Cellular Respiration

BIOL 101: General Biology I

Chapter 9

Rob Swatski Associate Professor of Biology

HACC – York Campus

Energy & Open

Systems Energy enters an

ecosystem as sunlight…

…and exits as heat

Photosynthesis O2 + Glucose

Cellular Respiration CO2 + ATP + heat

2

Light energy

ECOSYSTEM

Photosynthesis in chloroplasts

CO2 + H2O

Cellular respiration in mitochondria

Organic molecules

+ O2

ATP powers most cellular work

Heat energy

ATP

exergonic

endergonic

3

4

Catabolic Pathways

Anaerobic respiration (fermentation)

Partial breakdown of organics that

occurs without O2 Yields 2 ATP

Aerobic respiration

Complete breakdown of

organics with O2

Yields 36 or 38 ATP

5

C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy

6

Reduction

Oxidation

Redox Reactions

e-

is oxidized (loses e-)

becomes reduced (gains e-)

General Example of a Redox Reaction

7

is oxidized

becomes reduced

Aerobic Cellular Respiration = Redox Reaction

8

9

Electron Transfer in

Cellular Respiration

Uses the coenzyme: NAD+

NAD+ (oxidized) is both an electron

acceptor & oxidizing agent

NADH (reduced) represents stored

energy used to synthesize ATP

Dehydrogenase

e-

10

e- e-

11

Dehydrogenase

Reduction of NAD+

Oxidation of NADH

2 e– + 2 H+ 2 e– + H+

NAD+ + 2[H]

NADH

+

H+

H+

Nicotinamide (oxidized)

Nicotinamide (reduced)

12

13

Where do all the electrons

go?

Electron Transport Chain (ETC)

ETC passes e- in a series of steps

O2 pulls e- down the ETC in an

energy-yielding tumble

This energy is used to make ATP

Uncontrolled reaction

H2 + 1/2 O2

Explosive release of

heat and light energy

Cellular respiration

Controlled release of energy for

synthesis of ATP

2 H+ + 2 e–

2 H 1/2 O2

(from food via NADH)

1/2 O2

14

15

Cellular Respiration: 3 Main Stages

Glycolysis

Citric Acid Cycle (Krebs Cycle)

Oxidative phosphorylation

Substrate-level phosphorylation

ATP

Cytosol

Glucose Pyruvate

Glycolysis

Electrons carried

via NADH

16

Mitochondrion

Substrate-level phosphorylation

ATP

Cytosol

Glucose Pyruvate

Glycolysis

Electrons carried

via NADH

Substrate-level phosphorylation

ATP

Electrons carried via NADH and

FADH2

Citric acid cycle

17

Mitochondrion

Substrate-level phosphorylation

ATP

Cytosol

Glucose Pyruvate

Glycolysis

Electrons carried

via NADH

Substrate-level phosphorylation

ATP

Electrons carried via NADH and

FADH2

Oxidative phosphorylation

ATP

Citric acid cycle

Oxidative phosphorylation:

e- transport &

chemiosmosis

18

Enzyme

ADP

P

Substrate

Enzyme

ATP +

Product

Substrate-Level Phosphorylation

Used to make smaller amounts

of ATP

Uses glycolysis & citric acid cycle

19

20

Glycolysis

Occurs in cytoplasm

Glucose pyruvate

2 Major Phases

21

2 Major Phases of Glycolysis

1. Energy investment

phase

2. Energy payoff phase

Energy Investment Phase

Glucose

2 ADP + 2 P 2 ATP used

formed 4 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 H2O Glucose Net

4 ATP formed – 2 ATP used 2 ATP

2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+

22

ATP

ADP

Hexokinase

1

ATP

ADP

Hexokinase

1

Glucose

Glucose-6-phosphate

Glucose

Glucose-6-phosphate

Energy Investment Phase 23

Hexokinase

ATP

ADP

1

Phosphoglucoisomerase

2

Phosphogluco- isomerase

2

Glucose

Glucose-6-phosphate

Fructose-6-phosphate

Glucose-6-phosphate

Fructose-6-phosphate

isomer

24

1

Hexokinase

ATP

ADP

Phosphoglucoisomerase

Phosphofructokinase

ATP

ADP

2

3

ATP

ADP

Phosphofructo- kinase

Fructose- 1, 6-bisphosphate

Glucose

Glucose-6-phosphate

Fructose-6-phosphate

Fructose- 1, 6-bisphosphate

1

2

3

Fructose-6-phosphate

3

Energy Investment Phase 25

Glucose

ATP

ADP

Hexokinase

Glucose-6-phosphate

Phosphoglucoisomerase

Fructose-6-phosphate

ATP

ADP

Phosphofructokinase

Fructose- 1, 6-bisphosphate

Aldolase

Isomerase

Dihydroxyacetone phosphate

Glyceraldehyde- 3-phosphate

1

2

3

4

5

Aldolase

Isomerase

Fructose- 1, 6-bisphosphate

Dihydroxyacetone phosphate

Glyceraldehyde- 3-phosphate

4

5

26

2 NAD+

NADH 2

+ 2 H+

2

2 P i

Triose phosphate dehydrogenase

1, 3-Bisphosphoglycerate

6

2 NAD+

Glyceraldehyde- 3-phosphate

Triose phosphate dehydrogenase

NADH 2

+ 2 H+

2 P i

1, 3-Bisphosphoglycerate

6

2

2

Energy Capture Phase

e-

27

2 NAD+

NADH 2

Triose phosphate dehydrogenase

+ 2 H+

2 P i

2

2 ADP

1, 3-Bisphosphoglycerate

Phosphoglycerokinase

2 ATP

2 3-Phosphoglycerate

6

7

2 2 ADP

2 ATP

1, 3-Bisphosphoglycerate

3-Phosphoglycerate

Phosphoglycero- kinase

2

7

2 ATP

28

3-Phosphoglycerate

Triose phosphate dehydrogenase

2 NAD+

2 NADH

+ 2 H+

2 P i

2

2 ADP

Phosphoglycerokinase

1, 3-Bisphosphoglycerate

2 ATP

3-Phosphoglycerate 2

Phosphoglyceromutase

2-Phosphoglycerate 2

2-Phosphoglycerate 2

2

Phosphoglycero- mutase

6

7

8

8

29

2 NAD+

NADH 2

2

2

2

2

+ 2 H+

Triose phosphate dehydrogenase

2 P i

1, 3-Bisphosphoglycerate

Phosphoglycerokinase

2 ADP

2 ATP

3-Phosphoglycerate

Phosphoglyceromutase

Enolase

2-Phosphoglycerate

2 H2O

Phosphoenolpyruvate

9

8

7

6

2 2-Phosphoglycerate

Enolase

2

2 H2O

Phosphoenolpyruvate

9

30

Triose phosphate dehydrogenase

2 NAD+

NADH 2

2

2

2

2

2

2 ADP

2 ATP

Pyruvate

Pyruvate kinase

Phosphoenolpyruvate

Enolase 2 H2O

2-Phosphoglycerate

Phosphoglyceromutase

3-Phosphoglycerate

Phosphoglycerokinase

2 ATP

2 ADP

1, 3-Bisphosphoglycerate

+ 2 H+

6

7

8

9

10

2 2 ADP

2 ATP

Phosphoenolpyruvate

Pyruvate kinase

2 Pyruvate

10

2 P i

2 ATP

31

32

Summary of Glycolysis

• Location within cell:

• Aerobic or anaerobic:

• Initial reactant:

• Final product(s):

• Side products:

• Net yield of energy:

33

Summary of Glycolysis

• Location within cell:

• Aerobic or anaerobic:

• Initial reactant:

• Final product(s):

• Side products:

• Net yield of energy:

cytosol

anaerobic

glucose

2 pyruvate molecules

2 NADH

2 ATP (4 created; 2 invested)

34

The Fate of Pyruvate

When O2 is present, pyruvate

enters mitochondrion

Pyruvate must be converted to acetyl CoA

Transition reaction: b/w glycolysis &

citric acid cycle

CYTOSOL MITOCHONDRION

NAD+ NADH + H+

2

1 3

Pyruvate

Transport protein

CO2 Coenzyme A

Acetyl CoA

e-

Transition Between Glycolysis & the Citric Acid Cycle

35

Pyruvate

NAD+

NADH

+ H+ Acetyl CoA

CO2

CoA

CoA

CoA

Citric acid cycle

FADH2

FAD

CO2 2

3

3 NAD+

+ 3 H+

ADP + P i

ATP

NADH

36

37

Citric Acid Cycle (Krebs Cycle)

8 steps: each catalyzed by a

specific enzyme

Acetyl group (of acetyl CoA)

combines with oxaloacetate to

form citrate

The next 7 steps decompose citrate

back into oxaloacetate

NADH & FADH2 relay e- to the ETC

Acetyl CoA

Oxaloacetate

CoA—SH

1

Citrate

Citric acid cycle

38

Acetyl CoA

Oxaloacetate

Citrate

CoA—SH

Citric acid cycle

1

2

H2O

Isocitrate

39

Acetyl CoA

CoA—SH

Oxaloacetate

Citrate

H2O

Citric acid cycle

Isocitrate

1

2

3

NAD+

NADH

+ H+

-Keto- glutarate

CO2

e-

40

Acetyl CoA

CoA—SH

Oxaloacetate

Citrate

H2O

Isocitrate NAD+

NADH

+ H+ Citric acid cycle

-Keto- glutarate

CoA—SH

1

2

3

4

NAD+

NADH

+ H+ Succinyl CoA

CO2

CO2

e-

41

Acetyl CoA

CoA—SH

Oxaloacetate

Citrate

H2O

Isocitrate NAD+

NADH

+ H+

CO2

Citric acid cycle

CoA—SH

-Keto- glutarate

CO2 NAD+

NADH

+ H+ Succinyl CoA

1

2

3

4

5

CoA—SH

GTP GDP

ADP

P i Succinate

ATP ATP

42

Acetyl CoA

CoA—SH

Oxaloacetate

H2O

Citrate Isocitrate

NAD+

NADH

+ H+

CO2

Citric acid cycle

CoA—SH

-Keto- glutarate

CO2 NAD+

NADH

+ H+

CoA—SH

P

Succinyl CoA

i

GTP GDP

ADP

ATP

Succinate

FAD

FADH2

Fumarate

1

2

3

4

5

6

FAD e-

Flava Flav

43

Acetyl CoA

CoA—SH

Oxaloacetate

Citrate

H2O

Isocitrate NAD+

NADH

+ H+

CO2

-Keto- glutarate

CoA—SH

NAD+

NADH

Succinyl CoA

CoA—SH

P P

GDP GTP

ADP

ATP

Succinate

FAD

FADH2

Fumarate

Citric acid cycle

H2O

Malate

1

2

5

6

7

i

CO2

+ H+

3

4

44

Acetyl CoA

CoA—SH

Citrate

H2O

Isocitrate NAD+

NADH

+ H+

CO2

-Keto- glutarate

CoA—SH

CO2 NAD+

NADH

+ H+ Succinyl CoA

CoA—SH

P i

GTP GDP

ADP

ATP

Succinate

FAD

FADH2

Fumarate

Citric acid cycle

H2O

Malate

Oxaloacetate

NADH

+H+

NAD+

1

2

3

4

5

6

7

8

e-

45

Inputs Outputs

Acetyl CoA 2

2

2

2

6

ATP

NADH

FADH2

Oxaloacetate

Citric acid cycle

S—CoA

CH3

C O

O C COO

CH2

COO

46

47

Summary of Citric Acid (Krebs) Cycle

• Location within cell:

• Aerobic or anaerobic:

• Initial reactant:

• Final product(s):

• Side products:

• Net yield of energy:

48

• Location within cell:

• Aerobic or anaerobic:

• Initial reactant:

• Final product(s):

• Side products:

• Net yield of energy:

mitochondrion

aerobic

citric acid

oxaloacetate

NADH & FADH2 (10 e- total) 6 CO2

2 ATP (1 per turn)

Summary of Citric Acid (Krebs) Cycle

49

Electron Transport Chain

(ETC)

ETC is in cristae of mitochondria

Consists of multiprotein complexes

(cytochromes)

Proteins alternate b/w reduced & oxidized states

Electrons drop in free energy as

they travel down ETC

50

ETC and Energy

ETC does not directly generate

ATP

It divides the free energy drop into

smaller steps

Energy is released in manageable

amounts

Electrons are finally passed to O2, forming H2O

NADH

NAD+ 2

FADH2

2 FAD

Multiprotein complexes FAD

Fe•S

FMN

Fe•S

Q

Fe•S

Cyt b

Cyt c1

Cyt c

Cyt a

Cyt a3

IV

50

40

30

20

10 2

(from NADH or FADH2)

0 2 H+ + 1/2 O2

H2O

e–

e–

e–

51

NADH

NAD+ 2

FADH2

2 FAD

Multiprotein complexes FAD

Fe•S

FMN

Fe•S

Q

Fe•S

Cyt b

Cyt c1

Cyt c

Cyt a

Cyt a3

IV

50

40

30

20

10 2

(from NADH or FADH2)

0 2 H+ + 1/2 O2

H2O

e–

e–

e–

e- e-

FADH2 e- e- FAD

52

53

Chemiosmosis

Uses energy from H+ gradient to drive

cellular work

Proteins pump H+ from mitochondrial

matrix to intermembrane space

H+ then moves back across membrane,

passing through ATP synthase

Exergonic flow of H+ drives ATP

phosphorylation

Protein complex of electron carriers

H+

H+ H+

Cyt c

Q

V

FADH2 FAD

NAD+ NADH

(carrying electrons from food)

Electron transport chain

2 H+ + 1/2O2 H2O

ADP + P i

Chemiosmosis

Oxidative phosphorylation

H+

H+

ATP synthase

ATP

2 1

H+ H+

H+ H+

54

Protein complex of electron carriers

H+

H+ H+

Cyt c

Q

V

FADH2 FAD

NAD+ NADH

(carrying electrons from food)

Electron transport chain

2 H+ + 1/2O2 H2O

ADP + P i

Chemiosmosis

Oxidative phosphorylation

H+

H+

ATP synthase

ATP

2 1

ATP

H+ H+

H+ H+

H+

H+

H+

H+

H+

H+

H+ H+

H+ H+ H+

H+

H+

55

56

INTER- MEMBRANE SPACE

H+

ATP synthase

ATP ADP + P i

H+ MITO- CHONDRIAL MATRIX

Proton-Motive

Force

ATP

H+

57

58

Summary of Electron Transport Chain

• Location within cell:

• Aerobic or anaerobic:

• Side products:

• Final electron acceptor:

• Final product:

• Net yield of energy:

59

• Location within cell:

• Aerobic or anaerobic:

• Side products:

• Final electron acceptor:

• Final product:

• Net yield of energy:

mitochondrion

aerobic

12 NADH and FADH2

O2

H2O

32 ATP

Summary of Electron Transport Chain

Glucose

NADH

ETC

Proton-motive force

ATP

60

The Flow of Energy in Cellular Respiration

Maximum ATP per glucose:

About 36 or 38 ATP

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

Oxidative phosphorylation: electron transport & chemiosmosis

Citric acid cycle

2 Acetyl

CoA

Glycolysis

Glucose 2

Pyruvate

2 NADH 2 NADH 6 NADH 2 FADH2

2 FADH2

2 NADH

CYTOSOL

Electron shuttles span membrane

or

MITOCHONDRION

36 or 38 ATP

61

62

Fermentation (Anaerobic

Respiration) Glycolysis can produce ATP

with or without O2

Couples with fermentation

Alcohol fermentation

Lactic acid fermentation

63

Alcohol Fermentation

Pyruvate Ethanol

CO2 released

Yeast: brewing & baking

2 ADP + 2 P i 2 ATP

Glucose Glycolysis

2 Pyruvate

2 NADH 2 NAD+

+ 2 H+ CO2

2 Acetaldehyde 2 Ethanol

Alcohol Fermentation

2

2 ATP

64

65

Lactic Acid Fermentation

Pyruvate is reduced to

NADH

Lactate is formed as end-

product

CO2 is not released

Fungi & bacteria cheese &

yogurt

66

Glucose

2 ADP + 2 P i 2 ATP

Glycolysis

2 NAD+ 2 NADH

+ 2 H+ 2 Pyruvate

2 Lactate

Lactic Acid Fermentation

2 ATP

67

68

Comparison of Aerobic Respiration

& Fermentation

Both use glycolysis (glu pyruvate)

Have different final e- acceptors (O2 vs.

pyruvate/acetaldehyde)

Aerobic respiration produces 36 or 38 ATP

per glucose

Fermentation only produces 2 ATP per

glucose

69

Obligate anaerobes

Use fermentation or anaerobic respiration

Cannot survive in presence of O2

Facultative anaerobes

Use either fermentation or

aerobic respiration

Yeast & many bacteria

Opisthotonus. (Tetanus), c.1809 Charles Bell (1774-1842)

Clostridium tetani -obligate anaerobe

70

71

The Evolutionary Significance of Glycolysis Glycolysis occurs in nearly all organisms

- most likely evolved in ancient prokaryotes before there was O2 in the atmosphere

Glucose

Glycolysis

Pyruvate CYTOSOL

No O2 present:

Fermentation

O2 present:

Aerobic cellular

respiration

MITOCHONDRION

Acetyl CoA Ethanol or

lactate Citric acid cycle

Pyruvate is a “fork in the metabolic road”

72