Chapter 9 Cellular Respiration. Fig. 9-2 Light energy ECOSYSTEM Photosynthesis in chloroplasts CO 2 + H 2 O Cellular respiration in mitochondria Organic

Chapter 9Chapter 9

Cellular Respiration

Fig. 9-2

Lightenergy

ECOSYSTEM

Photosynthesis in chloroplasts

CO2 + H2O

Cellular respirationin mitochondria

Organicmolecules+ O2

ATP powers most cellular work

Heatenergy

ATP

I. Catabolic Pathways and Production of ATP

• Fermentation = partial degradation of sugars that occurs without O2

• Aerobic respiration uses organic molecules and O2 and yields ATP

• Anaerobic respiration = similar to aerobic but consumes compounds other than O2

• Cellular respiration includes aerobic and anaerobic

• C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy (ATP + heat)

II. Redox Reactions: Oxidation and Reduction

• Transfer of electrons, releases energy stored in organic molecules, used to synthesize ATP

A. Principle of Redox

• Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions

• Oxidation = substance loses electrons, oxidized

• Reduction = substance gains electrons, reduced (the amount of + charge is reduced)

• Electron donor = reducing agent

• Electron receptor = oxidizing agent

Fig. 9-UN1

becomes oxidized(loses electron)

becomes reduced(gains electron)

Fig. 9-UN2

becomes oxidized

becomes reduced

Fig. 9-3

Reactants

becomes oxidized

becomes reduced

Products

Methane(reducing

agent)

Oxygen(oxidizing

agent)

Carbon dioxide Water

Fig. 9-UN3

becomes oxidized

becomes reduced

B. NAD+ and the Electron Transport Chain

• Glucose is broken down in a series of steps

• Electrons are first transferred to NAD+, a coenzyme

• As an electron acceptor, NAD+ functions as an oxidizing agent

• Each NADH (the reduced form of NAD+) represents stored energy that is tapped to make ATP

• How NAD works

Fig. 9-4

Dehydrogenase

Reduction of NAD+

Oxidation of NADH

2 e– + 2 H+

2 e– + H+

NAD+ + 2[H]

NADH

+

H+

H+

Nicotinamide(oxidized form)

Nicotinamide(reduced form)

• NADH passes the electrons to the electron transport chain

• ETC passes electrons in a series of steps instead of one explosive reaction

• O2 pulls electrons down the chain in an energy-yielding tumble

• The energy yielded regenerates ATP

Fig. 9-5

Fre

e en

erg

y, G

Fre

e en

erg

y, G

(a) Uncontrolled reaction

H2O

H2 + 1/2 O2

Explosiverelease of

heat and lightenergy

(b) Cellular respiration

Controlledrelease ofenergy for

synthesis ofATP

2 H+ + 2 e–

2 H + 1/2 O2

(from food via NADH)

ATP

ATP

ATP

1/2 O22 H+

2 e–E

lectron

transp

ort

chain

H2O

III. Stages of Cellular Respiration: A Preview

• Cellular respiration has three stages:

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

– Citric acid cycle (completes the breakdown of glucose)

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

Fig. 9-6-1

Substrate-levelphosphorylation

ATP

Cytosol

Glucose Pyruvate

Glycolysis

Electronscarried

via NADH

Fig. 9-6-2

Mitochondrion


ATP

Cytosol

Glucose Pyruvate

Glycolysis

Electronscarried

via NADH


ATP

Electrons carriedvia NADH and

FADH2

Citricacidcycle

Fig. 9-6-3

Mitochondrion


ATP

Cytosol

Glucose Pyruvate

Glycolysis

Electronscarried

via NADH


ATP

Electrons carriedvia NADH and

FADH2

Oxidativephosphorylation

ATP

Citricacidcycle

Oxidativephosphorylation:electron transport

andchemiosmosis

• Oxidative phosphorylation (powered by redox reactions) generates most of the ATP (about 90% of total from cellular resp)

• Other 10% of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation

Fig. 9-7

Enzyme

ADP

PSubstrate

Enzyme

ATP+

Product

Concept 9.2: Glycolysis harvests chemical energy by oxidizing glucose to pyruvate

• Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate, 2 ATP and 2 NADH (high energy e- carriers)

• Glycolysis occurs in the cytoplasm and has two major phases:

– Energy investment phase

– Energy payoff phase

• How glycolysis works

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 H2O

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

ATP

ADP

Hexokinase1

ATP

ADP

Hexokinase1

Glucose

Glucose-6-phosphate

Glucose

Glucose-6-phosphate

Fig. 9-9-2

Hexokinase

ATP

ADP

1

Phosphoglucoisomerase2

Phosphogluco-isomerase

2

Glucose

Glucose-6-phosphate

Fructose-6-phosphate

Glucose-6-phosphate


1

Fig. 9-9-3

Hexokinase

ATP

ADP

Phosphoglucoisomerase

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

Glucose

ATP

ADP

Hexokinase

Glucose-6-phosphate

Phosphoglucoisomerase


ATP

ADP

Phosphofructokinase


Aldolase

Isomerase

Dihydroxyacetonephosphate

Glyceraldehyde-3-phosphate

1

2

3

4

5

Aldolase

Isomerase


Dihydroxyacetonephosphate


4

5

Fig. 9-9-52 NAD+

NADH2

+ 2 H+

2

2 P i

Triose phosphatedehydrogenase

1, 3-Bisphosphoglycerate

6

2 NAD+



NADH2

+ 2 H+

2 P i


6

2

2

Fig. 9-9-62 NAD+

NADH2


+ 2 H+

2 P i

2

2 ADP


Phosphoglycerokinase2 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

Phosphoglycerokinase


2 ATP

3-Phosphoglycerate2

Phosphoglyceromutase

2-Phosphoglycerate2

2-Phosphoglycerate2

2

Phosphoglycero-mutase

6

7

8

8

Fig. 9-9-82 NAD+

NADH2

2

2

2

2

+ 2 H+

Triose phosphatedehydrogenase2 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

Pyruvate kinase

2 Pyruvate

10

2 P i

IV. Citric acid cycle completes oxidation

• With O2, pyruvate enters mitochondrion

• Pyruvate must be converted to acetyl CoA, which links the cycle to glycolysis

Fig. 9-10

CYTOSOL MITOCHONDRION

NAD+ NADH + H+

2

1 3

Pyruvate

Transport protein

CO2Coenzyme A

Acetyl CoA

• Citric acid cycle (Krebs cycle) takes place within mito matrix

• Cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn (and 2 CO2, cutting up “sugar” even more)

Fig. 9-11

Pyruvate

NAD+

NADH

+ H+Acetyl CoA

CO2

CoA

CoA

CoA

Citricacidcycle

FADH2

FAD

CO22

3

3 NAD+

+ 3 H+

ADP + P i

ATP

NADH

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

FAD

FADH2

Fumarate

CitricacidcycleH2O

Malate

Oxaloacetate

NADH

+H+

NAD+

1

2

3

4

5

6

7

8

• Overview Glycolysis - Citric Acid Cycle

V. Electron Transport Chain

• NADH and FADH2 donate e- s to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation

• In the cristae of mitochondrion

• Carriers alternate reduced and oxidized states as they accept and donate e-

• e- s drop in free energy as they go down the chain and are passed to O2, forming H2O

Fig. 9-13

NADH

NAD+2FADH2

2 FADMultiproteincomplexesFAD

Fe•S

FMN

Fe•S

Q

Fe•S

Cyt b

Cyt c1

Cyt c

Cyt a

Cyt a3

IV

Fre

e en

erg

y (G

) r e

lat i

ve t

o O

2 (

kcal

/mo

l)

50

40

30

20

10 2

(from NADHor FADH2)

0 2 H+ + 1/2 O2

H2O

e–

e–

e–

• e- s are transferred from NADH or FADH2 to the electron transport chain

• Electron transport chain generates no ATP

• Function is to break the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts

• Electron Transport Chain and Oxi Phos (3min)

VI. Chemiosmosis: Energy-Coupling

• e- transfer in ETC causes proteins to pump H+ from mito matrix to intermembrane space

• H+ then moves back across membrane, passing through channels in ATP synthase

• ATP synthase uses the exergonic (energy releasing) flow of H+ to drive phosphorylation of ATP (ADP to ATP)

• Chemiosmosis = use of energy in a H+ gradient to drive cellular work

• H+ gradient is a proton-motive force, emphasizing its capacity to do work

Fig. 9-14

INTERMEMBRANE SPACE

Rotor

H+

Stator

Internalrod

Cata-lyticknob

ADP+P ATP

i

MITOCHONDRIAL MATRIX

Fig. 9-16

Protein complexof electroncarriers

H+

H+H+

Cyt c

Q

V

FADH2 FAD

NAD+NADH

(carrying electronsfrom food)

Electron transport chain

2 H+ + 1/2O2H2O

ADP + P i

Chemiosmosis

Oxidative phosphorylation

H+

H+

ATP synthase

ATP

21

• ETC / Oxi Phos Overview

VII. ATP Production by Cellular Respiration

• During cellular respiration, most energy flows in this sequence:

glucose NADH electron transport chain proton-motive force ATP

• About 40% of energy in a glucose molecule is transferred to ATP during cellular respiration (about 36 / 38 ATP)

Fig. 9-17

Maximum per glucose: About36 or 38 ATP

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

Oxidativephosphorylation:electron transport

andchemiosmosis

Citricacidcycle

2AcetylCoA

Glycolysis

Glucose2

Pyruvate

2 NADH 2 NADH 6 NADH 2 FADH2

2 FADH2

2 NADHCYTOSOL Electron shuttles

span membrane

or

MITOCHONDRION

• Cell Respiration Part 2 (9min)

• Cellular Respiration Overview - Bozeman (14min)

VIII. Fermentation and anaerobic respiration

• W/o O2, glycolysis couples with fermentation or anaerobic respiration to produce ATP

• Anaerobic respiration uses an electron transport chain with an electron acceptor other than O2, ex. sulfate

• Fermentation uses phosphorylation instead of an electron transport chain to generate ATP

IX. Types of Fermentation

• Fermentation = glycolysis plus reactions that regenerate NAD+ (can be reused by glycolysis)

• Alcohol fermentation = pyruvate is converted to ethanol in two steps, w/ the first releasing CO2

• Yeast = used in brewing, winemaking, and baking

Fig. 9-18a

2 ADP + 2 P i 2 ATP

Glucose Glycolysis

2 Pyruvate

2 NADH2 NAD+

+ 2 H+CO2

2 Acetaldehyde2 Ethanol

(a) Alcohol fermentation

2

• Lactic acid fermentation = pyruvate is reduced to NADH, forming lactate, w/ no release of CO2

• Some fungi and bacteria = cheese and yogurt

• Human muscle cells = generate ATP when O2 is scarce

Fig. 9-18b

Glucose

2 ADP + 2 P i 2 ATP

Glycolysis

2 NAD+ 2 NADH+ 2 H+

2 Pyruvate

2 Lactate

(b) Lactic acid fermentation

X. Fermentation and Aerobic Respiration Compared

• Both use glycolysis to oxidize glucose to pyruvate

• Have different final electron acceptors: an organic molecule (such as pyruvate or acetaldehyde) in fermentation and O2 in cellular respiration

• Cellular respiration produces 38 ATP per glucose molecule; fermentation produces 2 ATP per glucose molecule

• Obligate anaerobes = carry out fermentation or anaerobic respiration and cannot survive in the presence of O2

• Facultative anaerobes (Yeast and many bacteria) = can survive using either fermentation or cellular respiration

– Pyruvate is a fork in the metabolic road that leads to two alternative catabolic routes

Fig. 9-19Glucose

Glycolysis

Pyruvate

CYTOSOL

No O2 present:Fermentation

O2 present:

Aerobic cellular respiration

MITOCHONDRION

Acetyl CoAEthanolor

lactateCitricacidcycle

XI. Evolutionary Significance of Glycolysis

• Glycolysis occurs in nearly all organisms

• Glycolysis probably evolved in ancient prokaryotes before there was O2 in atmosphere

XII. Versatility of Catabolism

• Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration

• Glycolysis accepts a wide range of carbohydrates

• Proteins = digested to amino acids; amino groups can feed glycolysis / citric acid cycle

• Fats = digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA, by beta oxidation)

• An oxidized gram of fat produces more than 2xs as much ATP as an oxidized gram of carbohydrate

Fig. 9-20Proteins

Carbohydrates

Aminoacids

Sugars

Fats

Glycerol Fattyacids

Glycolysis

Glucose

Glyceraldehyde-3-

Pyruvate

P

NH3

Acetyl CoA

Citricacidcycle


XIII. Regulation by Feedback Mechanisms

• Feedback inhibition is most common mechanism for control

• [ATP] begins to drop, resp speeds up; when ATP increases, resp slows down

• Control of catabolism is based on regulating the activity of enzymes at points in pathway

Fig. 9-21Glucose

GlycolysisFructose-6-phosphate

Phosphofructokinase

Fructose-1,6-bisphosphateInhibits

AMP

Stimulates

Inhibits

Pyruvate

CitrateAcetyl CoA

Citricacidcycle


ATP

+

––

Documents

Chapter 9 Cellular Respiration. Fig. 9-2 Light energy ECOSYSTEM Photosynthesis in chloroplasts CO 2 + H 2 O Cellular respiration in mitochondria Organic