrons What are the sources of electrons used to generate the 32 ATP in used to generate the 32 ATP in the final stage?the final stage? 4 ATP - generated using electrons 4 ATP - generated using electrons

released during glycolysis and released during glycolysis and carried by NADHcarried by NADH

28 ATP - generated using electrons 28 ATP - generated using electrons formed during second-stage formed during second-stage reactions and carried by NADH and reactions and carried by NADH and FADHFADH22

Energy Harvest from Energy Harvest from Coenzyme ReductionsCoenzyme Reductions

Energy Harvest VariesEnergy Harvest Varies

NADH formed in cytoplasm NADH formed in cytoplasm cannot enter mitochondrioncannot enter mitochondrion

It delivers electrons to It delivers electrons to mitochondrial membranemitochondrial membrane

Membrane proteins shuttle Membrane proteins shuttle electrons to NADelectrons to NAD++ or FAD inside or FAD inside mitochondrion mitochondrion

Electrons given to FAD yield less Electrons given to FAD yield less ATP than those given to NADATP than those given to NAD++

Energy Harvest VariesEnergy Harvest Varies

Liver, kidney, heart cellsLiver, kidney, heart cells Electrons from first-stage reactions are Electrons from first-stage reactions are

delivered to NADdelivered to NAD++ in mitochondria in mitochondria Total energy harvest is 38 ATPTotal energy harvest is 38 ATP

Skeletal muscle and brain cellsSkeletal muscle and brain cells Electrons from first-stage reactions are Electrons from first-stage reactions are

delivered to FAD in mitochondriadelivered to FAD in mitochondria Total energy harvest is 36 ATPTotal energy harvest is 36 ATP

Section 7.5Section 7.5

Fermentation PathwaysFermentation Pathways

Do not use oxygenDo not use oxygen

Produce less ATP than aerobic Produce less ATP than aerobic

pathwayspathways

Two types of fermentation pathwaysTwo types of fermentation pathways

AlcoholicAlcoholic fermentation fermentation

LactateLactate fermentation fermentation

Anaerobic Pathways Anaerobic Pathways

Fermentation PathwaysFermentation Pathways

Begin with glycolysisBegin with glycolysis

Do not break glucose down Do not break glucose down

completely to carbon dioxide and completely to carbon dioxide and

waterwater

Yield only the 2 ATP from glycolysisYield only the 2 ATP from glycolysis

Steps that follow glycolysis serve Steps that follow glycolysis serve

only to regenerate NADonly to regenerate NAD++

Alcoholic Fermentation

C6H12O6

ATP

ATPNADH

2 acetaldehyde

electrons, hydrogen from NADH

2 NAD+

2

2 ADP

2 pyruvate

2

4

energy output

energy input

glycolysis

ethanol formation

2 ATP net

2 ethanol

2 H2O

2 CO2

YeastsYeasts

Single-celled fungiSingle-celled fungi Carry out alcoholic fermentationCarry out alcoholic fermentation Saccharomyces cerevisiaeSaccharomyces cerevisiae

Baker’s yeastBaker’s yeastCarbon dioxide makes bread dough Carbon dioxide makes bread dough

riserise Saccharomyces ellipsoideusSaccharomyces ellipsoideus

Used to make beer and wineUsed to make beer and wine

Lactate Fermentation

C6H12O6

ATP

ATPNADH

2 lactate

electrons, hydrogen from NADH

2 NAD+

2

2 ADP

2 pyruvate

2

4

energy output

energy input

glycolysis

lactate formation

2 ATP net

Lactate FermentationLactate Fermentation

Carried out by certain bacteriaCarried out by certain bacteria Electron transfer chain is in Electron transfer chain is in

bacterial bacterial plasma membrane plasma membrane Final electron acceptor is Final electron acceptor is

compound from environment compound from environment (such as nitrate), (such as nitrate), notnot oxygen oxygen

ATP yield is lowATP yield is low

Lactate FermentationLactate Fermentation

LactobacillusLactobacillus and some other and some other bacteria produce lactatebacteria produce lactate This produces cheeses, yogurt, This produces cheeses, yogurt,

buttermilk and other dairy productsbuttermilk and other dairy products Fermenters also are used to cure Fermenters also are used to cure

meats and in picklingmeats and in pickling Sauerkraut is an exampleSauerkraut is an example Sour taste due to Sour taste due to lactic acidlactic acid (form (form

of lactate)of lactate)

Slow-twitch v. Fast-twitch Slow-twitch v. Fast-twitch musclesmuscles

Slow-twitch musclesSlow-twitch muscles make ATP only make ATP only by aerobic respiration (no by aerobic respiration (no fermentation)fermentation) Slow-twitch muscles are for Slow-twitch muscles are for light, light,

steady, prolonged steady, prolonged activityactivity Slow-twitch muscles are Slow-twitch muscles are redred because because

they have lots of myoglobin, a pigment they have lots of myoglobin, a pigment used to store oxygenused to store oxygen

They also have They also have many mitochondriamany mitochondria

Fast-twitch MusclesFast-twitch Muscles These These palepale (lighter colored) muscles (lighter colored) muscles

have have few mitochondriafew mitochondria and and no myoglobinno myoglobin Fast-twitch muscles, which are used for Fast-twitch muscles, which are used for

immediate and intense energy demands, immediate and intense energy demands, use lactate fermentation to produce ATPuse lactate fermentation to produce ATP

It works It works quicklyquickly, but not for long, but not for long Chickens have fast-twitch breast muscles Chickens have fast-twitch breast muscles

used for quick flights (white meat)used for quick flights (white meat) Ducks fly long distances – what color is Ducks fly long distances – what color is

their breast meat?their breast meat?

Alcoholic Fermentation

C6H12O6

ATP

ATPNADH

2 acetaldehyde

electrons, hydrogen from NADH

2 NAD+

2

2 ADP

2 pyruvate

2

4

energy output

energy input

glycolysis

ethanol formation

2 ATP net

2 ethanol

2 H2O

2 CO2

Lactate Fermentation

C6H12O6

ATP

ATPNADH

2 lactate

electrons, hydrogen from NADH

2 NAD+

2

2 ADP

2 pyruvate

2

4

energy output

energy input

glycolysis

lactate formation

2 ATP net

Section 7.6Section 7.6

Alternative Energy Alternative Energy Sources Sources

in the Bodyin the Body

The Fate of GlucoseThe Fate of Glucose After eating, glucose is After eating, glucose is absorbed absorbed

into the bloodinto the blood InsulinInsulin levels rise, causing greater levels rise, causing greater

uptake of glucose by cells uptake of glucose by cells GlycolysisGlycolysis will follow will follow

Excess glucose is converted into Excess glucose is converted into glycogenglycogen Glycogen is known as “animal starch,” Glycogen is known as “animal starch,”

and is the and is the main storage polysaccharide main storage polysaccharide in animalsin animals

Stored in the Stored in the musclesmuscles and the and the liverliver

Between MealsBetween Meals

When blood levels of glucose decline, When blood levels of glucose decline, pancreaspancreas

releases releases glucagonglucagon, a hormone, a hormone

Glucagon stimulates liver cells to Glucagon stimulates liver cells to convert convert

glycogen back to glucoseglycogen back to glucose and to release it to the and to release it to the

bloodblood

Glycogen levels are adequate, but can be Glycogen levels are adequate, but can be

depleted in 12 hoursdepleted in 12 hours

(Muscle cells do not release their stored (Muscle cells do not release their stored

glycogen)glycogen)

Energy ReservesEnergy Reserves

GlycogenGlycogen makes up only about makes up only about 1 percent1 percent

of the body’s energy reservesof the body’s energy reserves

ProteinsProteins make up make up 21 percent21 percent of energy of energy

reservesreserves

FatFat makes up the bulk of reserves ( makes up the bulk of reserves (78 78

percentpercent))

Energy from FatsEnergy from Fats

Most stored fats are Most stored fats are triglyceridestriglycerides in in adipose adipose

tissuetissue Triglycerides are “three-tailed” fatsTriglycerides are “three-tailed” fats

Triglycerides are broken down to Triglycerides are broken down to glycerolglycerol and and

fatty acidsfatty acids

Glycerol is converted to Glycerol is converted to PGALPGAL, an , an intermediate of intermediate of

glycolysisglycolysis

Fatty acids are broken down and converted to Fatty acids are broken down and converted to

acetyl-CoA, which enters Krebs cycleacetyl-CoA, which enters Krebs cycle

glucose

glycolysis

e–

electrontransfer

phosphorylation

2 PGAL

2 pyruvate

2 NADH

2 CO2

ATP

ATP

2 FADH2

H+

2 NADH

6 NADH

2 FADH2

2 acetyl-CoA

ATP2 KrebsCycle

4 CO2

ATP

ATP

ATP

36

ADP + Pi

H+

H+

H+

H+

H+

H+H+

H+

Energy from ProteinsEnergy from Proteins

Proteins are broken down to Proteins are broken down to amino acidsamino acids

Amino acids are broken apartAmino acids are broken apart

Amino group is removed, Amino group is removed, ammonia formsammonia forms, ,

is is converted to urea and excretedconverted to urea and excreted

Carbon backbones can enter the Krebs Carbon backbones can enter the Krebs

cycle or its preparatory reactionscycle or its preparatory reactions

Reaction SitesFOOD

fats glycogencomplex

carbohydrates proteins

simple sugars(e.g., glucose) amino acids

glucose-6-phosphate

carbon backbones

NH3

urea

ATP

(2 ATP net)

PGAL

glycolysisATP2

glycerolfatty

acids

NADH pyruvate

Acetyl-CoA

NADH CO2

KrebsCycle

NADH,FADH2

CO2

ATP

ATPATP

many ATP

fatsH+

e– + oxygen

e–

4

ATP2

Section 7.7Section 7.7

Perspective on LifePerspective on Life

When life originated, atmosphere had little When life originated, atmosphere had little

oxygenoxygen

Earliest organisms used Earliest organisms used anaerobicanaerobic pathways pathways

Later, Later, cyclic pathwaycyclic pathway (simple form) of (simple form) of

photosynthesis increased atmospheric oxygenphotosynthesis increased atmospheric oxygen

Much more efficient cells arose that used Much more efficient cells arose that used

oxygen as final acceptor in electron transferoxygen as final acceptor in electron transfer

Evolution of Metabolic Evolution of Metabolic Pathways Pathways

Processes Processes Are Are

Linked Linked

Aerobic RespirationAerobic Respiration

ReactantsReactants

Sugar Sugar

OxygenOxygen

ProductsProducts

Carbon dioxideCarbon dioxide

WaterWater

PhotosynthesisPhotosynthesis

ReactantsReactants

Carbon dioxideCarbon dioxide

WaterWater

ProductsProducts

Sugar Sugar

OxygenOxygen

Life Is System Life Is System of Prolonging Orderof Prolonging Order

Powered by energy inputs from sun, life Powered by energy inputs from sun, life

continues onward through reproductioncontinues onward through reproduction

Following instructions in DNA, energy Following instructions in DNA, energy

and materials can be organized, and materials can be organized,

generation after generationgeneration after generation

With death, molecules are released and With death, molecules are released and

may be cycled as raw material for next may be cycled as raw material for next

generation generation