copyright © 2005 pearson education, inc. publishing as benjamin cummings chapter 9 cellular...

Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings

Chapter 9

• Cellular Respiration


Energy Transformations


Metabolism Respiration Link

• The giant panda obtains energy for its cells by eating plants


E Transformations, Thermodynamics, Ecosystems

• Energy flows into ecosystem as sunlight, and out as heat Light energy

ECOSYSTEM

CO2 + H2O

Photosynthesisin chloroplasts

Cellular respirationin mitochondria

Organicmolecules

+ O2

ATP

powers most cellular work

HeatenergyFigure 9.2



• Catabolic pathways yield Energy by oxidizing organic fuels


Oxidation, Reduction (No way to make this fun)

• Reducing agents lose electrons and are oxidized, and the oxidizing agents gains electrons and is reduced.

• The oxidizing agent removes electrons from another substance, and is thus itself reduced.

• Because it "accepts" electrons, the oxidizing agent is also called an electron acceptor.

• Oxygen is the quintessential oxidizer.


Catabolic Pathways and Production of ATP

• Breakdown of organic molecules is exergonic

Energy Released



• Cellular respiration

– Most prevalent and efficient catabolic pathway

– Consumes O2 and organic molecules e.g. glucose

– Yields ATP



Glucose is oxidized

oxygen is reduced

The Big Idea

Why We Eat and Breathe


Stepwise Energy Harvest

• Glucose oxidized in a series of steps


Electrons from Glyceraldehyde-3-Phosphate

• Electrons from organic compounds

– Usually first transferred to NAD+, a coenzyme

NAD+

H

O

O

O O–

O

O 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


Electrons from NADH

• NADH (reduced form of NAD+)

– Passes electrons to the e- transport chain


Follow the Bouncing Electrons

• e- transport chain– Passes e- in a series of steps instead of

explosive reaction– Uses E from the e- transfer to form ATP


Oxidative phosphorylation

– Driven by e- transport chain– Generates ATP


The 3 Stages of Cellular Respiration

GlycolysisCitric acid cycle (Kreb’s cycle)Oxidative phosphorylation (Electron Transport/

Chemiosmosis)


Step by Step

Glycolsis

Glucose Pyruvate

ATP

Substrate-levelphosphorylation

Mitochondrion


Step by Step

ATP


Mitochondrion

Glycolsis

Glucose Pyruvate

ATP


Citric acid cycle


Step by Step

Electronscarried

via NADH

Glycolsis

Glucose Pyruvate

ATP


Electrons carried via NADH and

FADH2

Citric acid cycle

Oxidativephosphorylation:electron transport

andchemiosmosis

ATPATP


Oxidativephosphorylation

Mitochondrion


Glycolysis

• Glycolysis harvests E by oxidizing glucose to pyruvate

• Glycolysis– Means “splitting

sugar”– Glucose pyruvate– Occurs in cytoplasm


Glycolysis

• Glycolysis: Breaks down glucose into two molecules of pyruvate

• Citric acid (Kreb’s)cycle: Completes breakdown of glucose


Glycolysis

• 2 major phases

– E investment phase

– E payoff phase

Glycolysis Citricacidcycle


ATP ATP ATP

2 ATP

4 ATP

used

formed

Glucose

2 ATP + 2 P

4 ADP + 4 P

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

2 Pyruvate + 2 H2O

Energy 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+

Figure 9.8


Dihydroxyacetonephosphate

Glyceraldehyde-3-phosphate

H H

H

HH

OHOH

HO HO

CH2OHH H

H

HO H

OHHO

OH

P

CH2O P

H

OH

HO

HO

HHO

CH2OH

P O CH2 O CH2 O P

HOH HO

HOH

OP CH2

C O

CH2OH

HCCHOHCH2

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


Citricacidcycle

Figure 9.9 A

Glycolysis: Energy Investment


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 ATP

Phosphoglycerokinase

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

Figure 9.8 B

Glycolysis: Energy Pay Off


Kreb’s Cycle

• Citric acid (or Kreb’s, or TCA) cycle completes the E-yielding oxidation of organic molecules

• Takes place in matrix of mitochondrion


Kreb’s Cycle

• Pyruvate first converted to acetyl CoA, links cycle to glycolysis

CYTOSOL MITOCHONDRION

NADH + H+NAD+

2

31

CO2 Coenzyme APyruvate

Acetyle CoA

S CoA

C

CH3

O

Transport protein

O–

O

O

C

C

CH3


Kreb’s Cycle

• Overview of citric acid cycle

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


Figure 9.11


Figure 9.12

Acetyl CoA

NADH

Oxaloacetate

CitrateMalate

Fumarate

SuccinateSuccinyl

CoA

-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 CHCOO–

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

Kreb’s Cycle: A closer Look


Oxidative phosphorylation: 3 Big Ideas

• NADH and FADH2Donate e- to e- transport chain, which powers ATP synthesis via oxidative phosphorylation

• Chemiosmosis couples e- transport to ATP synthesis

• e- from NADH and FADH2 lose E in steps


Oxidative Phosphorylation

• At end of the chain e- passed to O2, forming

water

H2O

O2

NADH

FADH2

FMN

Fe•S Fe•S

Fe•S

O

FAD

Cyt b

Cyt c1

Cyt c

Cyt a

Cyt a3

2 H + + 12

I

II

III

IV

Multiproteincomplexes

0

10

20

30

40

50

Fre

e e

ner

gy

(G)

rela

tive

to O

2 (k

cl/m

ol)


Chemiosmosis: The Energy-Coupling Mechanism

• ATP synthase– Enzyme that actually makes ATP– Energy from e- drives formation of hydrogen

concentration gradient.– Potential Energy !!!!

INTERMEMBRANE SPACE

H+

H+

H+

H+

H+

H+ H+

H+

P i

+ADP

ATP

MITOCHONDRIAL MATRIX


Chemiosmosis

• e- transfer pumps H+ f/ mitochondrial matrix to intermembrane space

INTERMEMBRANE SPACE

H+

H+

H+

H+

H+

H+ H+

H+

P i

+ADP

ATP



Chemiosmosis

• Resulting H+ gradient– Stores E– Drives chemiosmosis– Referred to as a proton-motive

force– E-coupling mechanism, drives

cellular work

INTERMEMBRANE SPACE

H+

H+

H+

H+

H+

H+ H+

H+

P i

+ADP

ATP



• Chemiosmosis and the e- transport chain

Oxidativephosphorylation.electron transportand chemiosmosis

Glycolysis

ATP ATP ATP

InnerMitochondrialmembrane

H+

H+H+

H+

H+

ATPP i

Protein complexof electron carners

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


An Accounting of ATP Production by Cellular Respiration

• 3 main processes in metabolism

Electron shuttlesspan membrane

CYTOSOL 2 NADH

2 FADH2

2 NADH 6 NADH 2 FADH22 NADH

Glycolysis

Glucose2

Pyruvate

2AcetylCoA

Citricacidcycle

Oxidativephosphorylation:electron transport

andchemiosmosis

MITOCHONDRION

by substrate-levelphosphorylation

by substrate-levelphosphorylation

by oxidative phosphorylation, dependingon which shuttle transports electronsfrom NADH in cytosol

Maximum per glucose:About

36 or 38 ATP

+ 2 ATP + 2 ATP + about 32 or 34 ATP

or

Figure 9.16


Energy Transfer not 100%

• ~ 40% of E in a glucose molecule

– Transferred to ATP during cellular respiration, making ~ 36 ATP


Fermentation

• Glycolysis

– Produces ATP w/ or w/o oxygen, aerobic or anaerobic conditions

– Glycolysis + reactions that regenerate NAD+, which can be reused by glyocolysis

– Two types alcohol and lactic acid


Fermentation

• Glycolysis + reactions that regenerate NAD+, which can be reused by glyocolysis


Fermentation

• Alcohol fermentation– Pyruvate ethanol in two steps, one of which

releases CO2


Lactic acid Fermentation

Pyruvate reduced by NADH to form lactate as a waste product (Pyruvate oxidizes NADH)

OUCH !


Fermentation - Cellular Respiration Compared

• Both use glycolysis to oxidize glucose to pyruvate

• Differ in final e- acceptor

– Aldehyde transition step in alcohol fermentation

– Pyruvate in lactic acid fermentation

• Cellular respiration produces more ATP

Tiny

Bubble


You never knew how exciting PYRUVATE was

• Pyruvate is key juncture in catabolism

Glucose

CYTOSOL

Pyruvate

No O2 presentFermentation

O2 present Cellular respiration

Ethanolor

lactate

Acetyl CoA

MITOCHONDRION

Citricacidcycle

Figure 9.18


Evolutionary Significance of Glycolysis• Glycolysis occurs in nearly all organisms

• Probably evolved before O2 in the atmosphere


Catabolism

• Catabolism of various molecules from food

Amino acids

Sugars Glycerol Fattyacids

Glycolysis

Glucose

Glyceraldehyde-3- P

Pyruvate

Acetyl CoA

NH3

Citricacidcycle


FatsProteins Carbohydrates

Figure 9.19

Beta

Oxidation

2X more

ATP


Biosynthesis (Anabolic Pathways)

• The body uses small molecules to build other substances

• Some Intermediates of glycoysis and the Kreb’s Cycle can be used to form amino acids


The control of cellular respirationGlucose

Glycolysis

Fructose-6-phosphate

Phosphofructokinase

Fructose-1,6-bisphosphateInhibits Inhibits

Pyruvate

ATPAcetyl CoA

Citricacidcycle

Citrate


Stimulates

AMP

+

– –

Figure 9.20


http://www.youtube.com/watch?feature=player_detailpage&v=Bs1f2XjCok8


http://www.youtube.com/watch?feature=player_detailpage&v=3aZrkdzrd04

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