Chapter 6Chapter 6

How Cells Harvest Chemical EnergyHow Cells Harvest Chemical Energy

BREATHING VERSUS RESPIRATIONBREATHING VERSUS RESPIRATION BREATHINGBREATHING::

Alternation of inhalation and exhalation.Alternation of inhalation and exhalation. Exchange of gases in which organisms obtain Exchange of gases in which organisms obtain oxygenoxygen

from the air (or water) and release from the air (or water) and release carbon dioxide.carbon dioxide. Exchange occurs in Exchange occurs in lungs lungs (or gills)(or gills)..

CELLULAR RESPIRATION: CELLULAR RESPIRATION: Harvesting of energy from food molecules by cells. Harvesting of energy from food molecules by cells. AerobicAerobic process (requires oxygen). process (requires oxygen). Occurs inside Occurs inside cells cells (cytoplasm and mitochondria)(cytoplasm and mitochondria)..

““Respiration” comes from Latin word for breathing.Respiration” comes from Latin word for breathing.

Breathing and cellular respiration are closely Breathing and cellular respiration are closely

related, but related, but notnot the same processes. the same processes.

Breathing versus Cellular Respiration

CELLULAR RESPIRATION BANKS ATPCELLULAR RESPIRATION BANKS ATP

REACTIONREACTION::CC66HH1212OO66 + 6O + 6O22 ----> 6CO ----> 6CO22 + 6H + 6H22O + O + ENERGYENERGY

(Glucose) (Oxygen) (Carbon dioxide) (Water)(Glucose) (Oxygen) (Carbon dioxide) (Water)

What happens to the energy in glucose or other What happens to the energy in glucose or other food molecules?food molecules? Only about 40% of energy is turned into ATPOnly about 40% of energy is turned into ATP The rest is lost as metabolic heat.The rest is lost as metabolic heat. One One ATPATP molecule has about molecule has about 1%1% of the of the

chemical energy found in glucose.chemical energy found in glucose.

ENERGY CONVERSIONS ARE INEFFICIENTSecond Law of Thermodynamics

By Comparison Living Organisms Are Efficient

CATABOLISMCATABOLISM::

Process of splitting larger molecules to smaller Process of splitting larger molecules to smaller ones. Catabolic reactions are exergonic and ones. Catabolic reactions are exergonic and release free energy.release free energy.

THREE MAJOR CATABOLIC PATHWAYS THREE MAJOR CATABOLIC PATHWAYS IN LIVING ORGANISMSIN LIVING ORGANISMS

A. A. Aerobic (Cellular) respirationAerobic (Cellular) respiration

B.B. Anaerobic respirationAnaerobic respiration

C.C. FermentationFermentation

MAJOR CATABOLIC PATHWAYSMAJOR CATABOLIC PATHWAYS

A. A. Aerobic (Cellular) respirationAerobic (Cellular) respiration:: Requires Requires oxygenoxygen.. Most commonly used catabolic pathway.Most commonly used catabolic pathway. Over 30 reactions. Used to extract energy from Over 30 reactions. Used to extract energy from

glucose molecules.glucose molecules. Final electron acceptor:Final electron acceptor: OxygenOxygen.. Most Most efficientefficient: 40% of glucose energy is : 40% of glucose energy is

converted into ATP.converted into ATP.

REACTIONREACTION::CC66HH1212OO66 + 6O + 6O22 ---> 6CO ---> 6CO22 + 6H + 6H22O + O + ENERGYENERGY

GlucoseGlucose OxygenOxygen Carbon dioxide Water Carbon dioxide Water

THREE MAJOR CATABOLIC THREE MAJOR CATABOLIC PATHWAYSPATHWAYS

B. B. Anaerobic respirationAnaerobic respiration:: Does Does notnot require require oxygenoxygen.. Used by bacteria that live in environments Used by bacteria that live in environments

without oxygen.without oxygen. Final electron acceptor:Final electron acceptor: InorganicInorganic molecule molecule.. Very Very inefficientinefficient: Only 2% of glucose energy is : Only 2% of glucose energy is

converted into ATP.converted into ATP. Final productsFinal products: Carbon dioxide, water, and : Carbon dioxide, water, and

other other inorganicinorganic compounds. compounds.

THREE MAJOR CATABOLIC PATHWAYSTHREE MAJOR CATABOLIC PATHWAYS

C. C. FermentationFermentation:: Does Does notnot require require oxygenoxygen.. Used by yeast, bacteria, and other cells when Used by yeast, bacteria, and other cells when

oxygen is not available.oxygen is not available. Final electron acceptor:Final electron acceptor: OrganicOrganic molecule.molecule. Very Very inefficientinefficient: Only 2% of glucose energy is : Only 2% of glucose energy is

converted into ATP.converted into ATP. Products depend on type of fermentation:Products depend on type of fermentation:

Lactic acid fermentationLactic acid fermentation: Used to make cheese and : Used to make cheese and yogurt. Carried out by muscle cells if oxygen is low.yogurt. Carried out by muscle cells if oxygen is low.

Alcoholic fermentationAlcoholic fermentation: Used to make alcoholic : Used to make alcoholic beverages. Produces alcohol and carbon dioxide. beverages. Produces alcohol and carbon dioxide.

II. Hydrogen carriers shuttle electrons in II. Hydrogen carriers shuttle electrons in REDOX reactionsREDOX reactionsOxidationOxidation: : Partial or complete Partial or complete lossloss of electrons or H atoms. of electrons or H atoms. When a molecule is oxidized it When a molecule is oxidized it losesloses energy. energy.ReductionReduction: : Partial or complete Partial or complete gaingain of of electrons or H atoms. electrons or H atoms. When a molecule is reduced it When a molecule is reduced it gainsgains energy. energy. REDOX ReactionsREDOX Reactions: : Reactions in which Reactions in which bothboth oxidation and reduction oxidation and reduction

occur. occur. Characteristic of many cell processes, including Characteristic of many cell processes, including

aerobic respiration and photosynthesis.aerobic respiration and photosynthesis.

Cellullar Respiration is a Redox Process: Involves Both Oxidation and Reduction

Glucose is oxidized to carbon dioxide.Oxygen is reduced to water.

III. Redox reactions in living organismsIII. Redox reactions in living organisms

Cellular RespirationCellular Respiration:: MacromoleculesMacromolecules oxidizedoxidized to release to release energy (686 kcal/mole) which is used to synthesize ATPenergy (686 kcal/mole) which is used to synthesize ATP

CC66HH1212OO66 + 6O + 6O22 ---> 6CO ---> 6CO22 + 6H + 6H22O + O + ENERGYENERGY

Glucose Glucose Oxygen Oxygen (oxidized) (reduced)(oxidized) (reduced)

PhotosynthesisPhotosynthesis:: COCO22 is is reducedreduced ; requires energy to drive ; requires energy to drive

the reaction forwardthe reaction forward

6CO6CO22 + 6H + 6H22O + O + ENERGYENERGY ---> C ---> C66HH1212OO66 + 6O + 6O22

Carbon Carbon WaterWater (reduced) (oxidized) (reduced) (oxidized)DioxideDioxide High EnergyHigh Energy

IV. Hydrogen carriers shuttle electrons in redox IV. Hydrogen carriers shuttle electrons in redox reactionsreactions

1. Dehydrogenase:1. Dehydrogenase: Removes hydrogen atoms (with their Removes hydrogen atoms (with their

electrons) from organic molecules and transfers them electrons) from organic molecules and transfers them

to an electron carrier. to an electron carrier.

2. Electron Carrier Molecules:2. Electron Carrier Molecules: NADNAD++: (Nicotinamide adenine dinucleotide): (Nicotinamide adenine dinucleotide)

Coenzyme that accepts and Coenzyme that accepts and transfers most H and the transfers most H and the high energy electronshigh energy electrons released by redox reactions released by redox reactions

ReductionReduction

NADNAD++ + 2H ------------> NADH + H + 2H ------------> NADH + H++

(2H(2H++ & 2e & 2e--))

FADHFADH22 (Flavin adenine dinucleotide)(Flavin adenine dinucleotide): Secondary H : Secondary H

carrier, related to NADH.carrier, related to NADH.

Dehydrogenase and Hydrogen Carriers Shuttle Electrons in Redox Reactions

IV. Electrons “fall” from Hydrogen Carriers to IV. Electrons “fall” from Hydrogen Carriers to Oxygen in the Electron Transport ChainOxygen in the Electron Transport Chain NADH:NADH: (Nicotinamide andenine dinucleotide) (Nicotinamide andenine dinucleotide) : :

Delivers Delivers H and the high energy electronsH and the high energy electrons released by released by redox reactions to electron carrier molecule of chain.redox reactions to electron carrier molecule of chain.

Electron transport chainElectron transport chain:: Proteins on inner Proteins on inner mitochondrial membrane that accept H and use high mitochondrial membrane that accept H and use high energy electrons to produce ATP.energy electrons to produce ATP.

As Electrons “Fall” From Hydrogen Carriers to Oxygen, Energy is Released

Two different means of ATP production:Two different means of ATP production:

1. 1. Substrate-level phosphorylationSubstrate-level phosphorylation: :

Generates a small amount of ATP during cellular Generates a small amount of ATP during cellular

respiration.respiration.

Simple process, does not require membranes.Simple process, does not require membranes.

Phosphate group is Phosphate group is directlydirectly transferred from an transferred from an

organic molecule to ADP to make ATP.organic molecule to ADP to make ATP.

Occurs in first two stages of aerobic respiration:Occurs in first two stages of aerobic respiration: GlycolysisGlycolysis

Kreb’s cycleKreb’s cycle

Two different means of ATP production:Two different means of ATP production:

2. 2. Oxidative phosphorylation (Chemiosmosis)Oxidative phosphorylation (Chemiosmosis)::

Generates most of ATP made during cellular respirationGenerates most of ATP made during cellular respiration

Complex process, requires Complex process, requires mitochondrialmitochondrial membranesmembranes..

Energy released from exergonic reactions of electron Energy released from exergonic reactions of electron

transport is used to pump Htransport is used to pump H++ ions across membrane, ions across membrane,

creating a concentration gradient (potential energy).creating a concentration gradient (potential energy).

ChemiosmosisChemiosmosis: ATP is made by : ATP is made by ATP synthaseATP synthase on on

mitochondrial membranes, as Hmitochondrial membranes, as H++ flow down flow down

concentration gradient.concentration gradient.

Occurs in last stage of aerobic respiration.Occurs in last stage of aerobic respiration.

RequiresRequires the presence of the presence of OXYGENOXYGEN

Two Mechanisms of ATP Synthesis: Oxidative and Substrate Level Phosphorylation

V. Three Stages of Cellular RespirationV. Three Stages of Cellular Respiration

A. A. GlycolysisGlycolysis

B. B. Kreb’s CycleKreb’s Cycle

C. C. Electron Transport Chain & ChemiosmosisElectron Transport Chain & Chemiosmosis

Three Stages of Aerobic Respiration

A. A. Glycolysis: “Splitting sugar”Glycolysis: “Splitting sugar” Occurs in the Occurs in the cytoplasmcytoplasm of the cell of the cell Does not require oxygenDoes not require oxygen 9 chemical reactions9 chemical reactions Net result:Net result: Glucose molecule (6 carbons each) is split Glucose molecule (6 carbons each) is split

into two into two pyruvic acid molecules pyruvic acid molecules of 3 carbons each.of 3 carbons each. Yield per glucose molecule:Yield per glucose molecule:

2 ATP ( Substrate-level phosphorylation)2 ATP ( Substrate-level phosphorylation)

2 NADH + 2 H2 NADH + 2 H++

(2 ATP are “invested” to get 4 ATP back)(2 ATP are “invested” to get 4 ATP back) Pyruvic acid diffuses into mitochondrial matrix where Pyruvic acid diffuses into mitochondrial matrix where

all subsequent reactions take place.all subsequent reactions take place.

Glycolysis: “Splitting” of Glucose into Two Molecules of Pyruvic Acid

Conversion of Pyruvate to Acetyl CoAConversion of Pyruvate to Acetyl CoA

BeforeBefore entering the next stage, entering the next stage, pyruvic acidpyruvic acid (3C)(3C) must must be converted tobe converted to Acetyl CoAAcetyl CoA (2 C). (2 C).

A carbon atom is lost as COA carbon atom is lost as CO22..

Yield per glucose molecule:Yield per glucose molecule: 2 NADH + 2 H2 NADH + 2 H++

B. B. Kreb’s CycleKreb’s Cycle

Occurs in the Occurs in the matrixmatrix of the mitochondrion of the mitochondrion A A cycle of 8 reactionscycle of 8 reactions

Reaction 1Reaction 1: Acetyl CoA (2C) joins with 4C molecule : Acetyl CoA (2C) joins with 4C molecule (oxaloacetic acid) to produce citric acid (6C).(oxaloacetic acid) to produce citric acid (6C).

Reactions 2 & 3Reactions 2 & 3: Citric acid loses 2C atoms as CO: Citric acid loses 2C atoms as CO22.. Reactions 4 & 5Reactions 4 & 5: REDOX reactions produce NADH : REDOX reactions produce NADH

and FADHand FADH22.. Reactions 6-8:Reactions 6-8: Oxaloacetic acid is regenerated. Oxaloacetic acid is regenerated.

Kreb’s Cycle: Two Carbons In, Two Carbons Out

Details of Kreb’s Cycle

B. B. Kreb’s CycleKreb’s Cycle

Carbons are released asCarbons are released as CO CO22

Yield per glucose molecule:Yield per glucose molecule:

2 ATP (substrate-level 2 ATP (substrate-level phosphorylation)phosphorylation)

6 NADH + 6 H6 NADH + 6 H++

2 FADH2 FADH2 2

C. C. Electron Transport Chain & ChemiosmosisElectron Transport Chain & Chemiosmosis Most ATP is produced at this stageMost ATP is produced at this stage Occurs on inner mitochondrial membraneOccurs on inner mitochondrial membrane Electrons fromElectrons from NADH and FADHNADH and FADH22 are transferred to are transferred to

electron acceptors, which produces aelectron acceptors, which produces a proton gradientproton gradient Proton gradientProton gradient used to drive synthesis of ATP.used to drive synthesis of ATP. ChemiosmosisChemiosmosis: ATP synthase allows H: ATP synthase allows H++ to flow across to flow across

inner mitochondrial membrane down concentration inner mitochondrial membrane down concentration gradient, which produces ATP.gradient, which produces ATP.

Ultimate acceptor of HUltimate acceptor of H++ and electrons is and electrons is OXYGENOXYGEN, , producing producing waterwater..

Electron Transport & Chemiosmosis: GeneratesMost ATP Produced During Cellular Respiration

NOTENOTE:: The electron transport chain ONLY The electron transport chain ONLY

works when OXYGEN is available at the end works when OXYGEN is available at the end

of the chain to accept the electrons and Hof the chain to accept the electrons and H++ to to

form water.form water.

C. C. Electron Transport Chain & ChemiosmosisElectron Transport Chain & Chemiosmosis

Yield of ATP through Chemiosmosis:Yield of ATP through Chemiosmosis: Each NADH produces 3 ATPEach NADH produces 3 ATP Each FAHD2 produces 2 ATPEach FAHD2 produces 2 ATP

2 NADH 2 NADH (Glycolysis) x 3 ATP (Glycolysis) x 3 ATP = = 6 ATP6 ATP

2 NADH 2 NADH (Acetyl CoA) x 3 ATP (Acetyl CoA) x 3 ATP = = 6 ATP6 ATP

6 NADH 6 NADH (Kreb’s cycle) x 3 ATP(Kreb’s cycle) x 3 ATP = 18 ATP= 18 ATP

2 FADH2 FADH22 (Kreb’s cycle) x 2 ATP (Kreb’s cycle) x 2 ATP = = 4 ATP4 ATP

________________________________

32 - 34 ATP 32 - 34 ATP

These ATPs are made by These ATPs are made by oxidativeoxidative phosphorylation phosphorylation

oror chemiosmosis.chemiosmosis.

VIII. Total Energy from cellular respirationVIII. Total Energy from cellular respirationSubstrateSubstrate OxidativeOxidative

ProcessProcess PhosphorylPhosphoryl e-Carriere-Carrier Phosphoryl PhosphorylTOTALTOTAL

GlycolysisGlycolysis 2 ATP2 ATP 2 NADH2 NADH ---> ---> 4 - 6 ATP4 - 6 ATP 6-8 ATP6-8 ATP

Acetyl CoAAcetyl CoA 2 NADH2 NADH ---> ---> 6 ATP6 ATP 6 6 ATPATP

FormationFormation

Kreb’sKreb’s 2 ATP2 ATP 6 NADH6 NADH ---> ---> 18 ATP18 ATP

2 FADH2 FADH22 --->---> 6 ATP6 ATP

24 ATP24 ATP

____________________

Total yield per glucose :Total yield per glucose : 36-38 36-38 ATPATP

Many poisons interrupt cellular respirationMany poisons interrupt cellular respiration Electron transport chain blockers:Electron transport chain blockers:

Rotenone: PesticideRotenone: Pesticide

CyanideCyanide

Carbon monoxideCarbon monoxide

ATP synthase inhibitorsATP synthase inhibitors Oligomycin: Antifungal drug. Used on skin.Oligomycin: Antifungal drug. Used on skin.

UncouplersUncouplers: Make mitochondrial membrane leaky : Make mitochondrial membrane leaky

to H+ ions. Abolishes H+ gradient, can’t make to H+ ions. Abolishes H+ gradient, can’t make

ATP through chemiosmosis.ATP through chemiosmosis. Dinitrophenol (DNP): Used in 1940s as weight loss Dinitrophenol (DNP): Used in 1940s as weight loss

drug.drug.

Effects of Various Poisons on the Electron Effects of Various Poisons on the Electron Transport ChainTransport Chain

FERMENTATION OCCURS WHEN OXYGEN FERMENTATION OCCURS WHEN OXYGEN IS NOT AVAILABLEIS NOT AVAILABLE

Yeasts normally use aerobic respiration to Yeasts normally use aerobic respiration to process food.process food.

If oxygen is not available, they use fermentation, If oxygen is not available, they use fermentation, which is less efficient.which is less efficient.

Types of fermentation:Types of fermentation:

Alcoholic fermentationAlcoholic fermentation

Glucose ----> 2 pyruvate ----> Glucose ----> 2 pyruvate ----> 2 Ethanol + 2 CO2 Ethanol + 2 CO22

Lactic acid fermentationLactic acid fermentation

Glucose ----> 2 pyruvate ----> Glucose ----> 2 pyruvate ----> 2 Lactic acids2 Lactic acids

Fermentation Occurs When Oxygen is Unavailable

Alcoholic and Lactic Acid Fermentation: An Alternative to Aerobic Respiration

ORGANISMS CAN BE CLASSIFIED BASED ORGANISMS CAN BE CLASSIFIED BASED

ON THEIR OXYGEN REQUIREMENTSON THEIR OXYGEN REQUIREMENTS

Strict aerobesStrict aerobes:: Require oxygen for survival. Require oxygen for survival.

All large organisms are aerobes.All large organisms are aerobes. Examples: Humans, dogs, insects.Examples: Humans, dogs, insects.

Strict anaerobesStrict anaerobes:: Grow only in the absence of Grow only in the absence of

oxygen. Are poisoned by oxygen.oxygen. Are poisoned by oxygen. Examples: Bacteria that live in soil and animal Examples: Bacteria that live in soil and animal

intestines.intestines.

Facultative anaerobesFacultative anaerobes:: Grow with/without Grow with/without

oxygen. Grow better with oxygen.oxygen. Grow better with oxygen. Examples: Yeast and many bacteria.Examples: Yeast and many bacteria.

All Food Molecules are Fed into The Catabolic Pathway of Aerobic Respiration