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8/9/2019 Plant Cellular Respiration
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PLANT CELLULAR RESPIRATION:
How Plants Harvest Chemical Energyto Generate ATP
Plants obtain ATP and other energy carriers by respiration,
just as animals (including man) do.
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Fig. 9-2
Lightenergy
ECOSYSTEM
Photosynthesisin chloroplasts
CO2 + H2O
Cellular respirationin mitochondria
Organicmolecules
+ O2
ATP powers most cellular work
Heatenergy
ATP
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A Review
Photosynthesis
- process of incorporating energy from light into energy-rich moleculeslike glucose.
6 CO2 + 6 H2O + light C6H12O6 + 6O2
Respiration
- opposite process
- extraction of the stored energy from glucose to form ATP
(from ADP and Pi).
C6H12O6 + 6O2 6 CO2 + 6 H2O + energy
- generally considered to begin with glucose.
- a complicated process, basically the oxidation of glucose.
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Respiration: The Oxidation of Glucose
Oxidation of glucose basically involves:
• splitting apart of the glucose molecule
• removal of hydrogen atoms (i.e., electrons and protons)from carbon atoms, and
• combining of H+ with oxygen, which is thereby reduced.
• As the glucose molecule is oxidized, some of its energyis extracted in a series of small, discrete steps and isstored in the phosphoanhydride bonds of ATP.
• However, most of its energy is dissipated as heatenergy.
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A General Overview of Respiration
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Fig. 9-6-1
Substrate-levelphosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electrons
carriedvia NADH
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Fig. 9-6-2
Mitochondrion
Substrate-levelphosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electrons
carriedvia NADH
Substrate-levelphosphorylation
ATP
Electrons carried
via NADH andFADH2
Citricacid
cycle
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Fig. 9-6-3
Mitochondrion
Substrate-levelphosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electrons
carriedvia NADH
Substrate-levelphosphorylation
ATP
Electrons carried
via NADH andFADH2
Oxidativephosphorylation
ATP
Citricacid
cycle
Oxidativephosphorylation:electron transport
andchemiosmosis
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Types of Respiration• Aerobic respiration
- requires O2 as the terminal e- acceptor.
- oxygen as the ultimate e- acceptor:- the reaction is highly exergonic (energy-yielding); -686 kcal/mole.
• Anaerobic respiration
- respiration w/out O2; often called fermentation.
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obligate (strict) aerobes – animals and plants
obligate (strict) anaerobes – certain bacteria
facultatively aerobes or facultatively anaerobes
– many fungi; some plants; certain types of animal tissues.
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Stages of Aerobic Respiration
Stage 1: Glycolysisbreakdown of the 6-C glucose molecule to two
3-C molecules of pyruvic acid or pyruvate
Stage 2: Krebs Cycle or Citric Acid Cycle
further breakdown of the remnants of glucosemolecule to CO2 and H2O, resulting toelectrons.
Stage 3: Electron Transport System/Chain
passage of resulting electrons from Stage 2.Stage 4: Oxidative Phosphorylation
The energy that is released as electrons movethrough the ETS and is used to form ATP fromADP and phosphate.
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Pathways of of Anaerobic Respiration
• Ethanol Fermentation
- conversion of pyruvate to ethanol
- occurs in most plants, fungi (such as yeasts),
bacteria
• Lactate Fermentation
- conversion of pyruvate to lactate
- occurs in animals, many bacteria, fungi,protists
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h
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Glycolysis
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Glycolysis
• from glyco , meaning “sugar”; and lysis , meaning
“splitting”.• Embden-Meyerhoff pathway.
• splitting of the six-carbon glucose into twomolecules of pyruvate, in a series of steps, eachcatalyzed by a specific enzyme.
• The reactions serve as the initial, identical stepsof both aerobic and anaerobic respiration.
• occurs in the cytosol.
• carried out by virtually all living cells
(from bacteria to the eukaryotic plant and animalcells).
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Glycolysis
• considered as a primitive pathway:- probably arose before the appearance ofatmospheric O2 and before the origin of cellularorganelles.
- reactions 4 to 7 also occur in the Calvin cycle,illustrating the principle of biochemical evolution:pathways do not arise entirely anew; rather, a few new reactions are added to an existing set to make a “new” pathway.
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Resemblance between the Glycolytic Pathway & Calvin Cycle
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GLYCOLYSIS
Phase 1: Preparatory Phase
Energy Investment (2 ATP)
Step 1: preparatory phosphorylation- transfer of a phosphate group to
glucose from an ATP molecule
-> energizing glucose (phosphate bond).
Step 2: rearrangement of G6-phosphate toF6-phosphate.
Step 3: 2nd preparatory reaction- F6-phosphate gains a second
phosphate by investment of anotherATP, producing F1,6-bisphosphate.
Step 4: cleavage step from whichglycolysis derives its name.
- 6-C sugar molecule is split in half,producing two 3-C molecules,
glyceraldehyde 3-phosphate(PGAL)and dihydroxyacetone phosphate(DHAP).
Step 5: interconversion of PGAL, buteventually leading to the conversion to
PGAL.
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GLYCOLYSIS
Phase 2: Payoff Phase
Energy Yield (4 ATP & 2 NADH per glucose)
Step 6: - oxidation of glyceraldehyde 3-phosphate
(PGAL) to 1,3-bisPGA ;-reduction of NAD+ to NADH and H+.
-2 NADH and 2 H + per glucose
-attachment of phosphate grp to C-1 of 1,3-bisphosphoglycerate-> energizing the molecule.
Step 7: substrate-level phosphorylation, involving
the enzymatic transfer of phosphate grp fromthe 1,3-bisphosphate to ADP, forming ATP.
(1st ATP-forming rxn)
Step 8: - transfer of the remaining phosphate grpfrom C-3 to C-2 of glycerate (PGA).
Step 9: - removal of H2O from the 3-C cpd.,
2-phosphoglycerate, resulting to the formationof phosphoenolpyruvate (PEP).
(high-energy, phosphorylated cpd )
Step 10 : substrate-level phosphorylation,transfer of phosphate grp of PEP to ADP,
forming another ATP.(2 nd ATP-forming rxn)
Fig. 9-8
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Fig. 9 8
Energy investment phase
Glucose
2 ADP + 2 P 2 ATP used
formed4 ATP
Energy payoff phase
4 ADP + 4 P
2 NAD+ + 4 e – + 4 H+ 2 NADH + 2 H+
2 Pyruvate + 2 H2
O
2 Pyruvate + 2 H2OGlucoseNet
4 ATP formed – 2 ATP used 2 ATP
2 NAD+ + 4 e – + 4 H+ 2 NADH + 2 H+
Fig. 9-9-1
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Fig. 9 9 1
ATP
ADP
Hexokinase
1
ATP
ADP
Hexokinase
1
Glucose
Glucose-6-phosphate
Glucose
Glucose-6-phosphate
Fig. 9-9-2
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g 9 9
Hexokinase
ATP
ADP
1
Phosphoglucoisomerase
2
Phosphogluco-isomerase
2
Glucose
Glucose-6-phosphate
Fructose-6-phosphate
Glucose-6-phosphate
Fructose-6-phosphate
Fig. 9-9-3
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1
g
Hexokinase
ATP
ADP
Phosphoglucoisomerase
Phosphofructokinase
ATP
ADP
2
3
ATP
ADP
Phosphofructo-kinase
Fructose-1, 6-bisphosphate
Glucose
Glucose-6-phosphate
Fructose-6-phosphate
Fructose-1, 6-bisphosphate
1
2
3
Fructose-6-phosphate
3
Fig. 9-9-4
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g
Glucose
ATP
ADP
Hexokinase
Glucose-6-phosphate
Phosphoglucoisomerase
Fructose-6-phosphate
ATP
ADP
Phosphofructokinase
Fructose-1, 6-bisphosphate
Aldolase
Isomerase
Dihydroxyacetonephosphate
Glyceraldehyde-3-phosphate
1
2
3
4
5
Aldolase
Isomerase
Fructose-1, 6-bisphosphate
Dihydroxyacetonephosphate
Glyceraldehyde-3-phosphate
4
5
Fig. 9-9-5
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g
2 NAD+
NADH2
+ 2 H+
2
2 P i
Triose phosphatedehydrogenase
1, 3-Bisphosphoglycerate
6
2 NAD+
Glyceraldehyde-3-phosphate
Triose phosphate
dehydrogenaseNADH2
+ 2 H+
2 P i
1, 3-Bisphosphoglycerate
6
2
2
Fig. 9-9-6
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2 NAD+
NADH2
Triose phosphatedehydrogenase
+ 2 H+
2 Pi
2
2 ADP
1, 3-Bisphosphoglycerate
Phosphoglycerokinase
2 ATP
2 3-Phosphoglycerate
6
7
2
2 ADP
2 ATP
1, 3-Bisphosphoglycerate
3-Phosphoglycerate
Phosphoglycero-kinase
2
7
Fig. 9-9-7
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3-Phosphoglycerate
Triose phosphatedehydrogenase
2 NAD+
2 NADH
+ 2 H+
2 P i
2
2 ADP
Phosphoglycerokinase
1, 3-Bisphosphoglycerate
2 ATP
3-Phosphoglycerate2
Phosphoglyceromutase
2-Phosphoglycerate2
2-Phosphoglycerate2
2
Phosphoglycero-mutase
6
7
8
8
Fig. 9-9-8
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2 NAD+
NADH2
2
2
2
2
+ 2 H+
Triose phosphatedehydrogenase
2 P i
1, 3-Bisphosphoglycerate
Phosphoglycerokinase
2 ADP
2 ATP
3-Phosphoglycerate
Phosphoglyceromutase
Enolase
2-Phosphoglycerate
2 H2O
Phosphoenolpyruvate
9
8
7
6
2 2-Phosphoglycerate
Enolase
2
2 H2O
Phosphoenolpyruvate
9
Fig. 9-9-9
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Triose phosphatedehydrogenase
2 NAD+
NADH2
2
2
2
2
2
2 ADP
2 ATP
Pyruvate
Pyruvate kinase
Phosphoenolpyruvate
Enolase2 H2O
2-Phosphoglycerate
Phosphoglyceromutase
3-Phosphoglycerate
Phosphoglycerokinase
2 ATP
2 ADP
1, 3-Bisphosphoglycerate
+ 2 H+
6
7
8
9
10
2
2 ADP
2 ATP
Phosphoenolpyruvate
Pyruvatekinase
2 Pyruvate
10
2 Pi
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GLYCOLYSIS: Summary• Glycolysis takes 1 glucose and turns it into 2 three-carbon molecules of
pyruvate; occurs in the cytosol.
• Steps:1) 2 ATP are added.
2) 2 NADH are produced.
3) 4 ATP are produced.
4) 2 pyruvate are formed.
How many ATP are formed ?
Net gain: 2 NADH and a net of 2 ATP (made 4 ATP, but used 2 ATP)
Overall Equation:
Glucose + 2 NAD+ + 2 ADP + 2 P
-----> 2 pyruvate + 2 NADH + 2 ATP + 2 H+ + 2 H2O
• 2 moles of pyruvate have 546 kilocalories, 80% of the energy stored in theoriginal glucose molecule (686 kilocalories).
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The Krebs Cycle
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The Structure of the Mitochondrion Provides the Key to Its Function
The mitochondrion resembles a self-contained chemical factory.
• outer membrane – permeable to most small molecules.
• intermembrane space – similar in composition to the cytosol.
• inner membrane (crista) – permits the passage only of certain
molecules, e.g., pyruvate, electron carriers, ADP, and ATP; it restrainsthe passage of other molecules and ions, including H+ ions (protons). critical to the ability of mitochondria to harness the power of respiration for ATP production.
• matrix – contains water, enzymes, coenzymes, phosphates, other
molecules involved in respiration.
K b C l
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Krebs Cycle- Postulated by Sir Hans Krebs in 1937.
- can also be called Citric Acid Cycle or Tricarboxylic Acid Cycle (TCA),because it begins with the formation of citric acid or citrate, and several of
the intermediates are tricarboxylic acids – each has 3 carboxyl groups.
Preliminary Step:
• Transport of pyruvate from the cytosol, across the mitochondrialmembranes into the mitochondrial matrix.
• Oxidation and Decarboxylation of Pyruvate to AcetylCoA.- electrons are removed
- 2 CO2 is split out of the molecule
- 2 NADH are formed.
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CYTOSOL MITOCHONDRION
NAD+ NADH + H+
2
1 3
Pyruvate
Transport protein
CO2Coenzyme A
Acetyl CoA
Steps in the Krebs Cycle:
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Steps in the Krebs Cycle:
• Acetyl group (2-C) is combined w/ a 4-C cpd.OAA to produce citrate (6-C).
• The coA is released to combine with a newacetyl grp when another molecule of
pyruvate is oxidized.• 7 intermediate products.
Decarboxylation rxns:
- isocitrate to alpha-ketoglutarate (3)
- ketoglutarate to succinylCoA (4)
Dehydrogenation (oxidation) rxns:
- isocitrate to alpha-ketoglutarate (3)
- ketoglutarate to succinylCoA (4)
-succinate to fumarate (6)
- malate to OAA (8)
• Substrate-level Phosphorylation : poweredby the energy released by breakdown of
succinylCoA to succinate & CoA (5).• 3 NADH, 1 FADH2, 1 ATP, 2 CO2 are
formed.
Two of the 6 C are removed and oxidized to CO2and OAA is regenerated. The cycle repeats.Each turn of the cycle uses up 1 acetyl grp
and regenerates 1 OAA molecule.
Fig. 9-12-1
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Acetyl CoA
Oxaloacetate
CoA—SH
1
Citrate
Citricacidcycle
Fig. 9-12-2
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Acetyl CoA
Oxaloacetate
Citrate
CoA—SH
Citricacidcycle
1
2
H2O
Isocitrate
Fig. 9-12-3
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Acetyl CoA
CoA—SH
Oxaloacetate
Citrate
H2O
Citricacidcycle
Isocitrate
1
2
3
NAD+
NADH
+ H+
-Keto-glutarate
CO2
Fig. 9-12-4
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Acetyl CoA
CoA—SH
Oxaloacetate
Citrate
H2O
IsocitrateNAD+
NADH
+ H+
Citricacidcycle
-Keto-glutarate
CoA—SH
1
2
3
4
NAD+
NADH
+ H+SuccinylCoA
CO2
CO2
Fig. 9-12-5
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Acetyl CoA
CoA—SH
Oxaloacetate
Citrate
H2O
IsocitrateNAD+
NADH
+ H+
CO2
Citricacidcycle
CoA—SH
-Keto-glutarate
CO2NAD+
NADH
+ H+SuccinylCoA
1
2
3
4
5
CoA—SH
GTP GDP
ADP
P iSuccinate
ATP
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Fig. 9-12-7
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Acetyl CoA
CoA—SH
Oxaloacetate
Citrate
H2O
IsocitrateNAD+
NADH
+ H+
CO2
-Keto-glutarate
CoA—SH
NAD+
NADH
SuccinylCoA
CoA—SH
PP
GDPGTP
ADP
ATP
Succinate
FADFADH2
Fumarate
CitricacidcycleH2O
Malate
1
2
5
6
7
i
CO2
+ H+
3
4
Fig. 9-12-8
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Acetyl CoA
CoA—SH
Citrate
H2O
IsocitrateNAD+
NADH
+ H+
CO2
-Keto-glutarate
CoA—SH
CO2NAD+
NADH
+ H+SuccinylCoA
CoA—SH
P i
GTP GDP
ADP
ATP
Succinate
FADFADH2
Fumarate
CitricacidcycleH2O
Malate
Oxaloacetate
NADH+H+
NAD+
1
2
3
4
5
6
7
8
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The Electron Transport
Chain
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The Electron Transport Chain
In the ETC, high-energy electrons of NADH and FADH2 are passedstep-by-step to the low energy level of oxygen through a series(chain) of electron carriers.
Each component of the chain can accept electrons from the precedingcarrier protein and transfer them to the following carrier in specificsequence.
Each carrier is capable of accepting or donating one or twoelectrons.
Oxygen is the last e- acceptor at the end of the chain.
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Oxidative Phosphorylation & The Electron Transport Chain
Oxidative phosphorylation – the process of extracting ATP from NADHand FADH2, through passage of their electrons along the ETC.
• The ½ O2 accepts the two electrons at the end of the chain and,together with 2 H+, forms water.
• NADH provides electrons, that have enough energy tophosphorylate 3 ADP to 3 ATP.
• FADH2 produces 2 ATP.
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How Many ATP:-----------------------------------------------------------------------------
Source FADH2 NADH ATP Yield----------------------------------------------------------------------------
Glycolysis 2 ATP
Glycolysis 2 NADH = 4 (6) ATP*
PyruvateAceylCoA 2 NADH = 6 ATP
Krebs Cycle 2 ATP
Krebs Cycle 6 NADH = 18 ATP
Krebs Cycle 2 FADH2 = 4 ATP
-----------------------------------------------------------------------------------------------
TOTAL 36 (38) ATP*
*NADH transport across the mitochondrial membrane requires ATP
(1 ATP per 1 NADH).
Oxidative Phosphorylation is Achieved by the
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Oxidative Phosphorylation is Achieved by theChemiosmotic Coupling Mechanism
Mitochondrion Chloroplast
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MITOCHONDRIONSTRUCTURE
Intermembranespace
MembraneElectrontransport
chain
Mitochondrion Chloroplast
CHLOROPLASTSTRUCTURE
Thylakoidspace
Stroma
ATP
Matrix
ATPsynthaseKey
H+
Diffusion
ADP + P
H+
i
Higher [H+]
Lower [H+]
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Chemiosmotic Theory
Electrons from NADH and FADH2 lose energy as they pass along the ETC in
oxidative phosphorylation. That lost energy is used to phosphorylate ADPto ATP.
Chemiosmotic theory describes how phosphorylation occurs.
• H+ accumulate in the intermembrane space.
The protein carrier complexes in the ETC act also as proton pumps.
As NADH and FADH2 move through the ETC, H+ (protons) are pumpedfrom the matrix across the cristae and into the intermembrane space.
10 protons are pumped out of the matrix for each pair of electronsmoving down the ETC.
• A pH and electrical gradient across the cristae is created.
Accumulation of H
+
creates a proton gradien (equiv. to a pH gradient)and an electric charge (or voltage) gradient. These gradients arepotential energy reserves or stored energy.
• ATP synthases generate ATP. ATP synthases (channel proteins) allowprotons to flow back into the matrix. The protons moving through thechannels generate the energy for the channel proteins to produce ATP.
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Electron Transport Chain
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Stepwise Energy Harvest via NAD+
and the Electron Transport Chain
• In glycolysis and Krebs Cycle, glucose moleculesare broken down in a series of steps.
• Electrons from some intermediate products are
transferred to NAD+, a coenzyme; hence, NAD+
is the e- acceptor.
• NADH and FADH2 account for most of theenergy extracted from food.
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• NADH, together with FADH2 passes the
electrons to the electron transport chain.• Unlike an uncontrolled reaction, the electrontransport chain passes electrons in a series ofsteps instead of one controlled, unexplosive
reaction.• Oxygen (terminal e- acceptor) pulls electrons
down the chain in an energy-yielding tumble.
• The energy yielded is used to regenerateATP.
2 H 1/ O1/2 OH
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2 H+ + 2 e –
2 H
(from food via NADH & FADH2)
Controlled
release ofenergy forsynthesis of
ATP ATP
ATP
ATP
2 H+
2 e –
H2O
+ 1/2 O21/2 O2H2 +
1/2 O2
H2O
Explosiverelease of
heat and lightenergy
Cellular respirationUncontrolled reaction
F r e e e n e r g y ,
G
F r e e e n e r g y ,
G
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The Electron Transport Chain
• In the ETC, high-energy electrons of NADH andFADH2 are passed step-by-step to the low energy
level of oxygen through a series (chain) of electroncarriers.
• Each carrier is capable of accepting or donating oneor two electrons.
The Malate-Aspartate Shuttle
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The Malate Aspartate Shuttle
Steps:
In the cytosol,NADH powers the conversion of OAA to malate.
Malate crosses to the mitochondrial matrix and powers theformation of a new NADH molecule.
Malate is converted to OAA, then to aspartate
Aspartate is transported back to the cytoplasm, where it isconverted to OAA again.
Cytosolic NADH drives the formation of a matrix NADH and the consequent oxidative phosphorylation of 3 ADPs to 3 ATPs.
The Glycerol Phosphate Shuttle for FADH
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The Glycerol Phosphate Shuttle for FADH2
Steps:
• Reduction of DHAP to G3P by cytosolic NADH.• Transport of G3P across the inner membrane to
the matrix.
• Conversion of G3P back to DHAP, resulting in
the reduction of FAD to FADH2.
Each cytosolic NADH results in the formation of 1 matrix FADH
2 , which drives the
formation of only 2 ATPs.
------------
NADH T i h Sh l ?
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NADH Transport without a Shuttle?
------------ In some plants, NADH can cross theouter mitochondrial membrane and a shuttlemechanism is not necessary.
• NADH reacts directly with ubiquinone (or CoQ)at the outer surface of the inner membrane.
• However, the step of proton pumping by FMN isbypassed, decreasing the amount of ATP that
can be generated.
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The Electron Carriers in the Krebs Cycle and ETC
NADH El t C i
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NADH as Electron Carrier
FADH El t C i
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FADH2 as Electron Carrier
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The Principal Electron Carriers in the ETC
• Flavin mononucleotide (FMN) - similar in structure to FAD,
with 1 phosphate group.- accepts 2 electrons from NADH and passes them to CoQ.
- reduced form: FMNH2, hence 2 protons are also transferred.
• Ubiquinone or coenzyme Q (CoQ) – can donate or accept 2
electrons simultaneously; can carry 2 protons in its reducedform; small molecule compared to other e- carriers.
El t C i i th ETC t’
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Electron Carriers in the ETC……. cont’n
• Cytochromes (fig. a & b) – heme proteins with Fe-containingporphyrin ring;
– They pick up electrons on their Fe atoms, which can be reversiblyreduced from Fe3+ to Fe2+.
– In their reduced forms, cyt. carry only 1 e-, without a proton.
Fe-S proteins – also involved in e- transfer.
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The Pathway of Electron Transport
• The electron transport chain is in the cristae of themitochondrion.
• Most of the chain’s components are proteins,
which exist in multiprotein complexes.• The carriers alternate reduced and oxidized states
as they accept and donate electrons.
• Electrons drop in free energy as they go down the
chain and are finally passed to O2, forming water.
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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 c 1
Cyt a
Cyt a 3
IV
10
0
Multiproteincomplexes
F r e e e n e r g y ( G ) r e l a t i v e t o O 2 ( k c a l / m o l )
H2O
O22 H+ + 1/2
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Oxidative Phosphorylation
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Mitochondrion
Glycolysis
PyruvateGlucose
Cytosol
ATP
Substrate-levelphosphorylation
ATP
Substrate-levelphosphorylation
Citricacidcycle
ATP
Oxidativephosphorylation
Oxidativephosphorylation:electron transport
andchemiosmosis
Electronscarried
via NADH
Electrons carriedvia NADH and
FADH2
Substrate-Level Phosphorylation
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Substrate Level Phosphorylation- ATP formation by enzymatic transfer of a phosphate group
from an intermediate to ADP.- synthesis of high-energy phosphate bonds through
reaction of inorganic phosphate with an activated organicsubstrate.
Enzyme
ADP
PSubstrate
Product
Enzyme
ATP
+
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Oxidative Phosphorylation
• A small amount of ATP is formed in glycolysis and thecitric acid cycle by substrate-level phosphorylation.
• ~ 90% of the ATP generated by cellular respiration isthrough oxidative phosphorylation.
• This is a process of ATP production powered by
energy derived from redox reactions of an ETC.
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During oxidative phosphorylation,
chemiosmosis couples electron transport toATP synthesis.
•
NADH and FADH2 (electron carriers) donateelectrons to the electron transport chain, whichpowers ATP synthesis via oxidativephosphorylation.
Chemiosmosis: The Energy Coupling
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Chemiosmosis: The Energy-CouplingMechanism
• Electron transfer in the electron transport chaincauses proteins to pump H+ from the mitochondrialmatrix to the intermembrane space, creating aproton gradient.
• H+ then moves back across the membrane,passing through channels in ATP synthase.
• ATP synthase uses the exergonic flow of H+ todrive phosphorylation of ATP.
• This is an example of chemiosmosis, the use ofenergy in a H+ gradient to drive cellular work.
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• The energy stored in a H+
gradient across amembrane couples the redox reactions of theelectron transport chain to ATP synthesis.
• The H+ gradient (also a pH gradient) is referred
to as a proton-motive force, emphasizing itscapacity to do work.
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Protein complexof electroncarriers
H+
ATP ATP ATP
GlycolysisOxidative
phosphorylation:electron transportand chemiosmosis
Citricacidcycle
H+
Q
IIII
II
FADFADH2
+ H+NADH NAD+
(carrying electronsfrom food)
Innermitochondrialmembrane
Innermitochondrialmembrane
Mitochondrialmatrix
Intermembranespace
H+
H+
Cyt c
IV
2H+ + 1/2 O2 H2O
ADP +
H+
ATP
ATPsynthase
Electron transport chainElectron transport and pumping of protons (H+),
Which create an H+ gradient across the membrane
P i
ChemiosmosisATP synthesis powered by the flow
of H+ back across the membrane
Oxidative phosphorylation
ATP SynthaseINTERMEMBRANE SPACE
H+ A rotor within the
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ATP SynthaseH+ H+
H+H+
H+
H+
H+
H+
ATP
MITOCHONDRAL MATRIX
ADP
+
Pi
A rotor within themembrane spinsas shown whenH+ flows pastit down the H+
gradient.
A stator anchoredin the membraneholds the knobstationary.
A rod (or ―stalk‖)extending intothe knob alsospins, activatingcatalytic sites inthe knob.
Three catalyticsites in thestationary knobjoin inorganicphosphate toADP to makeATP.
An Accounting of ATP Productionb C ll l R i i
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by Cellular Respiration
• During cellular respiration, most energy flows inthis sequence:
glucose NADH electron transport chainproton-motive force ATP
• About 40% of the energy in a glucose molecule istransferred to ATP during cellular respiration,making about 38 ATP.
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CYTOSOL Electron shuttlesspan membrane 2 NADH
or
2 FADH2
MITOCHONDRION
Oxidativephosphorylation:electron transport
andchemiosmosis
2 FADH22 NADH 6 NADH
Citricacidcycle
2AcetylCoA
2 NADH
Glycolysis
Glucose2
Pyruvate
+ 2 ATP
by substrate-levelphosphorylation
+ 2 ATP
by substrate-levelphosphorylation
+ about 32 or 34 ATP
by oxidation phosphorylation, dependingon which shuttle transports electronsform NADH in cytosol
About36 or 38 ATPMaximum per glucose:
How Many ATP?
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How Many ATP?--------------------------------------------------------------------------------------
--------
Source FADH2 NADH ATP Yield
------------------------------------------------------------------------------------------------
Glycolysis 2 ATP
Glycolysis 2 NADH = 4 (6) ATP*
PyruvateAceylCoA 2 NADH = 6 ATP
Krebs Cycle 2 ATP
Krebs Cycle 6 NADH = 18 ATP
Krebs Cycle 2 FADH2 = 4 ATP
--------------------------------------------------------------------------------------
---------TOTAL 36 (38) ATP*
*NADH transport across the mitochondrial membranerequires ATP (1 ATP per 1 NADH).
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Anaerobic Respiration
(Fermentation)
F t ti bl ll t
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Fermentation enables some cells toproduce ATP without the use of oxygen.
• Glycolysis can produce ATP with or without
O2 (i.e.,in aerobic or anaerobic conditions).• In the absence of O2, glycolysis couples with
fermentation to produce ATP.
Glucose
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Pyruvate
CYTOSOL
No O2 presentFermentation
Ethanolor
lactate
Acetyl CoA
MITOCHONDRION
O2 presentCellular respiration
Citric
acidcycle
T f F t ti
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Types of Fermentation
• Fermentation consists of glycolysis plusreactions that regenerate NAD+, which can bereused by glycolysis.
• Two common types:
--alcohol fermentation
--lactic acid fermentation
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CO2
+ 2 H+
2 NADH2 NAD+
2 Acetaldehyde
2 ATP2 ADP + 2 Pi
2 Pyruvate
2
2 Ethanol
Alcohol fermentation
Glucose Glycolysis
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+ 2 H+
2 NADH2 NAD+
2 ATP2 ADP + 2 P i
2 Pyruvate
2 Lactate
Lactic acid fermentation
Glucose Glycolysis
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• In alcohol fermentation, pyruvate is converted to
ethanol in two steps, with the first releasing CO2.
enzymes: pyruvate decarboxylase; alcoholdehydrogenase.
• In lactic acid fermentation, pyruvate is reducedto NADH, forming lactate as an end product, withno release of CO2.
enzyme: lactic acid dehygrogenase
Fermentation & Cellular Respiration
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Fermentation & Cellular RespirationCompared
• Both processes use glycolysis to oxidizeglucose and other organic fuels to pyruvate.
• The processes have different final electronacceptors:
-- organic molecule (such as pyruvate) infermentation
-- O2 in cellular respiration
• Cellular respiration produces much more ATP.
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• Yeasts and many bacteria are facultativeanaerobes, meaning that they can surviveusing either fermentation or cellular respiration.
• In a facultative anaerobe, pyruvate is a fork inthe metabolic road that leads to two alternativecatabolic routes.
Significance of Fermentation Pathway
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Significance of Fermentation Pathway
Why should the energy in the energy-rich molecule,NADH be removed and put into the formation ofethanol or lactate?
• Oxidative phosphorylation cannot accept the
electrons of NADH without oxygen.• The purpose of fermentation is to release or free
some NAD+ for glycolysis to occur
(or NAD+ would remained bottled up in NADH).
• Reward: 2 ATP from glycolysis for each 2 pyruvateconverted.
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Plant
Metabolic Pathways
The Versatility of Catabolism
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y
• Catabolic pathways funnel electrons from manykinds of organic molecules into cellular respiration.
• Glycolysis accepts a wide range of carbohydrates.
• Proteins must be digested to amino acids; amino
groups can feed glycolysis or the citric acid cycle.
• Fats are digested to glycerol (used in glycolysis)and fatty acids (used in generating acetyl CoA).
• An oxidized gram of fat produces more than twiceas much ATP as an oxidized gram ofcarbohydrate.
Proteins Carbohydrates Fats
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Citric
acidcycle
Oxidativephosphorylation
NH3
Aminoacids
Sugars
Glycolysis
Glucose
Glyceraldehyde-3- P
Pyruvate
Acetyl CoA
Fattyacids
Glycerol
Biosynthesis (Anabolic
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y (Pathways)
• The plant body uses small molecules to build
other substances.• These small molecules may come directly
from food (inorganic nutrients in plants), fromglycolysis, or from the citric acid cycle.
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Krebs Cycle is the ―Metabolic Hub‖ for the Breakdown and Synthesis of Many
Different Types of Molecules.
Regulation of Cellular Respiration
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Regulation of Cellular Respirationvia Feedback Mechanisms
• Feedback inhibition is the most commonmechanism for control.
• If ATP concentration begins to drop, respirationspeeds up; when there is plenty of ATP,respiration slows down.
• Control of catabolism is based mainly on
regulating the activity of enzymes at strategicpoints in the catabolic pathway.
Gl l i
Glucose
AMP
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Citricacidcycle
Glycolysis
Pyruvate
Acetyl CoA
Fructose-6-phosphate
Phosphofructokinase
Fructose-1,6-bisphosphate
–
Inhibits
ATP Citrate
Inhibits
Stimulates+
–