1. Chapter 9
Cellular Respiration

2. Living cells require transfusions of energy:
From outside sources
To perform their many tasks

3. powers most cellular work
Energy
Flows into an ecosystem as sunlight
Leaves as heat
Light energy
ECOSYSTEM
CO2 + H2O
Photosynthesis in chloroplasts
Cellular respiration in mitochondria
Organic molecules
+ O2
ATP
powers most cellular work
Heat energy
Figure 9.2

4. Catabolic Pathways and Production of ATP
Yield energy by:
Oxidizing organic fuels
The breakdown of organic molecules is:
Exergonic
One catabolic process is called fermentation:
It is a partial degradation of sugars
It occurs without oxygen

5. Cellular respiration:
The most prevalent and efficient catabolic pathway
It consumes:
Oxygen
Organic molecules e.g. glucose
It yields:
ATP
To keep working, cells must regenerate:

6. Redox Reactions: Oxidation and Reduction
Catabolic pathways yield energy due to:
Transfer of electrons
Redox reactions involves:
Transfer is from one reactant to another
Results in both oxidation and reduction

7. In oxidation In reduction A substance loses electrons
The substance is said to be oxidized
In reduction
A substance gains electrons
The substance is said to be reduced

8. Examples of redox reactions
Na Cl Na Cl–
becomes oxidized (loses electron)
becomes reduced (gains electron)

9. Oxidation of Organic Fuel Molecules During Cellular Respiration
Glucose is oxidized and oxygen is reduced
C6H12O6 + 6O CO2 + 6H2O + Energy
becomes oxidized
becomes reduced

10. Stepwise Energy Harvest via NAD+ and the Electron Transport Chain
Cellular respiration
Oxidation of glucose in a series of steps
Electrons from organic compounds are first:
Transferred to NAD+,
NAD+ (nicotineamide dinucleotide):
is a coenzyme

11. Cellular Respiration Why carbohydrates and fat are high energy food?
NAD+ H O O– P
CH2 HO OH N+ C
NH2 N
Nicotinamide (oxidized form) +
2[H]
(from food)
Dehydrogenase
Reduction of NAD+
Oxidation of NADH
2 e– + 2 H+
2 e– + H+
NADH
Nicotinamide (reduced form)
Figure 9.4

12. NADH: Is the reduced form of NAD+ It passes the electrons to:
The electron transport chain

13. (a) Uncontrolled reaction
If electron transfer is not stepwise:
A large release of energy occurs (explosion)
(a) Uncontrolled reaction
Free energy, G
H2O
Explosive release of heat and light energy
Figure 9.5 A
H2 + 1/2 O2

14. The electron transport chain:
Passes electrons in a series of steps
Passage is not in one explosive reaction
Energy from the electron transfer is used to:
Generate ATP

15. Electron transport chain (b) Cellular respiration
(from food via NADH)
2 H e–
2 H+
2 e–
H2O
Controlled release of energy for synthesis of ATP
ATP
Electron transport chain
Free energy, G
(b) Cellular respiration +
Figure 9.5 B

16. The Stages of Cellular Respiration: A Preview
Cellular respiration is:
A cumulative function of three metabolic stages:
Glycolysis
The citric acid cycle
Oxidative phosphorylation

17. Glycolysis means “splitting of sugar”
It Occurs in the cytosol of the cell
It harvests energy by oxidizing glucose to pyruvate
Does not require oxygen
Its end products:
Two molecules of pyruvate
Two ATP molecules
Two NADH

18. Oxidative phosphorylation: electron transport and chemiosmosis
An overview of cellular respiration
Figure 9.6
Electrons
carried
via NADH
Glycolsis
Glucose
Pyruvate
ATP
Substrate-level
phosphorylation
Electrons carried
via NADH and
FADH2
Citric acid cycle
Oxidative phosphorylation: electron transport and chemiosmosis
Oxidative
Mitochondrion
Cytosol

19. Both glycolysis and the citric acid cycle can generate ATP by:
Substrate-level phosphorylation
Figure 9.7
Enzyme
ATP
ADP
Product
Substrate P +

20. Energy investment phase
Glycolysis consists of two major phases
Energy investment phase
Energy payoff phase
A total of 4 ATP molecules
are produced
Two ATP molecules are
used
The net number of ATP
molecules is two
Glycolysis
Citric acid cycle
Oxidative phosphorylation
ATP
2 ATP
4 ATP
used
formed
Glucose
2 ATP + 2 P
4 ADP + 4
2 NAD+ + 4 e- + 4 H +
2 NADH
+ 2 H+
2 Pyruvate + 2 H2O
Energy investment phase
Energy payoff phase
4 ATP formed – 2 ATP used
2 NAD+ + 4 e– + 4 H +
Figure 9.8

21. Phosphoglucoisomerase
A closer look at the energy investment phase
Dihydroxyacetone
phosphate
Glyceraldehyde-
3-phosphate H OH HO
CH2OH O P
CH2O
CH2 C
CHOH
ATP
ADP
Hexokinase
Glucose
Glucose-6-phosphate
Fructose-6-phosphate
Phosphoglucoisomerase
Phosphofructokinase
Fructose-
1, 6-bisphosphate
Aldolase
Isomerase
Glycolysis 1 2 3 4 5
Oxidative
phosphorylation
Citric
acid
cycle
Figure 9.9 A

22. 1, 3-Bisphosphoglycerate
A closer look at the energy payoff phase
2 NAD+
NADH 2
+ 2 H+
Triose phosphate
dehydrogenase
P i P C
CHOH O
CH2 O–
1, 3-Bisphosphoglycerate
2 ADP
2 ATP
Phosphoglycerokinase
3-Phosphoglycerate
Phosphoglyceromutase
CH2OH H
2-Phosphoglycerate
2 H2O
Enolase
Phosphoenolpyruvate
Pyruvate kinase
CH3 6 8 7 9 10
Pyruvate
Figure 9.8 B

23. Takes place in the matrix of the mitochondrion Requires oxygen
The Citric Acid Cycle
Takes place in the matrix of the mitochondrion
Requires oxygen
At the end of the cycle:
Glucose breakdown is completed
All the original carbon in the original glucose molecule has been lost as CO2
The two acetyl CoA that entered the cycle produce a total of:
Two ATP (by substrate level phosphorylation)
Six NADH
Two FADH2

24. Before the citric acid cycle can begin
Pyruvate must first be converted “oxidized” to:
Acetyl CoA
Acetyl CoA links the cycle to glycolysis
CYTOSOL
MITOCHONDRION
NADH
+ H+
NAD+ 2 3 1
CO2
Coenzyme A
Pyruvate
Acetyle CoA S
CoA C
CH3 O
Transport protein O–
Figure 9.10

25. Oxidative phosphorylation
An overview of the citric acid cycle
ATP
2 CO2
3 NAD+
3 NADH
+ 3 H+
ADP + P i
FAD
FADH2
Citric acid cycle
CoA
Acetyle CoA
NADH
CO2
Pyruvate (from glycolysis, 2 molecules per glucose)
Glycolysis
Oxidative phosphorylation
Figure 9.11

26. A closer look at the citric acid cycle
Acetyl CoA
NADH
Oxaloacetate
Citrate
Malate
Fumarate
Succinate
Succinyl
CoA
a-Ketoglutarate
Isocitrate
Citric
acid
cycle S SH
FADH2
FAD
GTP
GDP
NAD+
ADP
P i
CO2
H2O
+ H+ C
CH3 O
COO–
CH2 HO HC CH 1 2 3 4 5 6 7 8
Glycolysis
Oxidative
phosphorylation
ATP
Figure 9.12
Figure 9.12

27. Oxidative Phosphorylation
Driven by the electron transport chain
Electrons (generated during glycolys & citric acid cycle) are escorted & donated by:
NaDH
FADH2
Released energy during electron transfer is used thru chemiosmosis to generates ATP

28. The Pathway of Electron Transport
In the electron transport chain
Electrons from NADH and FADH2 lose energy in several steps
At the end of the chain
Electrons are passed to oxygen, forming water
H2O O2
NADH
FADH2
FMN
Fe•S O
FAD
Cyt b
Cyt c1
Cyt c
Cyt a
Cyt a3
2 H + + 12 I II
III IV
Multiprotein complexes 10 20 30 40 50
Free energy (G) relative to O2 (kcl/mol)
Figure 9.13

29. Chemiosmosis Is an energy-coupling mechanism
It uses energy in the form of a H+ gradient across a membrane to drive ATP synhesis

30. Chemiosmosis: The Energy-Coupling Mechanism
ATP synthase
Is the enzyme that actually makes ATP
INTERMEMBRANE SPACE H+
P i +
ADP
ATP
A rotor within the membrane spins clockwise when H+ flows past it down the H+ gradient.
A stator anchored in the membrane holds the knob stationary.
A rod (for “stalk”) extending into the knob also spins, activating catalytic sites in the knob.
Three catalytic sites in the stationary knob join inorganic
Phosphate to ADP to make ATP.
MITOCHONDRIAL MATRIX
Figure 9.14

31. Figure 9.15 ATP synthase Protein complex of electron carriers
Cyt c IV Q
III I II
2 H+ + ½ O2
H2O
FADH2
FAD
NADH
NAD+
Figure 9.15 Chemiosmosis couples the electron transport chain to ATP synthesis
ADP + P
ATP i
(carrying
electrons
from
food) H+
Electron transport chain
Chemiosmosis 1 2
Oxidative phosphorylation

32. Figure 9.15a 1 H+ H+ H+ Cyt c Cyt c IV Q III I II 2 H+ + ½ O2 H2O FAD
Protein
complex
of electron
carriers H+
Cyt c
Cyt c IV Q
III I II
2 H+ + ½ O2
H2O
FADH2
FAD
Figure 9.15a Chemiosmosis couples the electron transport chain to ATP synthesis (part 1: electron transport chain)
NAD+
NADH
(carrying
electrons
from
food) 1
Electron transport chain

33. Figure 9.15b 2 H+ ADP + ATP H+ P ATP synthase i Chemiosmosis
Figure 9.15b Chemiosmosis couples the electron transport chain to ATP synthesis (part 2: chemiosmosis)
ADP + P
ATP i H+
Chemiosmosis 2

34. Figure 9.14 INTERMEMBRANE SPACE Stator H+ Rotor Internal rod Catalytic
knob
Figure 9.14 ATP synthase, a molecular mill
ADP + P i
ATP
MITOCHONDRIAL
MATRIX

35. At certain steps along the electron transport chain:
Chemiosmosis
At certain steps along the electron transport chain:
The electron transfer causes protein complexes to pump H+
Hydrogrn ions (H+) are pumped from the mitochondrial matrix to the intermembrane space
This creates a H+ gradient (stored energy) that drives ATP synthase to make ATP from:
ADP, and
inorganic phosphate

36. Electron transport chain Oxidative phosphorylation
Chemiosmosis and the electron transport chain
Oxidative
phosphorylation.
electron transport
and chemiosmosis
Glycolysis
ATP
Inner
Mitochondrial
membrane H+
P i
Protein complex
of electron
carners
Cyt c I II
III IV
(Carrying electrons
from, food)
NADH+
FADH2
NAD+
FAD+
2 H+ + 1/2 O2
H2O
ADP +
Electron transport chain
Electron transport and pumping of protons (H+),
which create an H+ gradient across the membrane
Chemiosmosis
ATP synthesis powered by the flow
Of H+ back across the membrane
synthase Q
Oxidative phosphorylation
Intermembrane
space
mitochondrial
matrix
Figure 9.15

37. An Accounting of ATP Production by Cellular Respiration
During respiration, most energy flows in this sequence:
Glucose NADH electron transport chain proton-motive force ATP

38. There are three main processes in this metabolic enterprise
Electron shuttles
span membrane
CYTOSOL
2 NADH
2 FADH2
6 NADH
Glycolysis
Glucose 2
Pyruvate
Acetyl
CoA
Citric
acid
cycle
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
MITOCHONDRION
by substrate-level
phosphorylation
by oxidative phosphorylation, depending
on which shuttle transports electrons
from NADH in cytosol
Maximum per glucose:
About
36 or 38 ATP
+ 2 ATP
+ about 32 or 34 ATP or
Figure 9.16

39. During cellular respiration:
About 40% of the energy in a glucose molecule is transferred to ATP
This result in making ATP:
2 (net) ATP (from glycolysis, by substrate- level phosphorylation)
2 ATP (from citric acid cycle; by substrate- level phosphorylation)
32-34 ATP (from electron transfer chain; by oxidative phosphorylation

40. In the absence of oxygen:
Fermentation
Fermentation:
Enables some cells to produce ATP without the use of oxygen
Cellular respiration
Relies on oxygen to produce ATP
In the absence of oxygen:
Cells can still produce ATP through a process called fermentation

41. Glycolysis vs Fermentation
Can produce ATP in the presence or absence of oxygen, i.e. in aerobic or anaerobic conditions

42. Types of Fermentation Fermentation: Types: Consists of:
Glycolysis, plus reactions that regenerate NAD+, which can be reused by glyocolysis
Types:
Alcohol fermentation:
Pyruvate is converted (in two steps):
1st to acetaldehyde and CO2
Then, to ethanol
Lactic acid fermentation:
Pyruvate is reduced directly to NADH to form lactate as a waste product

43. (a) Alcohol fermentation (b) Lactic acid fermentation
Types of Fermentation
2 ADP + 2 P1
2 ATP
Glycolysis
Glucose
2 NAD+
2 NADH
2 Pyruvate
2 Acetaldehyde
2 Ethanol
(a) Alcohol fermentation
2 Lactate
(b) Lactic acid fermentation H OH
CH3 C
O – O O–
CO2 2
Figure 9.17

44. Fermentation and Cellular Respiration Compared
Both use glycolysis to oxidize glucose and other organic fuels to pyruvate
Both differ in their final electron acceptor
Cellular respiration produces more ATP

45. Pyruvate is a key juncture in catabolism
Glucose
CYTOSOL
Pyruvate
No O2 present
Fermentation
O2 present
Cellular respiration
Ethanol or
lactate
Acetyl CoA
MITOCHONDRION
Citric
acid
cycle
Figure 9.18

46. The Versatility of Catabolism
Glycolysis and the citric acid cycle connect to many other metabolic pathways
Catabolic pathways
Funnel electrons from many kinds of organic molecules into cellular respiration

47. The catabolism of various molecules from food
Amino
acids
Sugars
Glycerol
Fatty
Glycolysis
Glucose
Glyceraldehyde-3- P
Pyruvate
Acetyl CoA
NH3
Citric
acid
cycle
Oxidative
phosphorylation
Fats
Proteins
Carbohydrates
Figure 9.19

48. Biosynthesis (Anabolic Pathways)
The body
Uses small molecules to build other substances
These small molecules may come:
Directly from food,
Through:
Glycolysis
The citric acid cycle

49. Regulation of Cellular Respiration via Feedback Mechanisms
Is controlled by allosteric enzymes at key points in glycolysis and the citric acid cycle

50. Fructose-1,6-bisphosphate
The control of cellular respiration
Glucose
Glycolysis
Fructose-6-phosphate
Phosphofructokinase
Fructose-1,6-bisphosphate
Inhibits
Pyruvate
ATP
Acetyl CoA
Citric
acid
cycle
Citrate
Oxidative
phosphorylation
Stimulates
AMP + –
Figure 9.20