Cellular Respiration: Harvesting Chemical Energy

Cellular Respiration:Cellular Respiration:Harvesting Chemical EnergyHarvesting Chemical Energy

AP BiologyAP Biology

Ms. HautMs. Haut

Energy FlowEnergy FlowEnergy flows into an Energy flows into an ecosystem as sunlight ecosystem as sunlight and leaves as heatand leaves as heatPhotosynthesis Photosynthesis generates oxygen and generates oxygen and organic molecules, organic molecules, which are used in which are used in cellular respirationcellular respiration

Cells use chemical Cells use chemical energy stored in organic energy stored in organic molecules to regenerate molecules to regenerate ATP, which powers workATP, which powers work

Catabolic Pathways and Catabolic Pathways and Production of ATPProduction of ATP

The breakdown of organic molecules is The breakdown of organic molecules is exergonicexergonic

FermentationFermentation is a partial degradation of sugars is a partial degradation of sugars that occurs without oxygenthat occurs without oxygen

Cellular respirationCellular respiration consumes oxygen and consumes oxygen and organic molecules and yields ATPorganic molecules and yields ATP

Although carbohydrates, fats, and proteins are Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose:cellular respiration with the sugar glucose:

CC66HH1212OO66 + 6O + 6O22 6CO 6CO22 + 6H + 6H22O + Energy (ATP + heat)O + Energy (ATP + heat)

Cellular RespirationCellular Respiration

ATP-producing catabolic process in ATP-producing catabolic process in which the ultimate electron acceptor which the ultimate electron acceptor is an inorganic compound, Oxygenis an inorganic compound, Oxygen

Most efficient catabolic pathwayMost efficient catabolic pathwayIs an exergonic process Is an exergonic process ((ΔΔG = -686kcal/mol)G = -686kcal/mol)

CC66HH1212OO66 + 6O + 6O22 6CO 6CO22 + 6H + 6H22O + Energy (ATP + Heat)O + Energy (ATP + Heat)

Oxidation

Reduction

Electrons “fall” from Organic Molecules to Electrons “fall” from Organic Molecules to Oxygen during Cellular Respiration Oxygen during Cellular Respiration

The Stages of Cellular The Stages of Cellular Respiration: Respiration: A PreviewA Preview

Cellular respiration has three stages:Cellular respiration has three stages:– GlycolysisGlycolysis (breaks down glucose into two (breaks down glucose into two

molecules of pyruvate)molecules of pyruvate)– The The Krebs Cycle (citric acid cycle)Krebs Cycle (citric acid cycle) (completes (completes

the breakdown of glucose)the breakdown of glucose)– Oxidative phosphorylationOxidative phosphorylation (accounts for most (accounts for most

of the ATP synthesis)of the ATP synthesis)

The process that generates most of the ATP The process that generates most of the ATP is called oxidative phosphorylation because is called oxidative phosphorylation because it is powered by redox reactionsit is powered by redox reactions

GlycolysisGlycolysisCatabolic pathwayCatabolic pathway

Occurs in the Occurs in the cytosolcytosol

Partially oxidizes Partially oxidizes glucose (6C) into glucose (6C) into two pyruvate (3C) two pyruvate (3C) moleculesmolecules

Mitochondrion

Glycolysis

PyruvateGlucose

Cytosol

ATP

Substrate-levelphosphorylation

Krebs CycleKrebs CycleCatabolic pathwayCatabolic pathway

Occurs in Occurs in mitochondrial mitochondrial matrixmatrix

Completes glucose Completes glucose oxidation by oxidation by breaking down a breaking down a acetyl-CoA into COacetyl-CoA into CO22

Mitochondrion

Glycolysis

PyruvateGlucose

Cytosol

ATP


ATP


Citricacidcycle

Glycolysis and Krebs CycleGlycolysis and Krebs Cycle

Together produce:Together produce:

Small amount of Small amount of ATPATP by substrate- by substrate-level phosphorylationlevel phosphorylation

NADHNADH by transferring electrons from by transferring electrons from substrate to NAD+substrate to NAD+

Krebs Cycle also produces Krebs Cycle also produces FADHFADH22 by by transferring electrons to FAD+transferring electrons to FAD+

Electron Transport ChainElectron Transport ChainLocated near inner Located near inner membrane of membrane of mitochondrionmitochondrion

Accepts energized Accepts energized electrons from reduced electrons from reduced coenzymes (NADH and coenzymes (NADH and FADHFADH22) that are ) that are harvested during harvested during glycolysis and Krebs glycolysis and Krebs CycleCycle– Oxygen pulls electrons Oxygen pulls electrons

down ETC to a lower down ETC to a lower energy stateenergy state

Mitochondrion

Glycolysis

PyruvateGlucose

Cytosol

ATP


ATP


Citricacidcycle

ATP

Oxidativephosphorylation

Oxidativephosphorylation:electron transport

andchemiosmosis

Electronscarried

via NADH

Electrons carriedvia NADH and

FADH2

Oxidative PhosphorylationOxidative PhosphorylationAccounts for almost 90% of the ATP Accounts for almost 90% of the ATP generated by cellular respirationgenerated by cellular respirationEnergy released at each step of the ETC is Energy released at each step of the ETC is stored in a form the mitochondrion can stored in a form the mitochondrion can use to make ATPuse to make ATP– Powered by redox reactions that transfer Powered by redox reactions that transfer

electrons from food to oxygenelectrons from food to oxygen

Small amount of ATP is produced directly Small amount of ATP is produced directly by the enzymatic transfer of phosphate by the enzymatic transfer of phosphate from an intermediate substrate in from an intermediate substrate in catabolism to ADP (catabolism to ADP (substrate-level substrate-level phosphorylationphosphorylation))

GlycolysisGlycolysisGlycolysis (“splitting Glycolysis (“splitting of sugar”) breaks of sugar”) breaks down glucose into down glucose into two molecules of two molecules of pyruvatepyruvate

Two major phases:Two major phases:– Energy investment Energy investment

phasephase– Energy payoff Energy payoff

phasephase

GlycolysisGlycolysis




Conversion of Pyruvate to Acetyl CoA:Pyruvate Oxidation

Krebs CycleKrebs Cycle

http://library.thinkquest.org/C004535/media/kreb_cycle.gif

LE 9-12_1LE 9-12_1

ATP ATP ATP

Glycolysis Oxidationphosphorylation

Citricacidcycle

Citricacidcycle

Citrate

Isocitrate

Oxaloacetate

Acetyl CoA

H2O

LE 9-12_2LE 9-12_2

ATP ATP ATP


Citricacidcycle

Citricacidcycle

Citrate

Isocitrate

Oxaloacetate

Acetyl CoA

H2O

CO2

NAD+

NADH

+ H+

-Ketoglutarate

CO2NAD+

NADH

+ H+SuccinylCoA

LE 9-12_3LE 9-12_3

ATP ATP ATP


Citricacidcycle

Citricacidcycle

Citrate

Isocitrate

Oxaloacetate

Acetyl CoA

H2O

CO2

NAD+

NADH

+ H+

-Ketoglutarate

CO2NAD+

NADH

+ H+SuccinylCoA

Succinate

GTP GDP

ADP

ATP

FAD

FADH2

P i

Fumarate

LE 9-12_4LE 9-12_4

ATP ATP ATP


Citricacidcycle

Citricacidcycle

Citrate

Isocitrate

Oxaloacetate

Acetyl CoA

H2O

CO2

NAD+

NADH

+ H+

-Ketoglutarate

CO2NAD+

NADH

+ H+SuccinylCoA

Succinate

GTP GDP

ADP

ATP

FAD

FADH2

P i

Fumarate

H2O

Malate

NAD+

NADH

+ H+

Net: 2 molecules of pyruvate 8 NADH 2 FADH2

2 ATP

During oxidative phosphorylation, During oxidative phosphorylation, chemiosmosis couples electron transport to chemiosmosis couples electron transport to

ATP synthesisATP synthesis

• Following glycolysis and the citric acid cycle, Following glycolysis and the citric acid cycle, NADH and FADHNADH and FADH22 account for most of the account for most of the energy extracted from foodenergy extracted from food

• These two electron carriers donate electrons These two electron carriers donate electrons to the electron transport chain, which powers to the electron transport chain, which powers ATP synthesis via oxidative phosphorylationATP synthesis via oxidative phosphorylation

The Pathway of Electron The Pathway of Electron TransportTransport

The electron transport chain is in the cristae The electron transport chain is in the cristae of the mitochondrionof the mitochondrionThe carriers alternate reduced and oxidized The carriers alternate reduced and oxidized states as they accept and donate electronsstates as they accept and donate electrons

Electrons lose energy as they go down the Electrons lose energy as they go down the chain and are finally passed to Ochain and are finally passed to O22, forming , forming waterwaterThe electron transport chain generates no The electron transport chain generates no ATPATP

LE 9-13LE 9-13

ATP ATP ATP

GlycolysisOxidative

phosphorylation:electron transportand chemiosmosis

Citricacidcycle

NADH

50

FADH2

40 FMN

Fe•S

I FAD

Fe•S II

IIIQ

Fe•S

Cyt b

30

20

Cyt c

Cyt c1

Cyt a

Cyt a3

IV

10

0

Multiproteincomplexes

Fre

e en

erg

y (G

) re

lati

ve t

o O

2 (k

cal/m

ol)

H2O

O22 H+ + 1/2

ChemiosmosisChemiosmosisElectron transfer in the electron transport Electron transfer in the electron transport chain causes proteins to pump Hchain causes proteins to pump H++ from the from the mitochondrial matrix to the intermembrane mitochondrial matrix to the intermembrane spacespace

HH++ then moves back across the membrane, then moves back across the membrane, passing through channels in ATP synthase passing through channels in ATP synthase

ATP synthase uses the exergonic flow of HATP synthase uses the exergonic flow of H++ to drive phosphorylation of ATPto drive phosphorylation of ATP

This is an example of chemiosmosis, the use This is an example of chemiosmosis, the use of energy in a Hof energy in a H++ gradient to drive cellular gradient to drive cellular workwork

LE 9-14LE 9-14

INTERMEMBRANE SPACE

H+ H+

H+H+

H+

H+

H+

H+

ATP

MITOCHONDRAL MATRIX

ADP+

Pi

A rotor within the membrane spins as shown when H+ flows past it down the H+ gradient.

A stator anchored in the membrane holds the knob stationary.

A rod (or “stalk”) extending into the knob also spins, activating catalytic sites in the knob.

Three catalytic sites in the stationary knob join inorganic phosphate to ADP to make ATP.

The energy stored in a HThe energy stored in a H++ gradient gradient across a membrane couples the redox across a membrane couples the redox reactions of the electron transport reactions of the electron transport chain to ATP synthesischain to ATP synthesis

The HThe H++ gradient is referred to as a gradient is referred to as a proton-motive force, emphasizing its proton-motive force, emphasizing its capacity to do workcapacity to do work

1 NADH = 3 ATP1 FADH2 = 2 ATP

10 NADH = 30 ATP2 FADH2 = 4 ATP

34 ATP

Aerobic: existing in the presence of oxygen

Anaerobic: existing in the absence of oxygen

FermentationFermentation

• Cellular respiration requires OCellular respiration requires O22 to produce to produce ATPATP

• Glycolysis can produce ATP with or without Glycolysis can produce ATP with or without OO22 (in aerobic or anaerobic conditions) (in aerobic or anaerobic conditions)

• In the absence of OIn the absence of O22, glycolysis couples with , glycolysis couples with fermentation to produce ATPfermentation to produce ATP

FermentationFermentation

Anaerobic catabolism of organic Anaerobic catabolism of organic nutrientsnutrients

After pyruvate is produced in After pyruvate is produced in glycolysis, it is reduced, and NAD+ is glycolysis, it is reduced, and NAD+ is regeneratedregenerated– Prevents cell from depleting the pool of Prevents cell from depleting the pool of

NAD+, needed in glycolysisNAD+, needed in glycolysis– No additional ATP is producedNo additional ATP is produced

1. Pyruvate loses CO2 and is converted to the acetylaldehyde (2C)

2. NADH is oxidized to NAD+ and acetylaldehyde is reduced to ethanol (EtOH)

•Many bacteria and yeast carry out alcohol fermentation under anaerobic conditions

Alcohol FermentationAlcohol Fermentation

Yeast during brewing process

http://www.langhambrewery.co.uk/content/fermentation-yeast.jpg

Actively fermenting beer. The yeast mass is converting the sugars to alcohol and carbon dioxide. www.berkshirebrewingcompany.com/.../page4.html

1. NADH is oxidized to NAD+ and pyruvate is reduced to lactate (lactic acid)

•Commercially important products: cheese & yogurt•Human muscle cells switch to lactic acid fermentation when O2 is scarce. Lactate accumulates, slowly carried to liver and converted back to pyruvate when O2 is available

Organisms Classified by Oxygen Organisms Classified by Oxygen RequirementsRequirements

Strict (obligate) aerobesStrict (obligate) aerobes—require O—require O22 for growth and metabolismfor growth and metabolism

Strict (obligate) anaerobesStrict (obligate) anaerobes—only —only grow in the absence of Ogrow in the absence of O22 (O (O22 is is toxic)toxic)

Facultative anaerobesFacultative anaerobes—capable of —capable of growing in either aerobic or growing in either aerobic or anaerobic conditionsanaerobic conditions

Versatility of CatabolismVersatility of CatabolismStarchStarchglucose in glucose in digestive tractdigestive tractLiver converts Liver converts glycogenglycogenglucoseglucoseExcess Excess amino amino acidsacidspyruvate, acetyl pyruvate, acetyl CoA, and CoA, and αα--ketoglutarateketoglutarateFatsFatsglycerol + fatty glycerol + fatty acidsacidsGlycerolGlycerolglyceraldehydglyceraldehyde phosphatee phosphateFatty acidsFatty acidsacetyl CoA acetyl CoA (beta oxidation)(beta oxidation)

BiosynthesisBiosynthesis

Some organic molecules of food Some organic molecules of food provide carbon skeletons or raw provide carbon skeletons or raw materials for making new materials for making new macromoleculesmacromoleculesSome organic molecules from Some organic molecules from digestion used directly in anabolic digestion used directly in anabolic pathwayspathwaysSome precursors come from Some precursors come from glycolysis and Krebs Cycleglycolysis and Krebs CycleAnabolic pathways require ATP Anabolic pathways require ATP produced from catabolic pathwaysproduced from catabolic pathways

Feedback Mechanism Feedback Mechanism of Controlof Control

Ratio of ATP:ADP and Ratio of ATP:ADP and AMP reflects energy AMP reflects energy status and status and phosphofructokinasephosphofructokinase is sensitive to changes is sensitive to changes in the ratioin the ratio

Citrate and ATP = Citrate and ATP = allosteric inhibitorsallosteric inhibitors

ADP and AMP = ADP and AMP = allosteric activatorsallosteric activators

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Cellular Respiration: Harvesting Chemical Energy