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Fig. 9-1
Chapter 9 Cellular Respiration: Harvesting Chemical Energy
Chapter 9 Cellular Respiration: Harvesting Chemical Energy
• Cellular respiration includes both aerobic and anaerobic respiration but is often used to refer to aerobic respiration
• Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose:
C6H12O6 + 6 O2 6 CO2 + 6 H2O + Energy (ATP + heat)
– Redox Reactions
Fig. 9-UN4
Dehydrogenase
Electrons from organic compounds are usually first transferred to NAD+, a coenzyme As an electron acceptor
Each NADH (the reduced form of NAD+) represents stored energy that is tapped to synthesize ATP
Fig. 9-4 NAD+ as an electron shuttle 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)
Nicotinamide adenine dinucleotide, a derivative of the vitamin niacin
NADH passes the electrons to the electron transport chain
Fig. 9-2
Lightenergy
ECOSYSTEM
Photosynthesis in chloroplasts
CO2 + H2O
Cellular respirationin mitochondria
Organicmolecules+ O2
ATP powers most cellular work
Heatenergy
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
The Stages of Cellular Respiration: A Preview
• Cellular respiration has three stages:
– Glycolysis (breaks down glucose into two molecules of pyruvate)
– The 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
I. Glycolysis
Electronscarried
via NADH
Cellular respiration has three stages:
Fig. 9-6-2
Mitochondrion
Substrate-levelphosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electronscarried
via NADH
Substrate-levelphosphorylation
ATP
Electrons carriedvia NADH and
FADH2
II.Citricacidcycle
Fig. 9-6-3
Mitochondrion
Substrate-levelphosphorylation
ATP
Cytosol
Glucose Pyruvate
Glycolysis
Electronscarried
via NADH
Substrate-levelphosphorylation
ATP
Electrons carriedvia NADH and
FADH2
Oxidativephosphorylation
ATP
Citricacidcycle
III. Oxidativephosphorylation:electron transport
andchemiosmosis
•The process that generates most of the ATP is called oxidative phosphorylation
• because it is powered by redox reactions
• Oxidative phosphorylation:
– accounts for almost 90% of the ATP generated by cellular respiration
• substrate-level phosphorylation
– A smaller amount of ATP is formed in glycolysis and the citric acid cycle by
ATP
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
• Glycolysis occurs in the cytoplasm and has two major phases:
– Energy investment phase
– Energy payoff phase
Fig. 9-8
Energy investment phase
Glucose
2 ADP + 2 P2 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
Fructose-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
Fructose-6-phosphate
Fructose-1, 6-bisphosphate
1
2
3
Fructose-6-phosphate
3
Fig. 9-9-4
Glucose
ATP
ADP
Hexokinase
Glucose-6-phosphate
Phosphoglucoisomerase
Fructose-6-phosphate
ATP
ADP
Phosphofructokinase
Fructose-1, 6-bisphosphate
Aldolase
Isomerase
Dihydroxyacetonephosphate
Glyceraldehyde-3-phosphate
1
2
3
4
5
Aldolase
Isomerase
Fructose-1, 6-bisphosphate
Dihydroxyacetonephosphate
Glyceraldehyde-3-phosphate
4
5
Fig. 9-9-52 NAD+
NADH2
+ 2 H+
2
2 P i
Triose phosphatedehydrogenase
1, 3-Bisphosphoglycerate
6
2 NAD+
Glyceraldehyde-3-phosphate
Triose phosphatedehydrogenase
NADH2
+ 2 H+
2 P i
1, 3-Bisphosphoglycerate
6
2
2
Fig. 9-9-62 NAD+
NADH2
Triose phosphatedehydrogenase
+ 2 H+
2 P i
2
2 ADP
1, 3-Bisphosphoglycerate
Phosphoglycerokinase2 ATP
2 3-Phosphoglycerate
6
7
2
2 ADP
2 ATP
1, 3-Bisphosphoglycerate
3-Phosphoglycerate
Phosphoglycero-kinase
2
7
Fig. 9-9-7
3-Phosphoglycerate
Triose phosphatedehydrogenase
2 NAD+
2 NADH+ 2 H+
2 P i
2
2 ADP
Phosphoglycerokinase
1, 3-Bisphosphoglycerate
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
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
Fig. 9-9-9
Triose phosphatedehydrogenase
2 NAD+
NADH2
2
2
2
2
2
2 ADP
2 ATP
Pyruvate
Pyruvate kinase
Phosphoenolpyruvate
Enolase2 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
Concept 9.3: The citric acid cycle completes the energy-yielding oxidation of organic molecules
• In the presence of O2, pyruvate enters the mitochondrion
• Before the citric acid cycle can begin, 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
Fig. 9-11
Pyruvate
NAD+
NADH
+ H+ Acetyl CoA
CO2
CoA
CoA
CoA
Citricacidcycle
FADH2
FAD
CO22
3
3 NAD+
+ 3 H+
ADP + P iATP
NADH
The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn
also called the Krebs cycle
Fig. 9-12-1
Acetyl CoA
Oxaloacetate
CoA—SH
1
Citrate
Citricacidcycle
Fig. 9-12-2
Acetyl CoA
Oxaloacetate
Citrate
CoA—SH
Citricacidcycle
1
2
H2O
Isocitrate
Fig. 9-12-3
Acetyl CoA
CoA—SH
Oxaloacetate
Citrate
H2O
Citricacidcycle
Isocitrate
1
2
3
NAD+
NADH
+ H+
-Keto-glutarate
CO2
Fig. 9-12-4
Acetyl CoA
CoA—SH
Oxaloacetate
Citrate
H2O
IsocitrateNAD+
NADH
+ H+
Citricacidcycle
-Keto-glutarate
CoA—SH
1
2
3
4
NAD+
NADH
+ H+SuccinylCoA
CO2
CO2
Fig. 9-12-5
Acetyl CoA
CoA—SH
Oxaloacetate
Citrate
H2O
IsocitrateNAD+
NADH
+ H+
CO2
Citricacidcycle
CoA—SH -Keto-
glutarate
CO2NAD+
NADH
+ H+SuccinylCoA
1
2
3
4
5
CoA—SH
GTP GDP
ADP
P iSuccinate
ATP
Fig. 9-12-6
Acetyl CoA
CoA—SH
Oxaloacetate
H2O
CitrateIsocitrate
NAD+
NADH
+ H+
CO2
Citricacidcycle
CoA—SH -Keto-
glutarate
CO2NAD+
NADH
+ H+
CoA—SH
P
SuccinylCoA
i
GTP GDP
ADP
ATP
Succinate
FAD
FADH2
Fumarate
1
2
3
4
5
6
Fig. 9-12-7
Acetyl CoA
CoA—SH
Oxaloacetate
Citrate
H2O
IsocitrateNAD+
NADH
+ H+
CO2
-Keto-glutarate
CoA—SH
NAD+
NADH
SuccinylCoA
CoA—SH
PP
GDPGTP
ADP
ATP
Succinate
FAD
FADH2
Fumarate
CitricacidcycleH2O
Malate
1
2
5
6
7
i
CO2
+ H+
3
4
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
Concept 9.4: During oxidative phosphorylation, chemiosmosis couples electron transport to ATP synthesis
• Following glycolysis and the citric acid cycle, NADH and FADH2 account for most of the energy extracted from food
• These two electron carriers donate electrons to the electron transport chain, which powers ATP synthesis via oxidative phosphorylation
The Pathway of Electron Transport
• is in the cristae of the mitochondrion
• Most of the chain’s components are proteins, which exist in multiprotein complexes
• The carriers alternate reduced and oxidized states as they accept and donate electrons
• Electrons drop in free energy as they go down the chain and are finally 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
Fr e
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–
prothetic groups of cytochromes
flavin nucleotides (tightly bound to flavoproteins) :
determining the sequence of electron carrier by inhibitors:
Chemiosmosis: The Energy-Coupling Mechanism
• Electron transfer in the electron transport chain causes proteins to pump H+ from the mitochondrial matrix to the intermembrane space
• H+ then moves back across the membrane, passing through channels in ATP synthase
• ATP synthase uses the exergonic flow of H+ to drive phosphorylation of ATP
• This is an example of chemiosmosis, the use of energy in a H+ gradient to drive cellular work
Fig. 9-14
INTERMEMBRANE SPACE
Rotor
H+
Stator
Internalrod
Cata-lyticknob
ADP+P ATP
i
MITOCHONDRIAL MATRIX
model for ATP synthesis
• The energy stored in a H+ gradient across a membrane couples the redox reactions of the electron transport chain to ATP synthesis
• The H+ gradient is referred to as a proton-motive force, emphasizing its capacity to do work
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
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
An Accounting of 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 the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 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
What about NADH from glycolysis?
• NADH made in cytosol
• Can’t get into matrix of mitochondrion
• 2 mechanisms
– In muscle and brain
• Glycerol phosphate shuttle
– In liver and heart
• Malate / aspartate shuttle
glycerol-3-phosphate shuttle : (used in skeletal muscle and brain)
In muscle and brain
Each NADH converted to FADH2 inside mitochondrion
FADH2 enters later in the electron transport chain produces 1.5 ATP
Total ATP per glucose in muscle and brain
• Gycerol phosphate shuttle
– 2 NADH per glucose - 2 FADH2
– 2 FADH2 X 1.5 ATP / FADH2……….3.0 ATP
– 2 ATP in glycoysis ……………2.0 ATP
– From pyruvate and Krebs
• 12.5 ATP X 2 per glucose …..25.0 ATP
Total = 30.0 ATP/ glucose
malate-aspartate shuttle : (used in liver, kidney and heart)
Malate – Aspartate Shuttle in cytosol
• In liver and heart
• NADH oxidized while reducing oxaloacetate to malate
– Malated dehydrogenase
• Malate crosses membrane
Malate – Aspartate Shuttle in matrix
• Malate reoxidized to oxaloacetate
– Malate dehydrogenase
– NAD+ reduced to NADH
• NADH via electron transport yields 2.5 ATP
Total ATP per glucose in liver and heart
• Malate – Aspartate Shuttle
– 2 NADH per glucose - 2 NADH
– 2 NADH X 2.5 ATP / NADH…………5.0 ATP
– 2 ATP from glycolysis………………..2.0 ATP
– From pyruvate and Krebs
• 12.5 ATP X 2 per glucose ……..25.0 ATP
• Total = 32.0 ATP/ glucose
Summary
• Total ATP / glucose
– Muscle and brain 30.0 ATP
• Uses glycerol phosphate shuttle
– Heart and liver 32.0 ATP
• Uses malate aspartate shuttle
Concept 9.5: Fermentation and anaerobic respiration enable cells to produce ATP withoutthe use of oxygen
• Most cellular respiration requires O2 to produce ATP
• Glycolysis can produce ATP with or without O2 (in aerobic or anaerobic conditions)
• In the absence of O2, glycolysis couples with fermentation or anaerobic respiration to produce ATP
Fig. 9-18
2 ADP + 2 Pi 2 ATP
Glucose Glycolysis
2 NAD+ 2 NADH
2 Pyruvate
+ 2 H+
2 Acetaldehyde2 Ethanol
(a) Alcohol fermentation
2 ADP + 2 Pi2 ATP
Glucose Glycolysis
2 NAD+ 2 NADH+ 2 H+
2 Pyruvate
2 Lactate
(b) Lactic acid fermentation
2 CO2
Fig. 9-19
Glucose
Glycolysis
PyruvateCYTOSOL
No O2 present:Fermentation
O2 present:
Aerobic cellular respiration
MITOCHONDRION
Acetyl CoAEthanolor
lactate Citricacidcycle
Fermentation and Aerobic Respiration Compared
•Glycolysis probably evolved in ancient prokaryotes before there was oxygen in the atmosphere
•Gycolysis and the citric acid cycle are major intersections to various catabolic and anabolic pathways
The Versatility of Catabolism
• Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration
• Glycolysis accepts a wide range of carbohydrates
• Proteins must be digested to amino acids; amino groups can feed glycolysis or the citric acid cycle
Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings
Fig. 9-20Proteins
Carbohydrates
Aminoacids
Sugars
Fats
Glycerol Fattyacids
Glycolysis
Glucose
Glyceraldehyde-3-
Pyruvate
P
NH3
Acetyl CoA
Citricacidcycle
Oxidativephosphorylation
Biosynthesis (Anabolic Pathways)
beta oxidation
•An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate
•Catabolic pathways funnel electrons
•from many kinds of organic molecules into cellular respiration
Fig. 9-21Glucose
GlycolysisFructose-6-phosphate
Phosphofructokinase
Fructose-1,6-bisphosphateInhibits
AMP
Stimulates
Inhibits
Pyruvate
CitrateAcetyl CoA
Citricacidcycle
Oxidativephosphorylation
ATP
+
––
Regulation of Cellular Respiration via Feedback Mechanisms
1. Feedback inhibition is the most common mechanism for control
2. If ATP concentration begins to drop, respiration speeds up; when there is plenty of ATP, respiration slows down
3. Control of catabolism is based mainly on regulating the activity of enzymes at strategic points in the catabolic pathway
You should now be able to:
1. Name the three stages of cellular respiration; for each, state the region of the eukaryotic cell where it occurs and the products that result
2. In general terms, explain the role of the electron transport chain in cellular respiration
3. Explain where and how the respiratory electron transport chain creates a proton gradient