plant cellular respiration

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.



Fig. 9-2

Lightenergy

ECOSYSTEM

Photosynthesisin chloroplasts

CO2 + H2O

Cellular respirationin mitochondria

Organicmolecules

+ O2

ATP powers most cellular work

Heatenergy

ATP



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.



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.



A General Overview of Respiration



Fig. 9-6-1

Substrate-levelphosphorylation

ATP

Cytosol

Glucose Pyruvate

Glycolysis

Electrons

carriedvia NADH



Fig. 9-6-2

Mitochondrion


ATP

Cytosol

Glucose Pyruvate

Glycolysis

Electrons

carriedvia NADH


ATP

Electrons carried

via NADH andFADH2

Citricacid

cycle



Fig. 9-6-3

Mitochondrion


ATP

Cytosol

Glucose Pyruvate

Glycolysis

Electrons

carriedvia NADH


ATP

Electrons carried

via NADH andFADH2

Oxidativephosphorylation

ATP

Citricacid

cycle

Oxidativephosphorylation:electron transport

andchemiosmosis



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.



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.



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.



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



h



Glycolysis



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).



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.



Resemblance between the Glycolytic Pathway & Calvin Cycle



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.



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



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



Fig. 9 9 1

ATP

ADP

Hexokinase

1

ATP

ADP

Hexokinase

1

Glucose

Glucose-6-phosphate

Glucose

Glucose-6-phosphate

Fig. 9-9-2



g 9 9

Hexokinase

ATP

ADP

1

Phosphoglucoisomerase

2

Phosphogluco-isomerase

2

Glucose

Glucose-6-phosphate

Fructose-6-phosphate

Glucose-6-phosphate


Fig. 9-9-3



1

g

Hexokinase

ATP

ADP


Phosphofructokinase

ATP

ADP

2

3

ATP

ADP

Phosphofructo-kinase

Fructose-1, 6-bisphosphate

Glucose

Glucose-6-phosphate



1

2

3


3

Fig. 9-9-4



g

Glucose

ATP

ADP

Hexokinase

Glucose-6-phosphate



ATP

ADP

Phosphofructokinase


Aldolase

Isomerase

Dihydroxyacetonephosphate

Glyceraldehyde-3-phosphate

1

2

3

4

5

Aldolase

Isomerase


Dihydroxyacetonephosphate


4

5

Fig. 9-9-5



g

2 NAD+

NADH2

+ 2 H+

2

2 P i

Triose phosphatedehydrogenase

1, 3-Bisphosphoglycerate

6

2 NAD+


Triose phosphate

dehydrogenaseNADH2

+ 2 H+

2 P i


6

2

2

Fig. 9-9-6



2 NAD+

NADH2


+ 2 H+

2 Pi

2

2 ADP


Phosphoglycerokinase

2 ATP

2 3-Phosphoglycerate

6

7

2

2 ADP

2 ATP


3-Phosphoglycerate

Phosphoglycero-kinase

2

7

Fig. 9-9-7



3-Phosphoglycerate


2 NAD+

2 NADH

+ 2 H+

2 P i

2

2 ADP



2 ATP

3-Phosphoglycerate2

Phosphoglyceromutase

2-Phosphoglycerate2

2-Phosphoglycerate2

2

Phosphoglycero-mutase

6

7

8

8

Fig. 9-9-8



2 NAD+

NADH2

2

2

2

2

+ 2 H+


2 P i



2 ADP

2 ATP

3-Phosphoglycerate


Enolase

2-Phosphoglycerate

2 H2O

Phosphoenolpyruvate

9

8

7

6

2 2-Phosphoglycerate

Enolase

2

2 H2O

Phosphoenolpyruvate

9

Fig. 9-9-9




2 NAD+

NADH2

2

2

2

2

2

2 ADP

2 ATP

Pyruvate

Pyruvate kinase

Phosphoenolpyruvate

Enolase2 H2O

2-Phosphoglycerate


3-Phosphoglycerate


2 ATP

2 ADP


+ 2 H+

6

7

8

9

10

2

2 ADP

2 ATP

Phosphoenolpyruvate

Pyruvatekinase

2 Pyruvate

10

2 Pi



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).



The Krebs Cycle



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



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.



CYTOSOL MITOCHONDRION

NAD+ NADH + H+

2

1 3

Pyruvate

Transport protein

CO2Coenzyme A

Acetyl CoA

Steps in the Krebs Cycle:



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



Acetyl CoA

Oxaloacetate

CoA—SH

1

Citrate

Citricacidcycle

Fig. 9-12-2



Acetyl CoA

Oxaloacetate

Citrate

CoA—SH

Citricacidcycle

1

2

H2O

Isocitrate

Fig. 9-12-3



Acetyl CoA

CoA—SH

Oxaloacetate

Citrate

H2O

Citricacidcycle

Isocitrate

1

2

3

NAD+

NADH

+ H+

-Keto-glutarate

CO2

Fig. 9-12-4



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



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



Fig. 9-12-7



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



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



The Electron Transport

Chain



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.



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.



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



Oxidative Phosphorylation is Achieved by theChemiosmotic Coupling Mechanism

Mitochondrion Chloroplast



MITOCHONDRIONSTRUCTURE

Intermembranespace

MembraneElectrontransport

chain

Mitochondrion Chloroplast

CHLOROPLASTSTRUCTURE

Thylakoidspace

Stroma

ATP

Matrix

ATPsynthaseKey

H+

Diffusion

ADP + P

H+

i

Higher [H+]

Lower [H+]



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.



Electron Transport Chain



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.



• 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



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



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



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



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 ?



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.



The Electron Carriers in the Krebs Cycle and ETC

NADH El t C i



NADH as Electron Carrier

FADH El t C i



FADH2 as Electron Carrier



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’



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.



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.



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



Oxidative Phosphorylation



Mitochondrion

Glycolysis

PyruvateGlucose

Cytosol

ATP


ATP


Citricacidcycle

ATP



andchemiosmosis

Electronscarried

via NADH

Electrons carriedvia NADH and

FADH2

Substrate-Level Phosphorylation



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

+



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.



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



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.



• 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.



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



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



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.



CYTOSOL Electron shuttlesspan membrane 2 NADH

or

2 FADH2

MITOCHONDRION


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?



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).



Anaerobic Respiration

(Fermentation)

F t ti bl ll t



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



Pyruvate

CYTOSOL

No O2 presentFermentation

Ethanolor

lactate

Acetyl CoA

MITOCHONDRION

O2 presentCellular respiration

Citric

acidcycle

T f F t ti



Types of Fermentation

• Fermentation consists of glycolysis plusreactions that regenerate NAD+, which can bereused by glycolysis.

• Two common types:

--alcohol fermentation

--lactic acid fermentation



CO2

+ 2 H+

2 NADH2 NAD+

2 Acetaldehyde

2 ATP2 ADP + 2 Pi

2 Pyruvate

2

2 Ethanol

Alcohol fermentation

Glucose Glycolysis



+ 2 H+

2 NADH2 NAD+

2 ATP2 ADP + 2 P i

2 Pyruvate

2 Lactate

Lactic acid fermentation

Glucose Glycolysis



• 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



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.



• 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



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.



Plant

Metabolic Pathways

The Versatility of Catabolism



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



Citric

acidcycle


NH3

Aminoacids

Sugars

Glycolysis

Glucose

Glyceraldehyde-3- P

Pyruvate

Acetyl CoA

Fattyacids

Glycerol

Biosynthesis (Anabolic



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.



Krebs Cycle is the ―Metabolic Hub‖ for the Breakdown and Synthesis of Many

Different Types of Molecules.

Regulation of Cellular Respiration



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



Citricacidcycle

Glycolysis

Pyruvate

Acetyl CoA


Phosphofructokinase

Fructose-1,6-bisphosphate

–

Inhibits

ATP Citrate

Inhibits

Stimulates+

–

plant cellular respiration

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