PowerLecture:PowerLecture:Chapter 8Chapter 8
How Cells Release Stored EnergyHow Cells Release Stored Energy
More than 100 mitochondrial disorders are knownMore than 100 mitochondrial disorders are known
Friedreich’s ataxiaFriedreich’s ataxia, caused by a mutant gene, results in , caused by a mutant gene, results in loss of cordination, weak muscles, and visual problemsloss of cordination, weak muscles, and visual problems
Animal, plants, fungus, and most protists depend on Animal, plants, fungus, and most protists depend on structurally sound mitochondriastructurally sound mitochondria
Defective mitochondria can result in life threatening Defective mitochondria can result in life threatening disordersdisorders
Impacts, Issues: Impacts, Issues: When When Mitochondria Spin Their WheelsMitochondria Spin Their Wheels
Fig. 8-1, p.122
When Mitochondria Spin Their WheelsWhen Mitochondria Spin Their Wheels
Descendents of African honeybees that Descendents of African honeybees that
were imported to Brazil in the 1950swere imported to Brazil in the 1950s
More aggressive, wider-ranging than other More aggressive, wider-ranging than other
honeybeeshoneybees
Africanized bee’s muscle cells have large Africanized bee’s muscle cells have large
mitochondriamitochondria
““Killer” BeesKiller” Bees
Photosynthesizers get energy from the Photosynthesizers get energy from the sunsun
Animals get energy second- or third-hand Animals get energy second- or third-hand from plants or other organismsfrom plants or other organisms
Regardless, the energy is converted to the Regardless, the energy is converted to the chemical bond energy of ATPchemical bond energy of ATP
ATP Is Universal ATP Is Universal Energy SourceEnergy Source
Making ATPMaking ATP
Plants make ATP during photosynthesisPlants make ATP during photosynthesis
Cells of all organisms make ATP by Cells of all organisms make ATP by
breaking down carbohydrates, fats, and breaking down carbohydrates, fats, and
proteinprotein
Main Types of Main Types of Energy-Releasing Pathways Energy-Releasing Pathways
Aerobic pathwaysAerobic pathways
Evolved laterEvolved later Require oxygenRequire oxygen Start with glycolysis Start with glycolysis
in cytoplasmin cytoplasm Completed in Completed in
mitochondriamitochondria
Anaerobic pathwaysAnaerobic pathways
Evolved firstEvolved first Don’t require oxygenDon’t require oxygen Start with glycolysis in Start with glycolysis in
cytoplasmcytoplasm Completed in Completed in
cytoplasmcytoplasm
start (glycolysis) in cytoplasm
completed in mitochondrion
start (glycolysis) in cytoplasm
completed in cytoplasm
Aerobic Respiration
Anaerobic Energy-Releasing Pathways
Fig. 8-2, p.124
Main Types of Main Types of Energy-Releasing Pathways Energy-Releasing Pathways
Summary Equation for Aerobic Summary Equation for Aerobic RespirationRespiration
CC66HH12120066 + 6O + 6O22 6CO6CO22 + 6H + 6H2200
glucose oxygen glucose oxygen carbon water carbon water
dioxidedioxide
Overview of Aerobic Overview of Aerobic RespirationRespiration
CYTOPLASM
Glycolysis
Electron Transfer
Phosphorylation
KrebsCycle ATP
ATP
2 CO2
4 CO2
2
32
water
2 NADH
8 NADH
2 FADH2
2 NADH 2 pyruvate
e- + H+
e- + oxygen
(2 ATP net)
glucose
Typical Energy Yield: 36 ATP
e-
e- + H+
e- + H+
ATP
H+
e- + H+
ATP2 4
Fig. 8-3, p. 135
The Role of CoenzymesThe Role of Coenzymes
NADNAD++ and FAD accept electrons and and FAD accept electrons and
hydrogen hydrogen
Become NADH and FADHBecome NADH and FADH22
Deliver electrons and hydrogen to the Deliver electrons and hydrogen to the
electron transfer chain electron transfer chain
A simple sugarA simple sugar
(C(C66HH1212OO66))
Atoms held Atoms held together by together by covalent bondscovalent bonds
Glucose Glucose
In-text figurePage 126
Glycolysis Occurs Glycolysis Occurs in Two Stages in Two Stages
Energy-requiring stepsEnergy-requiring steps
ATP energy activates glucose and its six-carbon ATP energy activates glucose and its six-carbon
derivativesderivatives
Energy-releasing stepsEnergy-releasing steps
The products of the first part are split into three-The products of the first part are split into three-
carbon pyruvate moleculescarbon pyruvate molecules
ATP and NADH formATP and NADH form
GLUCOSE
glucose
GYCOLYSIS
pyruvate
to second stage of aerobicrespiration or to a differentenergy-releasing pathway
Fig. 8-4a, p.126
GlycolysisGlycolysis
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
Fig. 8-4b, p.127
GlycolysisGlycolysis
ATPADP
ENERGY-RELEASING STEPSOF GLYCOLYSIS
NAD+
P
PGAL
1,3–bisphosphoglycerate
substrate-levelphsphorylation
Pi
1,3–bisphosphoglycerate
ATP
NADHNADH
P
PGALNAD+
Pi
P PP P
3–phosphoglycerate 3–phosphoglycerate
P P
2 ATP invested
ADP
Fig. 8-4c, p.127
GlycolysisGlycolysis
2 ATP produced
ATPADP
P
substrate-levelphsphorylation
2–phosphoglycerate
ATP
P
pyruvate pyruvate
ADP
P P
2–phosphoglycerate
H2O H2O
PEP PEP
Fig. 8-4d, p.127
GlycolysisGlycolysis
Glycolysis: Net Energy Yield Glycolysis: Net Energy Yield
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
Second Stage Reactions Second Stage Reactions
Preparatory reactionsPreparatory reactionsPyruvate is oxidized into two-carbon acetyl Pyruvate is oxidized into two-carbon acetyl
units and carbon dioxideunits and carbon dioxideNADNAD++ is reduced is reduced
Krebs cycleKrebs cycleThe acetyl units are oxidized to carbon The acetyl units are oxidized to carbon
dioxidedioxideNADNAD++ and FAD are reducedand FAD are reduced
innermitochondrial
membrane
outermitochondrial
membrane
innercompartment
outercompartment
Fig. 8-6a, p.128
Second Stage Reactions Second Stage Reactions
Preparatory ReactionsPreparatory Reactions
pyruvate
NAD+
NADH
coenzyme A (CoA)
O O carbon dioxide
CoAacetyl-CoA
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
Acetyl-CoAFormation
acetyl-CoA
(CO2)
pyruvate
coenzyme A NAD+
NADH
CoA
Krebs CycleCoA
NADH
FADH2
NADH
NADH
ATP ADP + phosphategroup
NAD+
NAD+
NAD+
FAD
oxaloacetate citrate
Fig. 8-7a, p.129
Preparatory Preparatory ReactionsReactions
Results of the Second StageResults of the Second Stage
All of the carbon molecules in pyruvate All of the carbon molecules in pyruvate end up in carbon dioxideend up in carbon dioxide
Coenzymes are reduced (they pick up Coenzymes are reduced (they pick up electrons and hydrogen)electrons and hydrogen)
One molecule of ATP forms One molecule of ATP forms Four-carbon oxaloacetate regeneratesFour-carbon oxaloacetate regenerates
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. 8-6b, p.128
Coenzyme Reductions during Coenzyme Reductions during First Two StagesFirst Two Stages
GlycolysisGlycolysis 2 NADH2 NADHPreparatoryPreparatory
reactionsreactions 2 NADH2 NADHKrebs cycleKrebs cycle 2 FADH 2 FADH22 + 6 NADH + 6 NADH
TotalTotal 2 FADH 2 FADH22 + 10 NADH + 10 NADH
glucose
glycolysis
e–
KREBSCYCLE
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+
Fig. 8-9, p.131
PhosphorylationPhosphorylation
Occurs in the mitochondriaOccurs in the mitochondriaCoenzymes deliver electrons to electron Coenzymes deliver electrons to electron
transfer chainstransfer chains
Electron Transfer Electron Transfer Phosphorylation Phosphorylation
Creating an HCreating an H++ Gradient Gradient
NADH
OUTER COMPARTMENT
INNER COMPARTMENT
Electron transfer sets up HElectron transfer sets up H++ ion gradients ion gradients
Making ATP: Making ATP: Chemiosmotic ModelChemiosmotic Model
ATP
ADP+Pi
INNER COMPARTMENT
Flow of HFlow of H++ down gradients powers ATP formation down gradients powers ATP formation
Importance of OxygenImportance of Oxygen
Electron transport phosphorylation Electron transport phosphorylation requires the presence of oxygenrequires the presence of oxygen
Oxygen withdraws spent electrons from Oxygen withdraws spent electrons from the electron transfer chain, then combines the electron transfer chain, then combines with Hwith H++ to form water to form water
Do not use oxygenDo not use oxygen
Produce less ATP than aerobic pathwaysProduce less ATP than aerobic pathways
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 carbon Do not break glucose down completely to carbon
dioxide and waterdioxide 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++
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
Fig. 8-10d, p.132
Alcoholic Alcoholic FermentationFermentation
C6H12O6
ATP
ATPNADH
2 lactate
electrons, hydrogen from NADH
2 NAD+
2
2 ADP
2 pyruvate
2
4
energy output
energy input
glycolysis
lactate fermentation
2 ATP net
Fig. 8-11, p.133
Lactate Lactate FermentationFermentation
Anaerobic Electron TransportAnaerobic Electron Transport
Carried out by certain bacteriaCarried out by certain bacteria
Electron transfer chain is in bacterial Electron transfer chain is in bacterial plasma membrane plasma membrane
Final electron acceptor is compound from Final electron acceptor is compound from environment (such as nitrate), not oxygenenvironment (such as nitrate), not oxygen
ATP yield is lowATP yield is low
Summary of Energy HarvestSummary of Energy Harvest(per molecule of glucose)(per molecule of glucose)
GlycolysisGlycolysis2 ATP formed by substrate-level phosphorylation2 ATP formed by substrate-level phosphorylation
Krebs cycle and preparatory reactionsKrebs cycle and preparatory reactions2 ATP formed by substrate-level phosphorylation2 ATP formed by substrate-level phosphorylation
Electron transport phosphorylationElectron transport phosphorylation32 ATP formed32 ATP formed
Energy Harvest VariesEnergy Harvest Varies
NADH formed in cytoplasm cannot enter NADH formed in cytoplasm cannot enter mitochondrionmitochondrion
It delivers electrons to mitochondrial It delivers electrons to mitochondrial membranemembrane
Membrane proteins shuttle electrons to Membrane proteins shuttle electrons to NADNAD++ 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
FOOD
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
waterH+
e– + oxygen
e–
4
ATP2
Fig. 8-13b, p.135
electron transfer phosphorylation
Alternative Alternative Energy Energy
SourcesSources
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 acceptor in Cells arose that used oxygen as final acceptor in
electron transportelectron transport
Evolution of Metabolic Evolution of Metabolic Pathways Pathways
p.136b
Processes Are Linked Processes Are Linked
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