Chapter 9 (Part 1): Chapter 9 (Part 1): Cellular RespirationCellular Respiration

AP BiologyMs. Gaynor

Energy Flows into ecosystems as sunlight and leaves as heat

Light energy

ECOSYSTEM

CO2 + H2O

Photosynthesisin chloroplasts

Cellular respirationin mitochondria

Organicmolecules

+ O2

ATP

powers most cellular work

Heatenergy http://wps.aw.com/bc_campbell_biology_7/

Carbon Cycle

Reminder…. AnabolicAnabolic pathways pathways (“(“A” A” for add together)for add together)

BuildBuild molecules from simpler ones (ex: molecules from simpler ones (ex: photosynthesis)photosynthesis)

Consume energy Consume energy ((endergonic)endergonic) CatabolicCatabolic pathways ( pathways (““C” C” for cut in parts)for cut in parts)

Break downBreak down complex molecules into complex molecules into simpler compounds (ex: cell respiration)simpler compounds (ex: cell respiration)

Release energy Release energy ((exergonic)exergonic)

Cellular respirationCellular respiration

Most efficient catabolic pathwayConsumes O2 and organic molecules (ex: glucose)

Yields ATP To keep working To keep working cells must regenerate ATPcells must regenerate ATP

Catabolic pathways yield energy by oxidizing organic fuels

The breakdown of organic molecules is exergonic

One catabolic process, fermentationfermentationIs a partial degradation of sugars that occurs without oxygen

Another example is cellular respirationcellular respiration

Cellular respirationCellular respirationOccurs in mitochondria

similar to combustion of gas in an engine after O2 is mixed with hydrocarbon fuel.Food = fuel for respiration. The exhaust =CO2 and H2O.

The overall process is:organic compounds + Oorganic compounds + O2 2 CO CO22 + H + H22O + energyO + energy

(ATP + heat)(ATP + heat)

Carbohydrates, fats, and proteins can all be used as the fuel, but most useful is glucose.

Mitochondria Mitochondria • # of mito’s in a cell varies by organism & tissue type

•has its own independent DNA (and ribosomes) this DNA shows similarity to bacterial DNA

•according to the endosymbiotic theory mitochondria (and chloroplasts) are descended from free-living prokaryotes.

Mitochondrion Structure

Mitochondrion Structure Outer membrane – similar to plasma

membrane; contains integral proteins Inner membrane- NOT permeable to

ions (needs help to cross); there is a membrane potential across the inner membrane; contains ATP synthase

Cristae – large surface area due to folding Matrix - gel-like in middle or lumen; many

contains enzymes for cellular respiration

RECALL…Redox ReactionsRECALL…Redox ReactionsCatabolic pathways yield energy

Due to the transfer of electrons Redox reactionsRedox reactions

Transfer e-’s from one reactant to another by oxidation and reduction In In ooxidationxidation

Substance lSubstance looses e-s (it’s oxidized)ses e-s (it’s oxidized) In In rreductioneduction

Substance Substance rreceives e-s eceives e-s (it’s reduced)(it’s reduced)

Examples of redox reactionsExamples of redox reactions

Na + Cl Na+ + Cl–

becomes oxidized(loses electron)

becomes reduced(gains electron)

Xe- + Y X + Ye-

**energy must be added to remove **energy must be added to remove e-e-

X = e- donor = X = e- donor = reducing agentreducing agent and reduces Y.and reduces Y.Y = e- recipient = Y = e- recipient = oxidizing agentoxidizing agent and oxidizes X.and oxidizes X.

Oxidation of Organic Fuel Molecules During Cellular Respiration

During cellular respirationGlucose is oxidized oxygen is reducedE-’s lose potential energy energy is released

CC66HH1212OO66 + 6 + 6OO22 6 6COCO22 + 6 + 6HH22OO + Energy + Energybecomes oxidizedbecomes oxidized

becomes reducedbecomes reduced

http://student.ccbcmd.edu/~gkaiser/biotutorials/cellresp/ets_flash.html

Electrons are not transferred directly to oxygen but are passed first to a coenzyme called NAD+ or FADNAD+ or FAD

NAD+

HO

OO O–

OO O–

O

O

O

P

P

CH2

CH2

HO OHH

HHO OH

HO

H

H

N+

C NH2

HN

H

NH2

N

N

Nicotinamide(oxidized form)

NH2+ 2[H]

(from food)

Dehydrogenase

Reduction of NAD+

Oxidation of NADH

2 e– + 2 H+

2 e– + H+

NADH

OH H

N

C +

Nicotinamide(reduced form)

N

Figure 9.4

NAD+ and FADNAD+ and FAD= = e- acceptor and e- acceptor and oxidating agentoxidating agent

2 H 1/2 O2

(from food via NADH)(from food via NADH)

2 H+ + 2 e–

2 H+

2 e–

H2O

1/2 O2

Controlled Controlled release of energy release of energy

for for synthesis ofsynthesis of

ATPATP ATP

ATP

ATP

Electro

n tran

spo

rt chain

Fre

e en

ergy

, G

(b) Cellular respiration

+

Electron Flow =food NADH/FADH2 ETC oxygen

The Stages of Cellular Respiration

Respiration is a cumulative process of 3 metabolic stages

1. Glycolysis2. The citric acid cycle3. Oxidative phosphorylation

The 3 StagesThe 3 Stages GlycolysisGlycolysis

Breaks down glucose into 2 molecules of pyruvate

Makes NADH Kreb’s Cycle (Citric acid cycle)Kreb’s Cycle (Citric acid cycle)

Completes the breakdown of glucoseMakes NADH and FADH2

Oxidative phosphorylationOxidative phosphorylationDriven by the electron transport chainGenerates ATP

An overview of cellular respiration

Figure 9.6

ElectronsElectronscarriedcarried

via NADHvia NADH

GlycolsisGlycolsisGlucoseGlucose 2 Pyruvate2 Pyruvate

ATP

Substrate-levelphosphorylation

Electrons carried Electrons carried via NADH and via NADH and

FADHFADH22

Citric Citric acid acid cyclecycle

OxidativeOxidativephosphorylation:phosphorylation:

electron electron transport andtransport and

chemiosmosischemiosmosis

ATPATP

Substrate-levelphosphorylation

Oxidativephosphorylation

Mitochondrion MatrixMitochondrion MatrixCytoplasmCytoplasm

Inner Mitochondrion Membrane Inner Mitochondrion Membrane (Cristae)(Cristae)

Both glycolysis and the citric acid cycleCan generate ATP by substrate-level

phosphorylation (not using ATP synthase!)

Figure 9.7

Enzyme Enzyme

ATP

ADP

Product

SubstrateP

+

Stage #1: GlycolysisStage #1: Glycolysis Glycolysis produces energy by oxidizing

glucose pyruvate Glycolysis

Means “splitting of sugar”Breaks down glucose into pyruvateOccurs in the cytoplasmcytoplasm of the cell

1 glucose breaks down 4 ATP made + 2 pyruvate molecules

(net gain of 2 ATP…NOT 4 ATP)

Glycolysis consists of two major phases1. Energy

investment phase (endergonic= uses 2 ATP)

2. Energy payoff phase

(exogonic = makes 4 ATP)

Glycolysis Citricacidcycle

Oxidativephosphorylation

ATP ATP ATP

2 ATP

4 ATP

used

formed

1 Glucose

2 ADP + 2 P

4 ADP + 4 P

2 NAD2 NAD++ + 4 + 4 ee-- + 4 H + 4 H ++

2 NADH

+ 2 H+

2 Pyruvate + 2 H2 Pyruvate + 2 H22OO

Energy investment phaseEnergy investment phase

Energy payoff phase

Glucose 2 Pyruvate + 2 H2O

4 ATP formed – 2 ATP used 2 ATP

2 NAD+ + 4 e– + 4 H + 2 NADH

+ 2 H+

Glycolysis

NETNET Glucose Glucose 2 pyruvate (pyruvic 2 pyruvate (pyruvic acid) acid) + 2 H+ 2 H22OO

4 ATP formed – 2 ATP used 4 ATP formed – 2 ATP used 2 ATP 2 ATP GAINGAINsubstrate-level phosphorylation usedsubstrate-level phosphorylation used

2 NAD+ + 4e- + 4H+ 2 NAD+ + 4e- + 4H+ 2 NADH + 2H+ 2 NADH + 2H+

**Glycolysis can proceed WITHOUT O**Glycolysis can proceed WITHOUT O22

The energy investment & The energy investment & Payoff phases of Payoff phases of

GlycolysisGlycolysisLet’s take a closer look….

Page 166-167 in textbook10 steps in glycolysis occuring in 2 phases

Dihydroxyacetonephosphate

Glyceraldehyde-3-phosphate

H H

H

HH

OH

OH

HOHO

CH2OH

H H

H

HO H

OHHO

OH

P

CH2O P

H

OH

HO

HO

HHO

CH2OH

P O CH2 O CH2 O P

HO

HHO

HOH

OP CH2

C O

CH2OH

H

C

CHOH

CH2

O

O P

ATP

ADPHexokinase

Glucose

Glucose-6-phosphate

Fructose-6-phosphate

ATP

ADP

Phosphoglucoisomerase

Phosphofructokinase

Fructose-1, 6-bisphosphate

Aldolase

Isomerase

Glycolysis

1

2

3

4

5

CH2OH

Oxidativephosphorylation

Citricacidcycle

Phase #1: The

Investment Phase of

Glycolysis

(endergonic)

2 NAD+

NADH2

+ 2 H+

Triose phosphatedehydrogenase

2 P i

2P C

CHOH

O

P

O

CH2 O

2 O–

1, 3-Bisphosphoglycerate2 ADP

2 ATPPhosphoglycerokinase (PFK)

CH2 O P

2

C

CHOH

3-Phosphoglycerate

Phosphoglyceromutase

O–

C

C

CH2OH

H O P

2-Phosphoglycerate

2 H2O

2 O–

Enolase

C

C

O

PO

CH2

Phosphoenolpyruvate2 ADP

2 ATP

Pyruvate kinase

O–

C

C

O

O

CH3

2

6

8

7

9

10

Pyruvate

O

Phase #2: The Payoff Phase of

Glycolysis (exogonic)

Phosphofructoskinase (PFK)

• is an allosteric enzyme

•ATP acts as an allosteric inhibitor to PFK

•High [ATP] stops glycolysis via inhibition (blocks active site)

Glycolysis http://www.sumanasinc.com/webcontent/animations/content/cellular

respiration.html

http://highered.mheducation.com/sites/0072507470/student_view0/chapter25/animation__how_glycolysis_works.html

http://www.northland.cc.mn.us/biology/Biology1111/animations/glycolysis.html

http://www.science.smith.edu/departments/Biology/Bio231/glycolysis.html

Stage #2: The Kreb’s Cycle

The citric acid cycleTakes place in the matrix of the

mitochondrion

**NEEDS O2 TO PROCEED (unlike glycolysis)

Stage #1 ½ : The Citric Acid Cycle Before the citric acid cycle can begin

Pyruvate must first be converted to acetyl CoA, which links the citric acid cycle to glycolysis

CYTOSOL MITOCHONDRION

NADH + H+NAD+

2

31

CO2

Coenzyme Coenzyme A A

(a vitamin)(a vitamin)Pyruvate

Acetyle Acetyle CoACoA

S CoA

C

CH3

O

Transport Transport proteinprotein

O–

O

O

C

C

CH3

Figure 9.10

Uses active

transport

Diffuses out of cell

Acetyl group= unstable

The Kreb’s Cycle

Also called the “Tricarboxylic Acid Cycle” or the “Citric Acid cycle”

NAD+ and FAD (both are coenzymes) = electron “carriers”; proton acceptorsThey are reduced and carry e-’s from

Citric cycle to ETCDehydrogenase catalyzes hydrogen

transfer reaction

NAD+ and FADOxidized Form Reduced Form NAD+ NADH (2 e-, 1 H)

FAD FADH2 (4 e-, 2 H)

THINK: FADH2 come into play in the 2nd stage of cellular respiration; it is also the 2nd electron carrier

An overview An overview of the citric of the citric acid cycleacid cycle

(this occurs (this occurs for EACH for EACH pyruvate pyruvate molecule)molecule)

ATP

2 CO2

3 NAD+

3 NADH+ 3 H+

ADP + P i

FAD

FADH2

Citricacidcycle

CoA

CoA Acetyle CoA

NADH+ 3 H+

CoA

CO2

Pyruvate (from glycolysis,2 molecules per glucose)

ATP ATP ATP

Glycolysis Citricacidcycle

Oxidativephosphorylation

Figure 9.11

The Kreb’s CycleThe Kreb’s CycleLet’s take a closer look….

Page 169 in textbook8 steps in citric cycle in MATRIX1 turn of cycle 2 reduced carbons enter 2 oxidized carbons leave

Figure 9.12

Acetyl CoA

NADH

Oxaloacetate

CitrateMalate

Fumarate

Succinate

SuccinylCoA

-Ketoglutarate

Isocitrate

Citricacidcycle

S CoA

CoA SH

NADH

NADH

FADH2

FAD

GTP GDP

NAD+

ADP

P i

NAD+

CO2

CO2

CoA SH

CoA SH

CoAS

H2O

+ H+

+ H+ H2O

C

CH3

O

O C COO–

CH2

COO–

COO–

CH2

HO C COO–

CH2

COO–

COO–

COO–

CH2

HC COO–

HO CH

COO–

CH

CH2

COO–

HO

COO–

CH

HC

COO–

COO–

CH2

CH2

COO–

COO–

CH2

CH2

C O

COO–

CH2

CH2

C O

COO–

1

2

3

4

5

6

7

8

Glycolysis Oxidativephosphorylation

NAD+

+ H+

ATP

Citricacidcycle

Figure 9.12

Kreb’s Cycle Summary pyruvate Acetyl-CoA + 1 NADH Each turn of cycle uses 1 pyruvate

So… 1 glucose molecule produces 2 turns of Kreb’s cycle

1 turn of cycle yields 4 NADH, 1 ATP, and 1 FADH2 and 3 CO2 (as waste product) Remember to multiply by 2…why?

http://www.sumanasinc.com/webcontent/animations/content/cellularrespiration.html

Http://highered.mheducation.com/sites/0072507470/student_view0/chapter25/animation__how_the_krebs_cycle_works__quiz_1_.html

Stage #3: Oxidative Phosphorylation

(Electron Transport Chain (ETC) + Chemiosmosis) Chemiosmosis couples electron

transport to ATP synthesis NADH and FADH2

Donate e-s to ETC, which powers ATP synthesis using oxidative phosphorylation

**OCUURS IN CRISTAE (folds of inner membrane)

What is “oxidative phosphorylation”?

Recall…Take H+/e-s away, molecule = “oxidized” Give H+/e-s, molecule = “reduced” Give phosphate, molecule =

“phosphorylated” So…oxidative phosphorylation =

process that couples removal of H+’s/ e-’s from one molecule & giving phosphate molecules to another molecule

The Pathway of Electron Transport

In the ETC…e-s from NADH and FADH2 lose energy in several steps

**NEEDS O2 TO PROCEED

(unlike glycolysis)

ETC Characteristics

Lots of proteins (cytochromes) in cristae increases surface area1000’s (many) copies of ETC

ETC carries e-’s from NADH/FADH2 O2

O2 = pulls e-s “down” ETC due to electronegativity (high affinity for e-s)

Chemiosmosis and the electron transport chain

Oxidativephosphorylation.electron transportand chemiosmosis

Glycolysis

ATP ATP ATP

InnerMitochondrialmembrane

H+

H+

H+

H+

H+

ATPP i

Protein complexof electron carriers

Cyt c

I

II

III

IV

(Carrying electronsfrom, food)

NADH+

FADH2

NAD+

FAD+ 2 H+ + 1/2 O2

H2O

ADP +

Electron transport chainElectron transport and pumping of protons (H+),

which create an H+ gradient across the membrane

ChemiosmosisATP synthesis powered by the flowOf H+ back across the membrane

ATPsynthase

Q

Oxidative phosphorylation

Intermembranespace

Innermitochondrialmembrane

Mitochondrialmatrix

Figure 9.15

http://highered.mcgraw-hill.com/olcweb/cgi/pluginpop.cgi?it=swf::535::535::/sites/dl/free/0072437316/120071/bio11.swf::Electron%20Transport%20System%20and%20ATP%20Synthesis

Protin motive force

is used!

At the end of the chainElectrons are passed to oxygen, forming waterO2 = final e- acceptor

NAD delivers e- higher than FAD NAD provides 50% more ATP

What happens at the end of the ETC chain?

ETC is a Proton (H+) Pump Uses the energy from “falling” e-s

(exergonic flow) to pump H+’s from matrix to outer compartment

A H+ (proton) gradient forms inside mitochondria

ETC does NOT make ATP directly but provides stage for CHEMIOSOMOSIS to occur

RECALL…ChemiosmosisRECALL…Chemiosmosis Is an energy-coupling mechanism that uses energy in the

form of a H+ gradient across a membrane to drive cellular work

Uses ATP synthaseMakes ~90% of ATP in Cell Resp. Proposed by Peter Mitchell (1961)

Chemiosmosis: The Energy-Coupling Mechanism

ATP synthase Is the enzyme

that actually makes ATP

INTERMEMBRANE SPACE

H+

H+

H+

H+

H+

H+ H+

H+

P i

+ADP

ATP

A rotor within the membrane spins clockwise whenH+ flows past it down the H+

gradient.

A protein anchoredin the membraneholds the knobstationary.

A rod (or “stalk”)extending into the rotor/ knob alsospins, activatingcatalytic sites inthe knob.

Three catalytic sites in the stationary knobjoin inorganic Phosphate to ADPto make ATP.

MITOCHONDRIAL MATRIXFigure 9.14

http://www.sigmaaldrich.com/life-science/metabolomics/learning-center/metabolic-pathways/atp-synthase.html

A Comparison of Chemiosmosis in Chloroplasts and Mitochondria

Chloroplasts and mitochondriaGenerate ATP by the SAME basic

mechanism: chemiosmosisBut use different sources of energy to

accomplish this http://student.ccbcmd.edu/~gkaiser/biotutorials/cellresp/

atpase_flash.html

The spatial organization of chemiosmosisDiffers in chloroplasts

and mitochondria In both organelles

electron transport chains generate a H+ gradient across a membrane

ATP synthase Uses this proton-motive

force to make ATP

At certain steps along the ETCElectron transfer causes protein complexes

to pump H+ from the mitochondrial matrix intermembrane spaceInside (matrix) = low [H+]Outside = high [H+]

The resulting H+ gradient…Stores energyDrives chemiosmosis in ATP

synthaseIs referred to as a proton-motive force

There are three main processes in this metabolic enterprise

Electron shuttlesspan membrane

CYTOSOL 2 NADH

2 FADH2

2 NADH 6 NADH 2 FADH22 NADH

Glycolysis

Glucose

2Pyruvate

2AcetylCoA

Citricacidcycle

Oxidativephosphorylation:electron transport

andchemiosmosis

MITOCHONDRION

by substrate-levelphosphorylation

by substrate-levelphosphorylation

by oxidative phosphorylation

Maximum per Maximum per glucose:glucose:

AboutAbout36 or 38 ATP36 or 38 ATP

+ 2 ATP + about 32 or 34 ATP

or

Figure 9.16

+ 2 ATP

About 40% of the energy in a glucose moleculeIs transferred to ATP during cellular respiration, making ~36- 38 ATP

http://www.sumanasinc.com/webcontent/animations/content/cellularrespiration.html

Overall (Aerobic Respiration) FADH

2NADH CO2 ATP Total ATP

Gained

Glycolysis2 4 2 (net)

PyruvatePyruvate Acetyl- Acetyl-

CoACoA

2

Kreb’sCycle

2 6 6 2 2

ETC~32-34

ATP GRAND TOTAL = ~36-38 ATP per 1 GLUCOSEATP GRAND TOTAL = ~36-38 ATP per 1 GLUCOSE

Chapter 9 (Part 2): Chapter 9 (Part 2): FermentationFermentation

AP BiologyMs. Gaynor

Fermentation Fermentation enables some cells to

produce ATP without the use of oxygen (O2)

Cellular respirationRelies on oxygen to produce ATP

In the absence of oxygenCells can still produce ATP

through fermentation

GlycolysisCan produce ATP with or without oxygen, in aerobic or anaerobic conditions

Couples with fermentation to produce ATP

Types of Fermentation

Fermentation consists ofGlycolysis plus reactions that regenerate NAD+, which can be reused by glyocolysis

Alcohol Fermentation

Pyruvate is converted to ethanol (ethyl alcohol) in two steps, one of which releases CO2

Ex: bacteria and yeast

In alcohol fermentationPyruvate is converted to ethanol (ethyl alcohol) in two steps, one of which releases CO2

GLUCOSE Pyruvate Ethanol and CO2

Ex: bacteria and yeast do this

2 ADP + 2 P1 2 ATP

GlycolysisGlucose

2 NAD+ 2 NADH

2 Pyruvate

2 Acetaldehyde (gets reduced by NADH. It is the

oxidizing agent.)

2 Ethanol(a) Alcohol fermentation

H

H OH

CH3

C

O –

OC

C O

CH3

H

C O

CH3

CO22

Lactic Acid FermentationDuring lactic acid fermentation

Pyruvate is reduced directly to NADH to form lactate as a waste product

NO CO2 is releasedEx #1: fungus and bacteria in dairy industry to make cheese/ yogurtEx #2: Human muscle cells

2 ADP + 2 P1 2 ATP

GlycolysisGlucose

2 NAD+ 2 NADH2 Pyruvate

2 Acetaldehyde (gets reduced by NADH. It

is the oxidizing agent.)

2 Ethanol

(a) Alcohol fermentation

2 ADP + 2 P1 2 ATP

GlycolysisGlucose

2 NAD+ 2 NADH

2 Lactate

(b) Lactic acid fermentation

H

H OH

CH3

C

O –

OC

C O

CH3

H

C O

CH3

O–

C O

C O

CH3O

C O

C OHH

CH3

CO22

NO CO2

made 2 Pyruvate (gets reduced by NADH. It

is the oxidizing agent.)

Fermentation and Cellular Respiration Compared

Both fermentation and cellular respirationUse glycolysis to oxidize glucose and

other organic fuels to pyruvate

Fermentation and cellular respirationDiffer in their final electron acceptor

Cell respriraition uses O2

Fermentation uses NAD+ Cellular respiration

Produces more ATP (~36-38 ATP) Fermentation

Produces 2 ATP per cycle

Pyruvate is a key juncture in catabolismGlucose

CYTOSOL

PyruvateNo O2 presentFermentation

OO22 present present

Cellular respirationCellular respiration

Ethanolor

lactate

Acetyl CoA

MITOCHONDRION

Citricacidcycle

Figure 9.18

The Evolutionary Significance of Glycolysis

GlycolysisOccurs in nearly all organismsProbably evolved in ancient prokaryotes

before there was oxygen in the atmosphereO2 in air ~2.7 bya; oldest prokaryotes ~3.5 byaAlso does not require organelles

The catabolism of various molecules from food called “intermediates”

Amino acids

Sugars Glycerol Fattyacids

Glycolysis

Glucose

Glyceraldehyde-3- P

Pyruvate

Acetyl CoA

NH3

Citricacidcycle

Oxidativephosphorylation

FatsProteins Carbohydrates

Figure 9.19

The control of cellular respiration through feedback inhibition PFK is an allosteric

enzyme

Glucose

Glycolysis

Fructose-6-phosphate

Phosphofructokinase

Fructose-1,6-bisphosphateInhibits Inhibits

Pyruvate

ATPAcetyl CoA

Citricacidcycle

Citrate

Oxidativephosphorylation

Stimulates

AMP

+

– –

Figure 9.20

Excellent Overall Tutorial of Cell Respiration

http://www.wiley.com/college/pratt/0471393878/student/animations/citric_acid_cycle/index.html