copyright © 2005 pearson education, inc. publishing as benjamin cummings cellular respiration:...

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

Cellular Respiration:

Harvesting Chemical Energy


Contexts of Respiration

– Breathing provides for the exchange of O2 and CO2 between an organism and its environment.

CO2

CO2

O2

O2Bloodstream

Muscle cells carrying out

4. Cellular Respiration

1. Breathing: bringing air into and out of the lungs

Glucose O2

CO2 H2O ATP

Lungs 2. External respiration: Exchange of O2 & CO2 between an organism (blood) and its environment

3. Internal respiration: Exchange of O2 & CO2 between the blood & body tissues

http://www.youtube.com/watch?v=rGaP9nE8d9k

A summary of cellular respiration


Oxidation of Organic Fuel Molecules During Cellular Respiration

• Cellular respiration may be defined as “A catabolic process that produces ATP when oxygen (O2) is consumed as a reactant along with the organic fuel.”

• During cellular respiration, the fuel (such as glucose) is oxidized and oxygen is reduced:

C6H12O6 + 6O2 6CO2 + 6H2O + Energy

becomes oxidized

becomes reduced


Stepwise Energy Harvest via NAD+ and the Electron Transport Chain -1

• In cellular respiration, glucose and other organic molecules are broken down in a series of steps.

• Glucose loses electrons (i.e. it gets oxidized).

• NADH and FADH2 carry these electrons and eventually deliver them to oxygen to form water 2e- + 2H+ + ½ O2 → H2O

How would these electrons make

the trip from NADH to the oxygen?

C6H12O6 + 6O2 6CO2 + 6H2O + Energy

becomes oxidized

becomes reduced


Oxidation: Loss of electrons.

Reduction: Gain of electrons.

Redox reactions require both a donor and an acceptor of electrons.

Oxidation-Reduction Reactions


NADH + H+

My friend, oxygen, I want to give you TWO electrons so you can form water.Shall I deliver these TWO electrons in one dangerous and quick step or let them take the safe steps down?

My friend NADH, Let your electrons take the steps down. Slowly, but surely

LE 9-4

NAD+

Nicotinamide(oxidized form)

Dehydrogenase

2 e– + 2 H+

2 e– + H+

NADH H+

H+

Nicotinamide(reduced form)

+ 2[H](from food)

+

Electrons from organic compounds, such as glucose, are usually first transferred to NAD+, a coenzyme, to form NADH.

NAD+ + 2e- + 2H+ ↔ NAD+H+ + H+-

-


The Stages of Cellular Respiration: A Preview

• Cellular respiration has three stages:

– Glycolysis (breaks down glucose into two molecules of pyruvate)

– The citric acid cycle (completes the breakdown of glucose)

– Oxidative phosphorylation (accounts for most of the ATP synthesis)


A Simplified model of glycolysis

NAD NADH H

Glucose2 Pyruvate

ATP2P2 ADP

22

2

2

+

+

http://www.youtube.com/watch?v=3GTjQTqUuOw


Pyruvate

Glucose

CYTOSOL

No O2 presentFermentation

Ethanolor

lactate

Acetyl CoA

MITOCHONDRION

O2 present Cellular respiration

Citricacidcycle

CYTOSOL

Pyruvate

NAD+

MITOCHONDRION

Transport protein

NADH + H+

Coenzyme ACO2

Acetyl Co A

The Intermediate Stage Between Glycolysis and the Citric Acid Cycle


The Intermediate Stage Between Glycolysis and the Citric Acid Cycle

CO2

Pyruvate

NAD NADH H

CoA

Acetyl CoA(acetyl coenzyme A)

Coenzyme A


• The citric acid cycle, also called the Krebs cycle, takes place within the mitochondrial matrix

• The cycle oxidizes acetyl CoA (the organic fuel derived from pyruvate), generating the following per one turn of the cycle:

– 1 ATP

– 3 NADH

– 1 FADH2

– 2 CO2.

The Citric Acid Cycle


The Mitochondrion

Mitochondrion

Intermembrane space

Outer membrane

Inner membrane

Cristae

Matrix

MitochondrialDNA

Freeribosomes in themitochondrialmatrix

Mitochondrion

Glycolysis

PyruvateGlucose

Cytosol

ATP

Substrate-levelphosphorylation

ATP


Citricacidcycle

Glycolysis and the Citric Acid Cyclehttp://www.youtube.com/watch?v=-cDFYXc9Wko

Pyruvate(from glycolysis,2 molecules per glucose)

ATP ATP ATP

Glycolysis Oxidationphosphorylation

CitricacidcycleNAD+

NADH

+ H+

CO2

CoA

Acetyl CoACoA

CoA

Citricacidcycle

CO22

3 NAD+

+ 3 H+

NADH3

ATP

ADP + P i

FADH2

FAD

The Citr

ic Acid

Cycle


Cellular Respiration—Aerobic Cellular Respiration: Citric Acid Cycle

Two “turns” of the citric acid cycle produce: 2 ATP 6 NADH2 FADH2

What energy molecules are produced in breaking down one molecule of glucose in the citric acid cycle?


• One glucose molecule would yield a maximum of 32 ATP via cellular respiration.

• Glycolysis yields ___ ATP by substrate-level phosphorylation.

• The citric acid cycle yields ___ ATP by substrate-level phosphorylation.

• The rest of 32 ATP ( ____ ATP) will be formed by oxidative phosphorylation.

2- Oxidative Phosphorylation


2- Oxidative Phosphorylation

• http://www.wiley.com/legacy/college/boyer/0470003790/animations/electron_transport/electron_transport.swf

LE 9-6_3

Mitochondrion

Glycolysis

PyruvateGlucose

Cytosol

ATP


ATP


Citricacidcycle

ATP

Oxidativephosphorylation

Oxidativephosphorylation:electron transport

andchemiosmosis

Electronscarried

via NADH

Electrons carriedvia NADH and

FADH2


Oxidative Phosphorylation: 1- The Electron Transport Chain

3 4


Oxidative Phosphorylation: 1- The Electron Transport Chain

• 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.


Oxidative Phosphorylation: 1- Electron Transport Chain / Generation of Proton Motive Force

3 4


Oxidative Phosphorylation: 2- Chemiosmosis

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

Oxidative Phosphorylation (Summary): 1- The electron transport chain 2- Chemiosmosis



Matrix of the mitochondrion

Inter-membrane space


321

H2O

e-

Electrons are transferred from NADH andFADH2 through a series of electron carriers

within the cristae. O2 is the final electronacceptor.

Energy of electrons “falling” is used to moveH+ up its concentration gradient from the

matrix to the outer compartment.

ATP synthetase harnesses the kinetic energyof the H+ “falling” down its concentrationgradient to bond ADP and Pi to form ATP.

+++++++++++++++++++++++++++++++++++++++

NADH

NADH

Glycolysis

Intermediate stage

NADH

FADH2

Citricacidcycle ATP

12 O2

e-

e-

H+

H+

H+H+

H+

H+

H+H+

H+

Electron carriers

Matrix

H+ pumps

ATP synthetase

ADPPi

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.


http://www.youtube.com/watch?v=kN5MtqAB_Yc&feature=related

LE 9-16

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 26 or 28 ATP

by oxidation phosphorylation, dependingon which shuttle transports electronsform NADH in cytosol

About30 or 32 ATPMaximum per glucose:

http://www.youtube.com/watch?v=rGaP9nE8d9k

A summary of cellular respiration

copyright © 2005 pearson education, inc. publishing as benjamin cummings cellular respiration:...

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