1. Cellular Respiration
A.P. Biology

2. powers most cellular work
Energy
Flows into an ecosystem as sunlight and 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

3. Catabolic pathways yield energy by oxidizing organic fuels
The breakdown of organic molecules is exergonic
Fermentation
Is a partial degradation of sugars that occurs without oxygen

4. Catabolic pathways yield energy by oxidizing organic fuels
Cellular respiration
Is the most prevalent and efficient catabolic pathway
Consumes oxygen and organic molecules such as glucose
Yields ATP

5. Redox Reactions: Oxidation and Reduction
Catabolic pathways yield energy
Due to the transfer of electrons
Redox reactions
Transfer electrons from one reactant to another by oxidation and reduction
Oxidation
A substance loses electrons, or is oxidized
Reduction
A substance gains electrons, or is reduced

6. becomes oxidized (loses electron)
becomes reduced (gains electron)

7. Some redox reactions Do not completely exchange electrons
Change the degree of electron sharing in covalent bonds
CH4 H C O
Methane (reducing agent)
Oxygen (oxidizing agent)
Carbon dioxide
Water +
2O2
CO2
Energy
2 H2O
becomes oxidized
becomes reduced
Reactants
Products
Figure 9.3

8. Oxidation of Organic Fuel Molecules During Cellular Respiration
Glucose is oxidized and oxygen is reduced
C6H12O6 + 6O CO2 + 6H2O + Energy
becomes oxidized
becomes reduced
G = -686 kcal/mol

9. Step by step catabolism of glucose
If electron transfer is not stepwise
A large release of energy occurs
As in the reaction of hydrogen and oxygen to form water
(a) Uncontrolled reaction
Free energy, G
H2O
Explosive release of heat and light energy
Figure 9.5 A
H2 + 1/2 O2

10. Electron transport chain (b) Cellular respiration
ETC
2 H
1/2 O2
(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
The electron transport chain
Passes electrons in a series of steps
Uses the energy from the electron transfer to form ATP

11. NAD – Nicotinamide Adenine Dinucleotide (Electron Acceptor)
Electrons from organic compounds
Are usually 1st transferred to NAD+, a coenzyme
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
Dehydragenase – removes 2 hydrogen atoms

12. NADH NADH, the reduced form of NAD+
Passes the electrons to the electron transport chain
Electrons are ultimately passed to a molecule of oxygen (Final electron acceptor)
G = -53 kcal/mol
Electron path in respiration
Food  NADH  ETC  Oxygen

14. Cellular Respiration
Respiration is a cumulative function of three metabolic stages
Glycolysis
The citric acid cycle (TCA or Krebbs)
Oxidative phosphorylation
C6H12O6 + 6O2   <---->   6 CO2 + 6 H20    + e- --->    ATP                                   DG  =  -686 Kc/mole                                263Kc  = 38%

15. Respiration Glycolysis The citric acid cycle Oxidative phosphorylation
Breaks down glucose into two molecules of pyruvate
The citric acid cycle
Completes the breakdown of glucose
Oxidative phosphorylation
Is driven by the electron transport chain
Generates ATP

16. Oxidative phosphorylation: electron transport and chemiosmosis
Respiration Overview
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
2 ATP ATP ATP

17. Substrate Level Phosphorylation
Both glycolysis and the citric acid cycle
Can generate ATP by substrate-level phosphorylation
Figure 9.7
Enzyme
ATP
ADP
Product
Substrate P +

19. Energy investment phase
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
Glycolysis
Harvests energy by oxidizing glucose to pyruvate
Glycolysis
Means “splitting of sugar”
Breaks down glucose into pyruvate
Occurs in the cytoplasm of the cell
Two major phases
Energy investment phase
Energy payoff phase

20. Energy Investment Phase

21. Energy Payoff Phase

22. Glycolysis Summary

23. The First Stage of Glycolysis
Glucose (6C) is broken down into 2 PGAL's (3C Phosphoglyceraldehyde)
This requires two ATP's

24. The Second Stage of Glycolysis
2 PGAL's (3C) are converted to 2 pyruvates
This creates 4 ATP's and 2 NADH's
The net ATP production of Glycolysis is 2 ATP's

25. Citric Acid Cycle a.k.a. Krebs Cycle
Completes the energy-yielding oxidation of organic molecules
The citric acid cycle
Takes place in the matrix of the mitochondrion

26. Krebs's Cycle (citric acid cycle, TCA cycle)
Goal: take pyruvate and put it into the Krebs's cycle, producing NADH and FADH2
Where: the mitochondria
There are two steps
The Conversion of Pyruvate to Acetyl CoA
The Kreb's Cycle proper
In the Krebs's cycle, all of Carbons, Hydrogens, and Oxygeng in pyruvate end up as CO2 and H2O
The Krebs's cycle produces 2 ATP's, 8 NADH's, and 2FADH2's per glucose molecule

27. Fate of Pyruvate

28. Carboxyl (coo-) is cleaved CO2 is released

29. Before the citric acid cycle can begin
Pyruvate must first be converted to acetyl CoA, which 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

30. 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

31. Figure 9.12 Acetyl CoA Oxaloacetate Malate Citrate Isocitrate Citric
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

32. The Kreb's Cycle 6 NADH's are generated 2 FADH2 is generated
2 ATP are generated
4 CO2's are released

33. Net Engergy Production from Aerobic Respiration
Glycolysis: 2 ATP
Kreb's Cycle: 2 ATP
Electron Transport Phosphorylation: 32 ATP
Each NADH produced in Glycolysis is worth 2 ATP (2 x 2 = 4) - the NADH is worth 3 ATP, but it costs an ATP to transport the NADH into the mitochondria, so there is a net gain of 2 ATP for each NADH produced in gylcolysis
Each NADH produced in the conversion of pyruvate to acetyl COA and Kreb's Cycle is worth 3 ATP (8 x 3 = 24)
Each FADH2 is worth 2 ATP (2 x 2 = 4)
= 32
Net Energy Production: 36 ATP

34. Energy Yields: Glucose: 686 kcal/mol ATP: 7.5 kcal/mol
7.5 x 36 = 270 kcal/mol for all ATP's produced
270 / 686 = 39% energy recovered from aerobic respiration

35. After the Krebs Cycle…
During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis
NADH and FADH2
Donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation

36. 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

37. Figure 9.13 NADH 50 40 Free energy (G) relative to O2 (kcl/mol) 30 20
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

38. The Energy-Coupling Mechanism
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

39. ETC The resulting H+ gradient
Electron transfer causes protein complexes to pump H+ from the mitochondrial matrix to the intermembrane space
The resulting H+ gradient
Stores energy
Drives chemiosmosis in ATP synthase
Is referred to as a proton-motive force

40. H+ gradient = Proton motive force
Chemiosmosis
Is an energy-coupling mechanism that uses energy in the form of a H+ gradient across a membrane to drive cellular work
H+ gradient = Proton motive force

41. Electron transport chain Oxidative phosphorylation
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

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

43. Figure 9.16 MITOCHONDRION CYTOSOL or Glycolysis Citric 2 acid Pyruvate
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

66. Anaerobic Respiration
Fermentation enables some cells to produce ATP without the use of oxygen
Glycolysis
Can produce ATP with or without oxygen, in aerobic or anaerobic conditions
Couples with fermentation to produce ATP

67. Anaerobic Respiration
Fermentation consists of
Glycolysis plus reactions that regenerate NAD+, which can be reused by glyocolysis
Alcohol fermentation
Pyruvate is converted to ethanol in two steps, one of which releases CO2
Lactic acid fermentation
Pyruvate is reduced directly to NADH to form lactate as a waste product

68. (a) Alcohol fermentation (b) Lactic acid 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

69. 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

70. Glycolysis Occurs in nearly all organisms
Probably evolved in ancient prokaryotes before there was oxygen in the atmosphere

71. Figure 9.19 Glucose NH3 Pyruvate 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

72. Fructose-1,6-bisphosphate
Cellular respiration
Is controlled by allosteric enzymes at key points in glycolysis and the citric acid cycle
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