CELLULAR RESPIRATIONHARVESTING CHEMICAL

ENERGY

Four Features of Four Features of EnzymesEnzymes

3) The same enzyme sometimes works 3) The same enzyme sometimes works

for both the forward and reverse for both the forward and reverse reactions, but not alwaysreactions, but not always

4) Each type of enzyme recognizes and 4) Each type of enzyme recognizes and binds to only certain substratesbinds to only certain substrates

Activation EnergyActivation Energy

For a reaction to For a reaction to occur, an energy occur, an energy barrier must be barrier must be surmountedsurmounted

Enzymes make Enzymes make the energy the energy barrier smallerbarrier smaller

activation energywithout enzyme

activation energywith enzyme

energyreleased

by thereaction

products

starting substance

Induced-Fit ModelInduced-Fit Modeltwo

substrate molecules

active sight

substratescontactingactive siteof enzyme

TRANSITIONSTATE(tightestbinding butleast stable)

endproduct

enzymeunchangedby thereaction

Substrate molecules Substrate molecules are brought togetherare brought together

Substrates are oriented Substrates are oriented in ways that favor in ways that favor reactionreaction

Active sites may Active sites may promote acid-base promote acid-base reactionsreactions

Active sites may shut Active sites may shut out waterout water

Factors Influencing Factors Influencing Enzyme ActivityEnzyme Activity

Temperature Temperature

pHpH

Salt concentrationSalt concentration

Allosteric regulatorsAllosteric regulators

Coenzymes and cofactorsCoenzymes and cofactors

Allosteric ActivationAllosteric Activation

allosteric activator

vacantallosteric binding site

active site altered, can bind substrate

active site cannot bind substrate

enzyme active site

Allosteric InhibitionAllosteric Inhibition

allosteric inhibitor

allosteric binding site vacant; active site can bind substrate

active site altered, can’t bind substrate

Feedback InhibitionFeedback Inhibition

enzyme 2 enzyme 3 enzyme 4 enzyme 5

enzyme 1

SUBSTRATE

END PRODUCT

(tryptophan)

A cellular change, caused by a specific activity, shuts down the activity that brought it about

Effect of TemperatureEffect of Temperature

Small increase in Small increase in temperature increases temperature increases molecular collisions, molecular collisions, reaction ratesreaction rates

High temperatures High temperatures disrupt bonds and disrupt bonds and destroy the shape of destroy the shape of active site active site

Effect of pHEffect of pH

Enzyme Helpers Enzyme Helpers

CofactorsCofactors CoenzymesCoenzymes

NADNAD++, NADP, NADP++, FAD, FAD Accept electrons and hydrogen ions; transfer Accept electrons and hydrogen ions; transfer

them within cellthem within cell Derived from vitaminsDerived from vitamins

Metal ionsMetal ions Ferrous iron in cytochromesFerrous iron in cytochromes

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

All energy-releasing pathways All energy-releasing pathways require characteristic starting materialsrequire characteristic starting materials yield predictable products and by-yield predictable products and by-

products products produce ATP produce ATP

Photosynthesizers get energy from Photosynthesizers get energy from the sunthe sun

Animals get energy second- or third-Animals get energy second- or third-hand from plants or other organismshand from plants or other organisms

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

ATP Is Universal ATP Is Universal Energy SourceEnergy Source

A review of how ATP drives cellular workA review of how ATP drives cellular work

Making ATPMaking ATP

Plants make ATP during Plants make ATP during

photosynthesisphotosynthesis

Cells of all organisms make ATP by Cells of all organisms make ATP by

breaking down carbohydrates, fats, breaking down carbohydrates, fats,

and proteinand protein

Redox ReactionsRedox Reactions

The loss of electrons is called The loss of electrons is called oxidationoxidation..

The addition of electrons is called The addition of electrons is called reductionreductionAAe-e- + B + B A + B A + Be-e-

Overview of Aerobic Overview of Aerobic RespirationRespiration

CC66HH12120066 + 6O + 6O22 6CO6CO22 + 6H + 6H2200 glucose oxygen glucose oxygen carbon carbon

waterwater

dioxidedioxide

In cellular respiration, glucose and other fuel In cellular respiration, glucose and other fuel molecules are oxidized, releasing energy.molecules are oxidized, releasing energy.

In the summary equation of cellular In the summary equation of cellular respiration:respiration: C C66HH1212OO66 + 6O + 6O22 -> 6CO -> 6CO22 + 6H + 6H22OO

Glucose is oxidized, oxygen is reduced, and Glucose is oxidized, oxygen is reduced, and electrons loose potential energy.electrons loose potential energy.

Cellular respiration does not oxidize glucose Cellular respiration does not oxidize glucose in a single step that transfers all the in a single step that transfers all the hydrogen in the fuel to oxygen at one time.hydrogen in the fuel to oxygen at one time.

Rather, glucose and other fuels are broken Rather, glucose and other fuels are broken down gradually in a series of steps, each down gradually in a series of steps, each catalyzed by a specific enzymecatalyzed by a specific enzyme

Electrons “fall” from organic molecules to Electrons “fall” from organic molecules to oxygen during cellular respirationoxygen during cellular respiration

Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

An overview of cellular respiration (Layer 1)An overview of cellular respiration (Layer 1)

An overview of cellular respiration (Layer 2)An overview of cellular respiration (Layer 2)

An overview of cellular respiration (Layer 3)An overview of cellular respiration (Layer 3)

Glycolysis Occurs Glycolysis Occurs in Two Stages in Two Stages

Energy-requiring stepsEnergy-requiring steps ATP energy activates glucose and its six-ATP energy activates glucose and its six-

carbon derivativescarbon derivatives

Energy-releasing stepsEnergy-releasing steps The products of the first part are split into The products of the first part are split into

three-carbon pyruvate moleculesthree-carbon pyruvate molecules

ATP and NADH formATP and NADH form

Energy-Requiring Steps Energy-Requiring Steps

ATP

ATP

glucose

glucose-6-phosphate

fructose-6-phosphate

fructose-1,6-bisphosphate

2 ATP investedADP

ADP

P

P

P

Energy-Energy-ReleasinReleasing Stepsg Steps

ATP

PGAL PGAL

ATP

NADH NADH

ATP ATP

2 ATP invested

2 ATP invested

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

substrate-level phosphorylation

substrate-level phosphorylation

H2O H2O

ADP ADP

Net Energy Yield Net Energy Yield from Glycolysisfrom Glycolysis

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

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

Net yield is 2 ATP and 2 NADHNet yield is 2 ATP and 2 NADH

Occur in the Occur in the mitochondriamitochondria

Pyruvate is Pyruvate is broken down to broken down to carbon dioxidecarbon dioxide

More ATP is More ATP is formedformed

More coenzymes More coenzymes are reduced are reduced

Second-Stage Second-Stage

ReactionsReactions

oxaloacetate

malate

citrate

isocitrate

-ketogluterate

fumarate

succinate

CoA

succinyl–CoA

ATP

NADH

NADH

NADH

NADH

FADH2

NAD+

NAD+

FAD NAD+ CoA

CoA

H2O

H2O

H2O

ADP + phosphate group (from GTP)

KREBS CYCLE

PREPARATORY STEPS

pyruvate

NAD+

CoAAcetyl–CoA

coenzyme A (CoA)

(CO2)

Two Parts of Second Two Parts of Second Stage Stage

Preparatory reactionsPreparatory reactions Pyruvate is oxidized into two-carbon Pyruvate is oxidized into two-carbon

acetyl units and carbon dioxideacetyl units and carbon dioxide NADNAD++ is reduced is reduced

Krebs cycleKrebs cycle The acetyl units are oxidized to carbon The acetyl units are oxidized to carbon

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

Preparatory ReactionsPreparatory Reactions

What is Acetyl-CoA?What is Acetyl-CoA?

A two-carbon acetyl group linked to A two-carbon acetyl group linked to coenzyme Acoenzyme A

CHCH33

C=OC=O

Coenzyme ACoenzyme A

Acetyl group

The Krebs CycleThe Krebs Cycle

Overall ProductsOverall Products

Coenzyme ACoenzyme A 2 CO2 CO22

3 NADH3 NADH FADHFADH22

ATPATP

Overall ReactantsOverall Reactants

Acetyl-CoAAcetyl-CoA 3 NAD3 NAD++

FADFAD ADP and PADP and Pii

A summary of the Krebs cycleA summary of the Krebs cycle

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 carbon dioxidepyruvate end up in carbon dioxide

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

Coenzyme Reductions Coenzyme Reductions During First Two StagesDuring First Two Stages

GlycolysisGlycolysis 2 NADH2 NADH PreparatoryPreparatory

reactionsreactions 2 NADH2 NADH Krebs cycleKrebs cycle 2 FADH 2 FADH22 + 6 NADH + 6 NADH

TotalTotal 2 FADH 2 FADH22 + 10 NADH + 10 NADH

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

electron transport systemselectron transport systems Electron transport sets up HElectron transport sets up H++ ion ion

gradientsgradients Flow of HFlow of H++ down gradients powers down gradients powers

ATP formationATP formation

Electron Transport Electron Transport Phosphorylation Phosphorylation

Electron TransportElectron Transport

Electron transport systems are embedded Electron transport systems are embedded

in inner mitochondrial compartmentin inner mitochondrial compartment

NADH and FADHNADH and FADH2 2 give up electrons that give up electrons that

they picked up in earlier stages to electron they picked up in earlier stages to electron

transport systemtransport system Electrons are transported through the Electrons are transported through the

systemsystem The final electron acceptor is oxygenThe final electron acceptor is oxygen

Creating an HCreating an H++ Gradient Gradient

NADH

OUTER COMPARTMENT

INNER COMPARTMENT

Making ATP: Making ATP: Chemiosmotic ModelChemiosmotic Model

ATP

ADP+Pi

INNER COMPARTMENT

Importance of OxygenImportance of Oxygen

Electron transport phosphorylation Electron transport phosphorylation requires the presence of oxygenrequires the presence of oxygen

Oxygen withdraws spent electrons Oxygen withdraws spent electrons from the electron transport system, from the electron transport system, then combines with Hthen combines with H++ to form water to form water

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 cycle and preparatory reactionsKrebs cycle and preparatory reactions 2 ATP formed by substrate-level 2 ATP formed by substrate-level

phosphorylationphosphorylation

Electron transport phosphorylationElectron transport 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 the used to generate the 32 ATP in the final stage?final stage? 4 ATP - generated using electrons 4 ATP - generated using electrons

released during glycolysis and carried released during glycolysis and carried by NADHby NADH

28 ATP - generated using electrons 28 ATP - generated using electrons formed during second-stage reactions formed during second-stage reactions and carried by NADH and FADHand carried by NADH and FADH22

Energy Harvest from Energy Harvest from Coenzyme ReductionsCoenzyme Reductions

Energy Harvest VariesEnergy Harvest Varies

NADH formed in cytoplasm cannot NADH formed in cytoplasm cannot enter mitochondrionenter mitochondrion

It delivers electrons to mitochondrial It delivers electrons to mitochondrial membranemembrane

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

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

686 kcal of energy are released 686 kcal of energy are released

7.5 kcal are conserved in each ATP7.5 kcal are conserved in each ATP

When 36 ATP form, 270 kcal (36 X 7.5) are When 36 ATP form, 270 kcal (36 X 7.5) are

captured in ATPcaptured in ATP

Efficiency is 270 / 686 X 100 = 39 percent Efficiency is 270 / 686 X 100 = 39 percent

Most energy is lost as heatMost energy is lost as heat

Efficiency ofEfficiency of Aerobic Respiration Aerobic Respiration

Do not use oxygenDo not use oxygen

Produce less ATP than aerobic Produce less ATP than aerobic

pathwayspathways

Two typesTwo types

Fermentation pathwaysFermentation pathways

Anaerobic electron transportAnaerobic electron transport

Anaerobic Pathways Anaerobic Pathways

Fermentation PathwaysFermentation Pathways

Begin with glycolysisBegin with glycolysis

Do not break glucose down completely to Do not break glucose down completely to

carbon dioxide and watercarbon dioxide and water

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

Steps that follow glycolysis serve only to Steps that follow glycolysis serve only to

regenerate NADregenerate NAD++

Lactate FermentationLactate 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

Alcoholic Alcoholic FermentatiFermentati

onon

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 yeast Carbon dioxide makes bread dough rise Carbon dioxide makes bread dough rise

Saccharomyces ellipsoideusSaccharomyces ellipsoideus Used to make beer and wineUsed to make beer and wine

Anaerobic Electron Anaerobic Electron TransportTransport

Carried out by certain bacteriaCarried out by certain bacteria Electron transport system is in bacterial Electron transport system is in bacterial

plasma membrane plasma membrane Final electron acceptor is compound from Final electron acceptor is compound from

environment (such as nitrate), NOT environment (such as nitrate), NOT oxygenoxygen

ATP yield is almost as good as from ATP yield is almost as good as from aerobic respirationaerobic respiration

Energy from ProteinsEnergy from Proteins

Proteins are broken down to amino acidsProteins are broken down to amino acids

Amino acids are broken apartAmino acids are broken apart

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

is converted to urea and excretedis converted 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

Energy from FatsEnergy from Fats

Most stored fats are triglyceridesMost stored fats are triglycerides

Triglycerides are broken down to glycerol Triglycerides are broken down to glycerol

and fatty acids and fatty acids

Glycerol is converted to PGAL, an Glycerol is converted to PGAL, an

intermediate of glycolysisintermediate of glycolysis

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

to acetyl-CoA, which enters Krebs cycleto acetyl-CoA, which enters Krebs cycle

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

oxygenoxygen

Earliest organisms used anaerobic pathwaysEarliest organisms used anaerobic pathways

Later, noncyclic pathway of photosynthesis Later, noncyclic pathway of photosynthesis

increased atmospheric oxygenincreased atmospheric oxygen

Cells arose that used oxygen as final Cells arose that used oxygen as final

acceptor in electron transportacceptor in electron transport

Evolution of Metabolic Evolution of Metabolic Pathways Pathways