biology-respiration- Chapter 8

8/8/2019 biology-respiration- Chapter 8

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CHAPTER 8CHAPTER 8

RESPIRATIONRESPIRATION


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8.1 ATP8.1 ATP (Adenosine Triphosphate)(Adenosine Triphosphate)

Immediate energy source that drivesImmediate energy source that drivesmost cellular work.most cellular work.

Cells do this work byCells do this work by energyenergy

couplingcoupling

- uses an- uses an

exergonicexergonic

process to drive anprocess to drive an endergonicendergonic one.one.


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Endergonic ReactionEndergonic Reaction - ends with- ends with netnet

gain

gain in energyin energy

Products have more energy thanProducts have more energy than

reactants, e.g., photosynthesisreactants, e.g., photosynthesis

Exergonic ReactionExergonic Reaction - ends with- ends with netnet

lossloss in energyin energy

Reactants have more energy thanReactants have more energy thanproducts, e.g., cellular respirationproducts, e.g., cellular respiration


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Structure and hydrolysis of ATPStructure and hydrolysis of ATP

ATP = Nucleotide with unstableATP = Nucleotide with unstable

phosphate bonds that cell hydrolyzesphosphate bonds that cell hydrolyzes

for energy to drive endergonicfor energy to drive endergonicreactions.reactions.

Consists of adenine, ribose, & chainConsists of adenine, ribose, & chain

of three phosphate groups.of three phosphate groups.


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Unstable bonds between phosphateUnstable bonds between phosphate

groups can be hydrolyzed in an exergonicgroups can be hydrolyzed in an exergonic

reaction.reaction.


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When terminal phosphate bond isWhen terminal phosphate bond is

hydrolyzed, a phosphate group ishydrolyzed, a phosphate group isremoved producing ADP (adenosineremoved producing ADP (adenosine

diphosphate).diphosphate).

ATP + HATP + H22OO

ADP + PADP + P iiUnder standard lab conditions, reactionUnder standard lab conditions, reaction

releases -31 kJ/mol (-7.3 kcal/mol).releases -31 kJ/mol (-7.3 kcal/mol).

In living cell, reaction releases -55In living cell, reaction releases -55kJ/mol (-13 kcal/mol) - 77% more thankJ/mol (-13 kcal/mol) - 77% more than

under standard conditions.under standard conditions.


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Terminal phosphate bonds of ATPTerminal phosphate bonds of ATP

are unstable, so:are unstable, so:

Products of hydrolysis reaction areProducts of hydrolysis reaction are

more stable than reactants.more stable than reactants.Hydrolysis of phosphate bonds isHydrolysis of phosphate bonds is

thus exergonic as system shifts to athus exergonic as system shifts to a

more stable state.more stable state.


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How ATP performs workHow ATP performs work

Exergonic hydrolysis of ATP coupledExergonic hydrolysis of ATP coupledwith endergonic processes - phosphatewith endergonic processes - phosphate

group transferred to another molecule.group transferred to another molecule.

Phosphate transfer enzymaticallyPhosphate transfer enzymaticallycontrolled.controlled.

Molecule receiving phosphateMolecule receiving phosphate

(phosphorylated/activated(phosphorylated/activatedintermediate) becomes more reactive.intermediate) becomes more reactive.


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The regeneration of ATPThe regeneration of ATP

ATP continually regenerated by cell.ATP continually regenerated by cell.

Rapid process: 10Rapid process: 1077 molecules used andmolecules used andregenerated/sec/cell).regenerated/sec/cell).

Reaction: endergonic.Reaction: endergonic.

ADP + PiADP + Pi ATPATP G = + 31 kJ/mol (+7.3 kcal/mol)G = + 31 kJ/mol (+7.3 kcal/mol)

Energy to drive endergonic regenerationEnergy to drive endergonic regenerationof ATP comes from exergonic process ofof ATP comes from exergonic process ofcellular respiration.cellular respiration.


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8.2 Aerobic Respiration8.2 Aerobic Respiration

Preview of cellular respirationPreview of cellular respiration(See Figure 9.6, Campbell, page 164)(See Figure 9.6, Campbell, page 164)

Stages of respiration:Stages of respiration:i.i. GlycolysisGlycolysis

ii.ii. Citric acid cycleCitric acid cycle

iii.iii. Electron transport chain (ETC)Electron transport chain (ETC)

iv.iv. Oxidative phosphorylation.Oxidative phosphorylation.


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GlycolysisGlycolysis - in cytoplasm.- in cytoplasm.

Glucose broken down into twoGlucose broken down into twomolecules of pyruvate.molecules of pyruvate.

Citric acid cycleCitric acid cycle - in mitochondrial- in mitochondrialmatrix.matrix.Completes breakdown of glucoseCompletes breakdown of glucose

by oxidizing a derivative of pyruvateby oxidizing a derivative of pyruvateto COto CO

22..


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Several steps in glycolysis and citricSeveral steps in glycolysis and citricacid cycle areacid cycle are redoxredox reactions -reactions -

dehydrogenase enzymes transferdehydrogenase enzymes transfer

electrons from substrates to NADelectrons from substrates to NAD++,,forming NADH.forming NADH.

NADH passes electrons to ETC.NADH passes electrons to ETC.


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Electrons then move from molecule toElectrons then move from molecule tomolecule until they combine withmolecule until they combine with

molecular Omolecular O22and Hand H++ to form water.to form water.

As they passed along chain, energyAs they passed along chain, energycarried by electrons is used tocarried by electrons is used to

synthesize ATP in mitochondrion viasynthesize ATP in mitochondrion via

oxidative phosphorylationoxidative phosphorylation..


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Inner membrane of mitochondrion isInner membrane of mitochondrion issite of electron transport chain (ETC)site of electron transport chain (ETC)

and chemiosmosisand chemiosmosis

ETC + Chemiosmosis = OxidativeETC + Chemiosmosis = OxidativePhosphorylation.Phosphorylation.Produces almost 90% of ATPProduces almost 90% of ATP

generated by respiration.generated by respiration.


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Some ATP formed directly duringSome ATP formed directly during

glycolysis and citric acid cycle byglycolysis and citric acid cycle by

substrate-level phosphorylationsubstrate-level phosphorylation.. Enzyme transfers phosphate group fromEnzyme transfers phosphate group from

an organic substrate to ADP, formingan organic substrate to ADP, forming

ATP.ATP.

Enzyme

ADP

P

Substrate

Product

Enzyme

ATP+


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For each molecule of glucoseFor each molecule of glucosedegraded to COdegraded to CO

22& H& H

22O, cell makesO, cell makes

up to 38 ATPup to 38 ATP

Each ATPEach ATP 7.3 kcal/mol of free7.3 kcal/mol of free

energy.energy.


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8.2.1 Glycolysis8.2.1 Glycolysis

Energy investment phase

Glucose

2 ATP used2 ADP + 2 P

4 ADP + 4 P 4 ATP formed

2 NAD+ + 4 e + 4 H+

Energy payoff phase

+ 2 H+2 NADH

2 Pyruvate + 2 H2O

2 Pyruvate + 2 H2O

2 ATP

2 NADH + 2 H+

Glucose

4 ATP formed 2 ATP used

2 NAD+ + 4 e + 4 H+

Net

Glycolysis Citricacidcycle

Oxidative

phosphorylation

ATPATPATP


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Glucose split into two 3C sugars.Glucose split into two 3C sugars.

Sugars oxidized and rearranged to formSugars oxidized and rearranged to formtwo molecules of pyruvate, ionized formtwo molecules of pyruvate, ionized form

of pyruvic acid.of pyruvic acid.

Two phases of glycolysis:Two phases of glycolysis:

1.1. Energy investment phaseEnergy investment phase

Cell invests ATP to provide activationCell invests ATP to provide activation

energy by phosphorylating glucose.energy by phosphorylating glucose.

Requires 2 ATP per glucose.Requires 2 ATP per glucose.


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2.2. Energy payoff phaseEnergy payoff phase

ATP produced by substrate-levelATP produced by substrate-levelphosphorylation.phosphorylation.

NADNAD++ reduced to NADH by electronsreduced to NADH by electrons

released by oxidation of glucose.released by oxidation of glucose.Net yield from glycolysis = 2 ATP and 2Net yield from glycolysis = 2 ATP and 2

NADH per glucose.NADH per glucose.

No CONo CO22 produced during glycolysis.produced during glycolysis.

Glycolysis occurs in presence/absence ofGlycolysis occurs in presence/absence of

OO22..


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Glucose

ATP

ADP

Hexokinase

ATP ATP ATP

Glycolysis Oxidation

phosphorylation

Citricacidcycle

Glucose-6-phosphate

Phosphoglucoisomerase

Phosphofructokinase

Fructose-6-phosphate

ATP

ADP

Fructose-

1, 6-bisphosphate

Aldolase

Isomerase

Dihydroxyacetone

phosphate

Glyceraldehyde-

3-phosphate

The

Glycoly

ticP

athw

ay


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2 NAD+

Triose phosphate

dehydrogenase

+ 2 H+

NADH2

1, 3-Bisphosphoglycerate

2 ADP

2 ATP

Phosphoglycerokinase

Phosphoglyceromutase

2-Phosphoglycerate

3-Phosphoglycerate

2 ADP

2 ATP

Pyruvate kinase

2 H2OEnolase

Phosphoenolpyruvate

Pyruvate


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Overall reaction showingOverall reaction showing allallreactantsreactantsand products resulting fromand products resulting from

glycolysis:glycolysis:

Glucose + 2ATP + 2PGlucose + 2ATP + 2Pii+ 4ADP + 2NAD+ 4ADP + 2NAD++

2 Pyruvate + 2ADP + 4ATP + 2NADH +2 Pyruvate + 2ADP + 4ATP + 2NADH +2H2H++ + 2H+ 2H

22OO


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Equation showingEquation showing netnetreaction ofreaction of

glycolytic pathway.glycolytic pathway.

Glucose + 2PGlucose + 2P ii + 2ADP + 2NAD+ 2ADP + 2NAD++

2 Pyruvate + 2ATP + 2NADH + 2H2 Pyruvate + 2ATP + 2NADH + 2H++ ++

2H2H22OO


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8.2.2 Pyruvate oxidation8.2.2 Pyruvate oxidation

> of original energy in glucose still> of original energy in glucose stillpresent in the 2 molecules of pyruvate.present in the 2 molecules of pyruvate.

If OIf O22is present, pyruvate entersis present, pyruvate enters

mitochondrion where oxidation to COmitochondrion where oxidation to CO22 isiscompleted.completed.

After pyruvate enters mitochondrion viaAfter pyruvate enters mitochondrion via

active transport, it is converted to acetylactive transport, it is converted to acetylcoenzyme A (coenzyme A (acetyl CoAacetyl CoA).).


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Involve multienzyme complex thatInvolve multienzyme complex that

catalyzes three reactions:catalyzes three reactions:

CYTOSOL

Pyruvate

NAD+

MITOCHONDRION

Transport protein

NADH + H+

Coenzyme ACO2Acetyl Co A


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1)1) Carboxyl group removed as COCarboxyl group removed as CO22..

2)2) Remaining 2C fragment oxidized toRemaining 2C fragment oxidized toacetateacetate. An enzyme transfers 2. An enzyme transfers 2

electrons to NADelectrons to NAD++ to form NADH.to form NADH.

3)3) Acetate combines with coenzyme A,Acetate combines with coenzyme A,forming the very reactiveforming the very reactive acetyl CoAacetyl CoA..

Acetyl CoA enters citric acid cycle forAcetyl CoA enters citric acid cycle for

further oxidation.further oxidation.


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Formation of Acetyl CoAFormation of Acetyl CoA

CC CC CC CC CC CC

CoACoACoACoA

CC CC CC CC CC CCPyruvatPyruvat

eses

CoACoACoACoA

CC CC CC CC

NANA

DD++

NANA

DD++

NANADHDH

NANADHDH

CCOO

OOCC

OO

OO

AcetylAcetylCoACoA

CC CC CC CC


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7.2. 3

The

Kre

bs/Citr

ic

7.2. 3

The

Kre

bs/Citr

ic

AcidC

ycle

AcidC

ycle

ATP ATP ATP


phosphorylation

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+


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Acetyl group of acetyl CoAAcetyl group of acetyl CoA

combines withcombines with OAAOAA, forming, formingcitratecitrate..

Citrate regenerated back to OAA.Citrate regenerated back to OAA.3 CO3 CO

22molecules released,molecules released,

including one released duringincluding one released during

conversion of pyruvate to acetylconversion of pyruvate to acetyl

CoA.CoA.


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Cycle generates one ATP per turn byCycle generates one ATP per turn bysubstrate-level phosphorylationsubstrate-level phosphorylation..

GTP is formed by substrate-levelGTP is formed by substrate-level

phosphorylation.phosphorylation.

GTP is used to synthesize an ATPGTP is used to synthesize an ATP

directly.directly.


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Most of chemical energyMost of chemical energy

transferred to NADtransferred to NAD++ and FADand FAD

during redox reactions.during redox reactions.

Reduced coenzymes NADH andReduced coenzymes NADH andFADHFADH

22then transfer high-energythen transfer high-energy

electrons to ETC.electrons to ETC.


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For every acetyl CoA, each cycleFor every acetyl CoA, each cycleproduces:produces:

i.i. 1 ATP by substrate-level1 ATP by substrate-levelphosphorylationphosphorylation

ii.ii.

3 NADH, and3 NADH, and

iii.iii. 1 FADH1 FADH22


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Pyruvate

(from glycolysis,

2 molecules per glucose)

ATP ATP ATP


phosphorylation

CitricacidcycleNAD+

NADH+ H+

CO2

CoA

Acetyl CoA

CoA

CoA

Citric

acid

cycleCO22

3 NAD+

+ 3 H+

NADH3

ATP

ADP + P i

FADH2

FAD


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Summary:Summary:

Acetyl CoA + 3 NADAcetyl CoA + 3 NAD++ + FAD + ADP + P+ FAD + ADP + Pii

+2H+2H22OO

2 CO2 CO22 + CoA-SH + 3NADH + 3H+ CoA-SH + 3NADH + 3H++ ++

FADHFADH22 + ATP+ ATP


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Link

reactions


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8.2.4 Electron transport chain8.2.4 Electron transport chain

(oxidative phosphorylation)(oxidative phosphorylation)4 out of 38 ATP are produced by4 out of 38 ATP are produced by

substrate-level phosphorylation:substrate-level phosphorylation:Glycolysis 2 ATP.Glycolysis 2 ATP.

Citric acid cycle 2 ATP.Citric acid cycle 2 ATP.


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NADH and FADHNADH and FADH22 account for theaccount for the

majority of energy extracted from food.majority of energy extracted from food.

NADH and FADHNADH and FADH22 link glycolysis andlink glycolysis and

citric acid cycle to oxidativecitric acid cycle to oxidativephosphorylation, which uses energyphosphorylation, which uses energy

released by ETC to power ATPreleased by ETC to power ATP

synthesis.synthesis.


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Pathway of Electron TransportPathway of Electron Transport

ETC is a collection of moleculesETC is a collection of molecules

embedded inembedded in cristaecristae..

Most components of ETC areMost components of ETC areproteins bound toproteins bound toprostheticprosthetic

groupsgroups..

Electrons drop in free energy as theyElectrons drop in free energy as theypass down ETC.pass down ETC.


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ATP ATP ATP

GlycolysisOxidative

phosphorylation:

electron transport

and chemiosmosis

Citricacidcycle

NADH

50

FADH2

40 FMN

FeS

I FAD

FeS II

IIIQ

FeS

Cyt b

30

20

Cyt c

Cyt c1

Cyt a

Cyt a3

IV

10

0

Multiproteincomplexes

Freeenergy

(G)re

lativetoO

2(kcal/mol )

H2O

O22 H+ + 1/2


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NADH

(reduced)

NAD

(oxidized)FADH2

(reduced)

FAD(oxidized)

CoQ

(oxidized)

CoQH2(reduced)

Cyto. Oxidase

(oxidized)

Cyto. Oxidase H2

(reduced) O2

H2O

During electron transport along ETC,During electron transport along ETC,

electron carriers alternate between reducedelectron carriers alternate between reduced

and oxidized states as they accept andand oxidized states as they accept anddonate electrons.donate electrons.


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Each component of chain becomesEach component of chain becomes

reduced when it accepts electronsreduced when it accepts electrons

from its uphill neighbor, which isfrom its uphill neighbor, which is

less electronegative.less electronegative.It then returns to its oxidized form asIt then returns to its oxidized form as

it passes electrons to its moreit passes electrons to its more

electronegative downhill neighbor.electronegative downhill neighbor.


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Last cytochrome of chain, cyt aLast cytochrome of chain, cyt a33,,

passes its electrons to oxygen, whichpasses its electrons to oxygen, whichis very electronegative.is very electronegative.

Each oxygen atom also picks up aEach oxygen atom also picks up a

pair of Hpair of H++ from aqueous solution tofrom aqueous solution toform water.form water.

For every two electron carriers (fourFor every two electron carriers (four

electrons), one Oelectrons), one O22molecule ismolecule is

reduced to two molecules of water.reduced to two molecules of water.


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Electrons carried by FADHElectrons carried by FADH22 havehave

lower free energy and are addedlower free energy and are addedat a lower energy level than thoseat a lower energy level than those

carried by NADH.carried by NADH.

ETC provides about one-thirdETC provides about one-third

less energy for ATP synthesisless energy for ATP synthesis

when electron donor is FADHwhen electron donor is FADH22rather than NADH.rather than NADH.


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FADH2NADH
http://en.wikipedia.org/wiki/Image:ETC.PNGhttp://en.wikipedia.org/wiki/Image:ETC.PNGhttp://en.wikipedia.org/wiki/Image:ETC.PNGhttp://en.wikipedia.org/wiki/Image:ETC.PNG


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ETC generates no ATP directly.ETC generates no ATP directly.Its function is to break the largeIts function is to break the large

free energy drop from food tofree energy drop from food to

oxygen into a series of smalleroxygen into a series of smaller

steps that release energy insteps that release energy in

manageable amounts.manageable amounts.


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Chemiosmosis: Energy-CouplingChemiosmosis: Energy-Coupling

MechanismMechanism

OXIDATIVE PHOSPHORYLATION: ETC &


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1.1. NADH delivers two electrons and twoNADH delivers two electrons and two

protons to the first protein complex (I)protons to the first protein complex (I)

located in cristae.located in cristae.

2.2. Energy is released as the electronsEnergy is released as the electrons

pass down the ETC (electrons movepass down the ETC (electrons move

from high energy to low energy level).from high energy to low energy level).

3.3. Energy is used to actively pump HEnergy is used to actively pump H++

across the membrane..across the membrane..

OXIDATIVE PHOSPHORYLATION: ETC &

CHEMIOSMOSIS : THE MECHANISM


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A MitochondrionA Mitochondrion

MatrixMatrix

AACellCell

One of ItsOne of ItsMitochondriMitochondri

aa

AACristaCrista

OuterOuter

& Inner& InnerMembraneMembraness

ntermembrantermembran

ee

aa bb

cc


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4. Protons move from matrix to4. Protons move from matrix to

intermembrane spaceintermembrane space

5. Protons are moved across by three (of5. Protons are moved across by three (of

the four) complexes/complex I, III and IVthe four) complexes/complex I, III and IV

6. Proton gradient provide energy for ATP6. Proton gradient provide energy for ATP

synthesis.synthesis.


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7.7. Diffusion of protons from intermembraneDiffusion of protons from intermembrane

space to the matrix of mitochondrionspace to the matrix of mitochondrion

through ATP synthase (Hthrough ATP synthase (H++ onlyonly

permeable to ATP synthase)permeable to ATP synthase)

8.8. As protons pass through it, energy isAs protons pass through it, energy is

obtained to phosphorylate ADP into ATPobtained to phosphorylate ADP into ATP

ADP + PADP + P ii ATP.ATP.


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10. FADH10. FADH2 delivers its electron via proteindelivers its electron via protein

complex II (at lower energy level).complex II (at lower energy level).

1 FADH1 FADH22PRODUCES 2 ATPPRODUCES 2 ATP

1 NADH PRODUCES 3 ATP1 NADH PRODUCES 3 ATP


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3.3. Process is done two more timeProcess is done two more time

times. Electrons are passed throughtimes. Electrons are passed throughprotein complexes III & IV, whichprotein complexes III & IV, which

transport two more Htransport two more H++ acrossacross

membrane.membrane.4.4. After passing through three proteinAfter passing through three protein

complexes, electrons combine withcomplexes, electrons combine with

one oxygen atom and two Hone oxygen atom and two H++ to formto formwater.water.

MitochondrialMitochondrial


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MitochondrialMitochondrial(1)(1)


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6.6. Cristae membrane impermeable toCristae membrane impermeable to

HH++ except through ATP synthase. Asexcept through ATP synthase. Asprotons pass through it, energy isprotons pass through it, energy is

obtained to make ATP from ADP &obtained to make ATP from ADP &

PPi..

7.7. FADHFADH2 delivers its electron viadelivers its electron via

protein complex II so, fewerprotein complex II so, fewerelectrons are passed into inter-electrons are passed into inter-

membrane space.membrane space.

8 2 5 C l l ti f T t l ATP P d ti8 2 5 C l l ti f T t l ATP P d ti


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8.2.5 Calculations of Total ATP Production8.2.5 Calculations of Total ATP Production

by Cellular Respirationby Cellular Respiration

CYTOSOL Electron shuttlesspan membrane 2 NADH

or

2 FADH2

MITOCHONDRION

Oxidative

phosphorylation:electron transportand

chemiosmosis

2 FADH22 NADH 6 NADH

Citric

acid

cycle

2

Acetyl

CoA

2 NADH

Glycolysis

Glucose2

Pyruvate

+ 2 ATP

by substrate-level

phosphorylation

+ 2 ATP

by substrate-level

phosphorylation

+ about 32 or 34 ATP

by oxidation phosphorylation, depending

on which shuttle transports electronsform NADH in cytosol

About36 or 38 ATPMaximum per glucose:

Summary ofSummary ofGl M t b liGl M t b li


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mm y fmm y fGlucose MetabolismGlucose Metabolism

(2)(2)


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Products generated when a molecule ofProducts generated when a molecule of

glucose is oxidized to 6 COglucose is oxidized to 6 CO

22 molecules:molecules:

ConversionsConversions

NADH in cytoplasm produces 2 or 3 ATPNADH in cytoplasm produces 2 or 3 ATP

by oxidative phosphorylation dependingby oxidative phosphorylation dependingon shuttle system used to transporton shuttle system used to transport

electrons from cytosol into mitochondrion:electrons from cytosol into mitochondrion:

If electrons are passed toIf electrons are passed to FADFAD, e.g., e.g.brain cells -brain cells - 2 ATP2 ATP..


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If electrons are passed toIf electrons are passed to NADNAD++,,e.g., liver cells & heart cells =e.g., liver cells & heart cells = 3ATP3ATP

In mitochondria:In mitochondria:

NADH - 3 ATPNADH - 3 ATP

FADHFADH22 2ATP 2ATP


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NADH(glycolysis)

Malate-

aspartate

NAD

NADHETC

NADH(glycolysis)

GP

FAD

FADH2ETC


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Krebs CycleKrebs Cycle

6 NADH = 6 x 3 ATP = 18 ATP6 NADH = 6 x 3 ATP = 18 ATP2 FADH2 = 2 x 2 ATP = 4 ATP2 FADH2 = 2 x 2 ATP = 4 ATP

Substrate-level phosphorylation = 2Substrate-level phosphorylation = 2

ATPATP

Total YieldTotal Yield

Glycolysis = 2 ATPGlycolysis = 2 ATPAerobic respiration = 34 or 36 ATPAerobic respiration = 34 or 36 ATP


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5.5. SummarySummary

PathwayPathway Substrate-levelSubstrate-levelphosphorylatiophosphorylationn

OxidativeOxidativephosphorylationphosphorylation

TotalTotalATPATP

GlycolysisGlycolysis 2 ATP2 ATP 2 NADH = 4 - 62 NADH = 4 - 6

ATPATP

6 - 86 - 8

Acetyl CoAAcetyl CoA 2 NADH = 6 ATP2 NADH = 6 ATP 66

Krebs cycleKrebs cycle 2 ATP2 ATP 6 NADH = 18 ATP6 NADH = 18 ATP

2 FADH2 = 4 ATP2 FADH2 = 4 ATP

2424

TotalTotal 4 ATP4 ATP 32 34 ATP32 34 ATP 36-3836-38


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Energy Harvested from GlucoseEnergy Harvested from Glucose

ytoplasm)ytoplasm) GlucoseGlucose

2 NADH2 NADH

2 NADH2 NADH6 NADH6 NADH2 FADH2 FADH22

2 Pyruvates2 Pyruvates

2 CO2 CO22

4 CO4 CO22

22ATPATP

44ATPATP

itochondrialitochondrialMatrix)Matrix)

(Inner(Innerembrane)embrane)

22ATPATP

3232ATPATP

ElectronElectronTransportTransportSystemSystem

GlycolysiGlycolysiss

KrebsKrebsCycleCycle

WaterWater

OxygenOxygen


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Efficiency of respirationEfficiency of respiration

Complete oxidation of glucose =Complete oxidation of glucose = 686686

kcal/mol.kcal/mol.

Phosphorylation of ADP to form ATP =Phosphorylation of ADP to form ATP = 7.37.3

kcal/mol.kcal/mol.

Efficiency of respirationEfficiency of respiration

== 7.3 kcal/mol x 38 ATP/glucose x 100%7.3 kcal/mol x 38 ATP/glucose x 100%

686 kcal/mol glucose686 kcal/mol glucose

= 40%.= 40%.


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60% energy from glucose lost60% energy from glucose lost

as heat.as heat.Some used to maintain bodySome used to maintain bodytemperature (37C).temperature (37C).

Efficient in energy conversion.Efficient in energy conversion.

8 3 A bi i ti8 3 A bi i ti


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8.3 Anaerobic respiration8.3 Anaerobic respiration

Qxidative phosphorylation ceasesQxidative phosphorylation ceasesin absence of Oin absence of O

22..

Some cells oxidize organic fuelSome cells oxidize organic fuel

and generate ATP without use ofand generate ATP without use of

OO22through fermentation.through fermentation.

E.g., anaerobic catabolism ofE.g., anaerobic catabolism ofsugars.sugars.


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Fermentation generate ATP fromFermentation generate ATP fromglucose by substrate-levelglucose by substrate-level

phosphorylation as long as there isphosphorylation as long as there is

NADNAD++

to accept electrons.to accept electrons.If NADIf NAD++ pool is exhausted,pool is exhausted,

glycolysis shuts down.glycolysis shuts down.


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Under aerobic conditions, NADHUnder aerobic conditions, NADH

transfers electrons to ETC, andtransfers electrons to ETC, andrecycles NADrecycles NAD++..

Anaerobic - ATP generated byAnaerobic - ATP generated byglycolysis; NADglycolysis; NAD++ recycled byrecycled by

transferring electrons from NADHtransferring electrons from NADH

to pyruvate/derivatives of pyruvate.to pyruvate/derivatives of pyruvate.

8.3.1 Ethanol Fermentation8.3.1 Ethanol Fermentation


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8.3.1 Ethanol Fermentation

CO2+ 2 H+

2 NADH2 NAD+

2 Acetaldehyde

2 ATP2 ADP + 2 Pi

2 Pyruvate

2

2 Ethanol

Alcohol (ethanol) fermentation

Glucose Glycolysis


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Two steps:Two steps:

1.1. Pyruvate converted toPyruvate converted to

acetaldehyde (2C), by removal ofacetaldehyde (2C), by removal of

COCO22..

2.2. Acetaldehyde reduced by NADHAcetaldehyde reduced by NADH

to ethanol.to ethanol.

Alcohol fermentation by yeast -Alcohol fermentation by yeast -brewing and winemaking.brewing and winemaking.

8 3 2 Lactic Fermentation8 3 2 Lactic Fermentation


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8.3.2 Lactic Fermentation8.3.2 Lactic Fermentation

+ 2 H+2 NADH2 NAD+

2 ATP2 ADP + 2 P i

2 Pyruvate

2 Lactate

Lactic acid fermentation

Glucose Glycolysis


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Pyruvate reduced by NADH to lactatePyruvate reduced by NADH to lactate

without release of COwithout release of CO22..Lactic acid fermentation by fungi andLactic acid fermentation by fungi and

bacteria - cheese and yogurt.bacteria - cheese and yogurt.

Human muscle cells switch from aerobicHuman muscle cells switch from aerobicrespiration to lactic acid fermentation torespiration to lactic acid fermentation to

generate ATP when Ogenerate ATP when O22 is scarce.is scarce.

Waste product, lactate, causes muscleWaste product, lactate, causes musclefatigue - converted back to pyruvate infatigue - converted back to pyruvate in

liver.liver.

GLUCOSE (6C)


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GLUCOSE (6C)

2PYRUVATES (3C)

2LACTATE (3C)

2NAD+

2NADH

+ 2H+

2NAD+

2NADH

+ 2H+

CO2

2ETHANAL /

ASETALDEHYDE (2C)

2ETHANOL (2C)

2Pyruvates converted into

2ethanol (2C) &2CO2

2NADH are used

2 ATP are produced

Yeast cell

2Pyruvates converted into

2lactate (3C)2NADH are used

2 ATP are produced

muscle cell/bacteria 2ATP


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Fermentation and Cellular RespirationFermentation and Cellular Respiration

ComparedCompared

SimilaritiesSimilarities both use both use

1.1. GlycolysisGlycolysis : oxidize sugars to pyruvate: oxidize sugars to pyruvate- 2 ATP produced by substrate-level- 2 ATP produced by substrate-level


2.2. NADNAD++

: oxidizing agent - accept: oxidizing agent - acceptelectrons from food during glycolysis.electrons from food during glycolysis.

DiffDiff


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DifferenceDifference

1.1. Mechanism for oxidizing NADH to NADMechanism for oxidizing NADH to NAD++..

Fermentation - electrons of NADHFermentation - electrons of NADHpassed to anpassed to an organic moleculeorganic molecule toto

regenerate NADregenerate NAD++..

Respiration - electrons of NADH passedRespiration - electrons of NADH passedtoto OO

22, generating ATP by oxidative, generating ATP by oxidative


2.2. ATP generated per molecule of glucose.ATP generated per molecule of glucose. Aerobic :Aerobic : 36 - 3836 - 38 ATP.ATP.

Anaerobic :Anaerobic : 22 ATP.ATP.


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Facultative AnaerobesFacultative Anaerobes

Makes ATP aerobically if OMakes ATP aerobically if O22isis

present; switch to fermentation inpresent; switch to fermentation inabsence of Oabsence of O

22..

E.g., yeast, many bacteria & humanE.g., yeast, many bacteria & human

muscle cells (cellular level).muscle cells (cellular level).

Glucose


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Pyruvate

CYTOSOL

No O2 present

Fermentation

Ethanol

or

lactate

Acetyl CoA

MITOCHONDRION

O2 present

Cellular respiration

Citric

acidcycle

8.4 Metabolism of Fat and Protein8.4 Metabolism of Fat and Protein


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Citricacidcycle

Oxidativephosphorylation

Proteins

NH3

Aminoacids

Sugars

Carbohydrates

Glycolysis

Glucose

Glyceraldehyde-3-P

Pyruvate

Acetyl CoA

Fatty

acids

Glycerol

Fats

CatabolismCatabolism


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CatabolismCatabolism

Carbohydrates:Carbohydrates:PolysaccharidesPolysaccharides

(starch/glycogen) hydrolyzed to(starch/glycogen) hydrolyzed to

glucose monomers that enterglucose monomers that enterglycolysis.glycolysis.

Hexose sugars (galactose andHexose sugars (galactose and

fructose) - modified to undergofructose) - modified to undergo

glycolysis.glycolysis.

Protein:Protein:


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Protein:Protein:

Proteins digested to individual aminoProteins digested to individual amino

acids.acids.

Amino groups removed viaAmino groups removed via

deaminationdeamination..

Nitrogenous waste excreted asNitrogenous waste excreted as

ammonia, urea, or another wasteammonia, urea, or another waste

product.product.

Carbon skeletons modified by enzymesCarbon skeletons modified by enzymes

and enter as intermediaries intoand enter as intermediaries into

glycolysis or citric acid cycle.glycolysis or citric acid cycle.

Fats:Fats:


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Fats:Fats:

Fats digested to glycerol and fattyFats digested to glycerol and fatty

acids.acids.

Glycerol converted to G3P Glycerol converted to G3P

enters glycolysis.enters glycolysis.Fatty acids split into 2C fragmentsFatty acids split into 2C fragments

viavia beta oxidationbeta oxidation..

Enter citric acid cycle as acetylEnter citric acid cycle as acetylCoA.CoA.

Bi th i (A b li P th )Bi th i (A b li P th )


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Biosynthesis (Anabolic Pathways)Biosynthesis (Anabolic Pathways)

Intermediaries in glycolysis and citric acidIntermediaries in glycolysis and citric acid

cycle can be diverted to anaboliccycle can be diverted to anabolic

pathways.pathways.

E.g., human cell synthesizes 10 differentE.g., human cell synthesizes 10 different

amino acids by modifying compoundsamino acids by modifying compounds

from citric acid cycle.from citric acid cycle.

Glucose synthesized from pyruvate.Glucose synthesized from pyruvate.

Fatty acids from acetyl CoA.Fatty acids from acetyl CoA.


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Glycolysis and citric acid cycleGlycolysis and citric acid cycle

function as metabolic interchangesfunction as metabolic interchangesthat enable cells to convert one kindthat enable cells to convert one kind

of molecule to another.of molecule to another.

E.g., conversion of excess proteinsE.g., conversion of excess proteins

and carbohydrates to fats throughand carbohydrates to fats through

intermediaries of glycolysis and citricintermediaries of glycolysis and citricacid cycle.acid cycle.

biology-respiration- Chapter 8

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