Cell Respiration APBio

Chapter 8

Harvesting Harvesting EnergyEnergy

Chapter 8 2 Overview of Glucose BreakdownOverview of Glucose Breakdown

The overall equation for the complete The overall equation for the complete breakdown of glucose is:breakdown of glucose is:

CC66HH1212OO66 + 6O + 6O22 6CO 6CO22 + 6H + 6H22O + ATPO + ATP

The main stages of glucose metabolism The main stages of glucose metabolism are:are:• GlycolysisGlycolysis• Cellular respirationCellular respiration

Chapter 8 3


GlycolysisGlycolysis• Occurs in the cytosol Occurs in the cytosol • Does not require oxygenDoes not require oxygen• Breaks glucose into pyruvateBreaks glucose into pyruvate• Yields two molecules of ATP per molecule Yields two molecules of ATP per molecule

of glucose of glucose


If oxygen is absent fermentation occursIf oxygen is absent fermentation occurs• pyruvate is converted into either lactate, or pyruvate is converted into either lactate, or

into ethanol and COinto ethanol and CO22

If oxygen is present cellular respiration If oxygen is present cellular respiration occurs…occurs…


Cellular respiration Cellular respiration • Occurs in Occurs in mitochondriamitochondria (in eukaryotes) (in eukaryotes)• Requires oxygenRequires oxygen• Breaks down pyruvate into carbon dioxide Breaks down pyruvate into carbon dioxide

and waterand water• Produces an additional 32 or 34 ATP Produces an additional 32 or 34 ATP

molecules, depending on the cell type molecules, depending on the cell type

Chapter 8 7 GlycolysisGlycolysis

Overview of the two major phases of Overview of the two major phases of glycolysis glycolysis

• Glucose activation phaseGlucose activation phase• Energy harvesting phaseEnergy harvesting phase


Glucose activation phaseGlucose activation phase• Glucose molecule converted to highly Glucose molecule converted to highly

reactive fructose bisphosphate by two reactive fructose bisphosphate by two enzyme-catalyzed reactions, using 2 enzyme-catalyzed reactions, using 2 ATPsATPs

Chapter 8 9

Essentials of Glycolysis (a)Essentials of Glycolysis (a)

CC CC CC CC CC CCGlucoseGlucose PP

PP

ATPATP ADPADP

CC CC CC CC CC CC

Glucose-6-Glucose-6-PhosphatePhosphate

PP

CC CC CC CC CC CC

Glucose-6-Glucose-6-PhosphatePhosphate

ATPATP ADPADP

PP

CC CC CC CC CC CC

Fructose-1,6-Fructose-1,6-BisphosphateBisphosphate


Energy harvesting phaseEnergy harvesting phase• Fructose bisphosphate is split into two Fructose bisphosphate is split into two

three-carbon molecules of glyceraldehyde 3-three-carbon molecules of glyceraldehyde 3-phosphate (G3P)phosphate (G3P)

• In a series of reactions, each G3P molecule In a series of reactions, each G3P molecule is converted into a pyruvate, generating two is converted into a pyruvate, generating two ATPs per conversion, for a total of four ATPsATPs per conversion, for a total of four ATPs

• Because two ATPs were used to activate the Because two ATPs were used to activate the glucose molecule there is a net gain of two glucose molecule there is a net gain of two ATPs per glucose moleculeATPs per glucose molecule

Chapter 8 11

Essentials of Glycolysis (Essentials of Glycolysis (bb))

PP

PP

CC CC CC CC CC CC

Fructose-1,6-Fructose-1,6-BisphosphateBisphosphate

PP

CC CC CC

PP

CC CC CC

PP

CC CC CC

PP

CC CC CCG3PG3P


Energy harvesting phase (continued)Energy harvesting phase (continued)• As each G3P is converted to pyruvate, As each G3P is converted to pyruvate,

two high-energy electrons and a two high-energy electrons and a hydrogen ion are added to an “empty” hydrogen ion are added to an “empty” electron-carrier NAD+ to make the high-electron-carrier NAD+ to make the high-energy electron-carrier molecule NADHenergy electron-carrier molecule NADH

• Because two G3P molecules are Because two G3P molecules are produced per glucose molecule, two produced per glucose molecule, two NADH carrier molecules are formedNADH carrier molecules are formed

Chapter 8 13

Essentials of Glycolysis (c)Essentials of Glycolysis (c)

PPPP

PP

CC CC CC

PP

CC CC CC

PP

CC CC CC

PP

CC CC CC

CC CC CC CC CC CC

PPiiPPii

NADNAD++NADNAD++

NADHNADHNADHNADH

ATPATPATPATP

ATPATPATPATP

ADPADPADPADP

ADPADPADPADP

PyruvatesPyruvates

G3PG3P


Summary of glycolysis:Summary of glycolysis:• Each molecule of glucose is broken Each molecule of glucose is broken

down to two molecules of pyruvatedown to two molecules of pyruvate• A net of two ATP molecules and two A net of two ATP molecules and two

NADH (high-energy electron carriers) are NADH (high-energy electron carriers) are formedformed

Chapter 8 15

Fermentation of DoughFermentation of Dough

Chapter 8 16 FermentationFermentation

Pyruvate is processed differently under Pyruvate is processed differently under aerobic and anaerobic conditionsaerobic and anaerobic conditions

Under aerobic conditions, the high Under aerobic conditions, the high energy electrons in NADH produced in energy electrons in NADH produced in glycolysis are ferried to ATP-glycolysis are ferried to ATP-generating reactions in the generating reactions in the mitochondria, making NAD+ available mitochondria, making NAD+ available to recycle in glycolysisto recycle in glycolysis


Under anaerobic conditions, pyruvate is Under anaerobic conditions, pyruvate is converted into lactate or ethanol, a converted into lactate or ethanol, a process called fermentationprocess called fermentation

Fermentation does not produce more Fermentation does not produce more ATP, but is necessary to regenerate ATP, but is necessary to regenerate the high-energy electron carrier the high-energy electron carrier molecule NAD+, which must be molecule NAD+, which must be available for glycolysis to continue available for glycolysis to continue


Some microbes ferment pyruvate to other Some microbes ferment pyruvate to other acids (as seen in making of cheese, acids (as seen in making of cheese, yogurt, sour cream)yogurt, sour cream)

Some microbes perform fermentation Some microbes perform fermentation exclusively (instead of aerobic exclusively (instead of aerobic respiration)respiration)

Yeast cells perform Yeast cells perform alcoholic fermentationalcoholic fermentation

Chapter 8 19

Alcoholic FermentationAlcoholic Fermentation

NADNAD++

CC CC CC CC CC CC

GlucosesGlucoses

CC CC CC

GlycolysisGlycolysis AlcoholicAlcoholicFermentationFermentation

NADNAD++ NADHNADH

ADPADP ATPATP

ADPADP ATPATP

PyruvatesPyruvates EthanolsEthanolsCC CC CC CC CC

CC CC

NADNAD++NADNAD++ NADHNADH

CCO

O CCO

O

NADHNADHNADHNADH


Some cells ferment pyruvate to form Some cells ferment pyruvate to form acidsacids

Human muscle cells can perform Human muscle cells can perform fermentationfermentation

• Anaerobic conditions produced when Anaerobic conditions produced when muscles use up Omuscles use up O22 faster than it can be faster than it can be delivered (e.g. while sprinting)delivered (e.g. while sprinting)

• Lactate (lactic acid) produced from Lactate (lactic acid) produced from pyruvatepyruvate

Chapter 8 21

Lactate FermentationLactate Fermentation

NADNAD++

CC CC CC CC CC CC

GlucosesGlucoses

CC CC CC

CC CC CCGlycolysisGlycolysis LactateLactate

FermentationFermentation

NADNAD++ NADHNADH

ADPADP ATPATP

ADPADP ATPATP

PyruvatesPyruvates LactatesLactatesCC CC CC

CC CC CC

NADNAD++NADNAD++ NADHNADH

NADHNADHNADHNADH

Chapter 8 22 Cellular RespirationCellular Respiration

In eukaryotic cells, cellular respiration In eukaryotic cells, cellular respiration occurs within occurs within mitochondriamitochondria, organelles , organelles with two membranes that produce two with two membranes that produce two compartmentscompartments

• The inner membrane encloses a central The inner membrane encloses a central compartment containing the fluid compartment containing the fluid matrixmatrix

• The outer membrane surrounds the The outer membrane surrounds the organelle, producing an organelle, producing an intermembrane intermembrane spacespace

Chapter 8 23

A MitochondrionA Mitochondrion

MatrixMatrix

A CellA Cell

One of ItsOne of ItsMitochondriaMitochondria

A CristaA Crista

OuterOuter& Inner& Inner

MembranesMembranes

IntermembraneIntermembraneCompartmentCompartment

aabb

cc


Overview of Aerobic Cellular Overview of Aerobic Cellular Respiration:Respiration:

Glucose is first broken down into Glucose is first broken down into pyruvate, through pyruvate, through glycolysisglycolysis, in the , in the cell cytoplasmcell cytoplasm

Pyruvate is transported into the Pyruvate is transported into the mitochondrion (eukaryotes) and split mitochondrion (eukaryotes) and split into COinto CO22 and a 2 carbon acetyl group and a 2 carbon acetyl group


The acetyl group is further broken down The acetyl group is further broken down into COinto CO22 in the in the Krebs CycleKrebs Cycle (matrix (matrix space) as electron carriers are loadedspace) as electron carriers are loaded

Electron carriers loaded up in glycolysis Electron carriers loaded up in glycolysis and the Krebs Cycle give up and the Krebs Cycle give up electrons to the electrons to the electron transport electron transport chainchain (ETC) along the inner (ETC) along the inner mitochondrial membranemitochondrial membrane


A hydrogen ion gradient produced by the A hydrogen ion gradient produced by the ETC is used to make ATP ETC is used to make ATP ((chemiosmosischemiosmosis))

ATP is transported out of the ATP is transported out of the mitochondrion to provide energy for mitochondrion to provide energy for cellular activitiescellular activities

Chapter 8 27

Cellular Cellular RespirationRespiration

Chapter 8 28 Pyruvate Breakdown in MitochondriaPyruvate Breakdown in Mitochondria

After glycolysis, pyruvate diffuses into After glycolysis, pyruvate diffuses into the mitochondrion into the matrix the mitochondrion into the matrix spacespace

Pyruvate is split into COPyruvate is split into CO22 and a 2-carbon and a 2-carbon acetyl group, generating 1 NADH per acetyl group, generating 1 NADH per pyruvatepyruvate


Acetyl group is carried by a helper Acetyl group is carried by a helper molecule called Coenzyme A, now molecule called Coenzyme A, now called Acetyl CoAcalled Acetyl CoA

Acetyl CoA enters the Krebs Cycle and is Acetyl CoA enters the Krebs Cycle and is broken down into CObroken down into CO22


Electron carriers NADElectron carriers NAD++ and FAD are and FAD are loaded with electrons to produce 3 loaded with electrons to produce 3 NADH & 1 FADHNADH & 1 FADH22 per Acetyl CoA per Acetyl CoA

6. One ATP also made per Acetyl CoA 6. One ATP also made per Acetyl CoA in the Krebs Cyclein the Krebs Cycle

Chapter 8 31

Formation of Acetyl CoAFormation of Acetyl CoA

CC CC CC CC CC CC

CoACoACoACoA

CC CC CC CC CC CCPyruvatesPyruvates

CoACoACoACoA

CC CC CC CC

NADNAD++NADNAD++

NADHNADHNADHNADH

CCOO

OOCC

OO

OO

Acetyl CoAAcetyl CoA

CC CC CC CC

Chapter 8 32

Krebs Cycle: SummaryKrebs Cycle: Summary

CC CC CC CCCC

NADHNADH

CC CC CC CC

CoACoA

CCCC CC CC CCCC

CCO

O

CCO

O

NADNAD++

NADHNADH

NADNAD++

NADHNADH

ADPADP

ATPATP

HH22OO

NADNAD++

FADHFADH22

FADFAD

HH22OO

CC CC CC CC

CCCC CC CC CCCC

CoACoA

NADNAD++

NADHNADH

CCO

O

CC CC CC CCCC

HH22OO

NADNAD++

NADHNADH

ADPADP

ATPATP

CCO

O

CC CC CCCC

NADHNADH

NADNAD++

FADHFADH22

FADFAD

HH22OO

1

2 3

4

5 6 7

CCCC CC CC CCCCCC CC CC CCCC

CC CC CCCC

CoACoACoACoA CC CC CC CCAcetyl CoAAcetyl CoA

Chapter 8 33 Electron Transport ChainElectron Transport Chain

Most of the energy in glucose is stored Most of the energy in glucose is stored in electron carriers NADH and FADHin electron carriers NADH and FADH22

• Only 4 total ATP produced per glucose Only 4 total ATP produced per glucose after complete breakdown in the Krebs after complete breakdown in the Krebs CycleCycle

Chapter 8 34 Electron Transport ChainElectron Transport Chain

NADH and FADHNADH and FADH22 deposit electrons into deposit electrons into electron transport chainselectron transport chains in the inner in the inner mitochondrial membranemitochondrial membrane

Electrons join with oxygen gas and Electrons join with oxygen gas and hydrogen ions to made Hhydrogen ions to made H22O at the end O at the end of the ETCsof the ETCs

Chapter 8 35

MitochondrialMitochondrialElectron Transport SystemElectron Transport System

Chapter 8 36 ChemiosmosisChemiosmosis

Energy is released from electrons as they Energy is released from electrons as they are passed down the electron are passed down the electron transport chaintransport chain

Released energy used to pump hydrogen Released energy used to pump hydrogen ions across the inner membrane ions across the inner membrane

• Hydrogen ions accumulate in Hydrogen ions accumulate in intermembrane spaceintermembrane space


Hydrogen ions form a concentration Hydrogen ions form a concentration gradient across the membrane, a form gradient across the membrane, a form of stored energyof stored energy

Hydrogen ions flow back into the matrix Hydrogen ions flow back into the matrix through an ATP synthesizing enzymethrough an ATP synthesizing enzyme

• Process is called Process is called chemiosmosischemiosmosis


Flow of hydrogen ions provides energy Flow of hydrogen ions provides energy to link 32-34 molecules of ADP with to link 32-34 molecules of ADP with phosphate, forming 32-34 ATPphosphate, forming 32-34 ATP

ATP then diffuses out of mitochondrion ATP then diffuses out of mitochondrion and used for energy-requiring and used for energy-requiring activities in the cellactivities in the cell

Chapter 8 39

MitochondrialMitochondrialChemiosmosis (1)Chemiosmosis (1)

Chapter 8 40


Chapter 8 41


Chapter 8 42

Influence on How Organisms FunctionInfluence on How Organisms Function

Metabolic processes in cells are heavily Metabolic processes in cells are heavily dependent on ATP generation (cyanide dependent on ATP generation (cyanide kills by preventing this)kills by preventing this)

Muscle cells switch between fermentation Muscle cells switch between fermentation and aerobic cell respiration depending and aerobic cell respiration depending on Oon O22 availability availability

Chapter 8 43

Energy Harvested Energy Harvested from Glucosefrom Glucose

Chapter 8 44

Energy Harvested from GlucoseEnergy Harvested from Glucose

(Cytoplasm)(Cytoplasm) GlucoseGlucose

2 NADH2 NADH2 NADH2 NADH6 NADH6 NADH2 FADH2 FADH22

2 Pyruvates2 Pyruvates

2 CO2 CO22

4 CO4 CO22

2 ATP2 ATP 4 ATP4 ATP

(Mitochondrial(MitochondrialMatrix)Matrix)

(Inner(InnerMembrane)Membrane)

2 ATP2 ATP

32 ATP32 ATPElectron TransportElectron Transport

SystemSystem

GlycolysisGlycolysis

KrebsKrebsCycleCycle

WaterWater

OxygenOxygen

Chapter 8

The endThe end

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Cell Respiration APBio