Cellular Respiration Part III:
Krebs Cycle
Figure 9.6-3
Electrons
carried
via NADH
Glycolysis
Glucose
Pyruvate
Electrons carried
via NADH and
FADH2
Citric
acid
cycle
Pyruvate
oxidation
Acetyl CoA
CYTOSOL
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
MITOCHONDRION
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
Citric Acid Cycle
(Krebs Cycle)
Curriculum Framework
3. In the Krebs cycle, carbon dioxide is released from
organic intermediates, ATP is synthesized from ADP
and inorganic phosphate via substrate level
phosphorylation, and electrons are captured by
coenzymes.
4. Electrons that are extracted in the series of Krebs
cycle reactions are carried by NADH and FADH2 to the
electron transport chain.
4
Figure 9.11
Pyruvate
CO2
NAD
CoA
NADH
+ H
Acetyl CoA
CoA
CoA
Citric
acid
cycle
2 CO2
3 NAD
FADH2
3 NADH
FAD
+ 3 H
ADP + P i
ATP
6
Krebs Cycle
• Occurs in the mitochondrial matrix
• Releases the remaining carbons from the
remnant glucose
• Transfers the energy to NAD, FAD, and ADP
7
Coenzyme A
Carbon dioxide
Electron carrier (NADH)
Carbon dioxide
ATP
Electron carrier (FADH2)
Coenzyme A
Electron carrier (NADH)
Figure 9.12-1
Acetyl CoA
CoA-SH
1
Oxaloacetate
Citrate
Citric
acid
cycle
Figure 9.12-2
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
Citric
acid
cycle
Figure 9.12-3
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD
Citric
acid
cycle
3
NADH
+ H
CO2
-Ketoglutarate
Figure 9.12-4
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD
Citric
acid
cycle
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
NAD
NADH
Succinyl
CoA
+ H
CO2
Figure 9.12-5
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD
Citric
acid
cycle
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
CoA-SH
5
NAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H
CO2
Figure 9.12-6
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Citrate
Isocitrate
NAD
Citric
acid
cycle
Fumarate
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
6
CoA-SH
5
FADH2
NAD
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H
CO2
Figure 9.12-7
Acetyl CoA
CoA-SH
H2O
1
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD
Citric
acid
cycle
7
H2O
Fumarate
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
6
CoA-SH
5
FADH2
NAD
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H
CO2
Figure 9.12-8
Acetyl CoA
CoA-SH
NADH
+ H
H2O
1
NAD
8
Oxaloacetate
2
Malate
Citrate
Isocitrate
NAD
Citric
acid
cycle
7
H2O
Fumarate
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
6
CoA-SH
5
FADH2
NAD
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
NADH
+ H
CO2
Figure 9.12a
Acetyl CoA
CoA-SH
H 2O
1
Oxaloacetate
2
Citrate
Isocitrate
Figure 9.12b
Isocitrate
NAD
NADH
3
+ H
CO2
CoA-SH
-Ketoglutarate
4
NAD
NADH
Succinyl
CoA
+ H
CO2
Figure 9.12c
Fumarate
6
CoA-SH
5
FADH2
FAD
Succinate
GTP GDP
ADP
ATP
Pi
Succinyl
CoA
Figure 9.12d
NADH
+ H
NAD
8 Oxaloacetate
Malate
H 2O
7
Fumarate
Where does each atom end up?
C6H12O6
27
So what did we get from Krebs?
• Name the energy related end products of Krebs.
• By what process is ATP formed?
• Name the waste products.
• Where do the events of Krebs occur?
• Do cells in all kingdoms go through the Krebs
cycle?
• Where are the electrons headed?
28
So, What Did We Get From Krebs?
29
Figure 9.6-3
Electrons
carried
via NADH
Glycolysis
Glucose
Pyruvate
Electrons carried
via NADH and
FADH2
Citric
acid
cycle
Pyruvate
oxidation
Acetyl CoA
CYTOSOL
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
MITOCHONDRION
ATP
ATP
ATP
Substrate-level
phosphorylation
Substrate-level
phosphorylation
Oxidative
phosphorylation
Curriculum Framework
• f. Cellular respiration in eukaryotes
involves a series of coordinated enzymecatalyzed reactions that harvest free
energy from simple carbohydrates.
31