Chapter 07
Lecture and
Animation Outline
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7.1 Learning Objectives
• Review energy transformations important for life
• Define autotrophs & heterotrophs
• Understand role of redox reactions & electron
carriers in energy metabolism.
• Define respiration vs. fermentation
• Discuss the 2 ways ATP is made
2
Energy Transformations
H 2O
CO2
cell respiration
photosynthesis
C6H12O6
O2
3
Energy in Our Food
http://theitaliankitchenelp.com/ItalianKitchenMobile/FoodImages/HamburgerAndFries.jpg
4
How Organisms Obtain Energy
• Autotrophs
– Produce their own
organic molecules
through
photosynthesis
• Heterotrophs
http://upload.wikimedia.org/wikipedia/com
mons/3/3f/Ferns02.jpg
– Eat organic
compounds produced
by other organisms
5
http://upload.wikimedia.org/wikipedia/commons/1/19/Tanzanian_Animals.jpg
Cellular (Aerobic) respiration
C6H12O6 + 6O2
6CO2 + 6H2O
ΔG = – 686 kcal/mol of glucose
• This large amount of energy must be
released in small steps rather than all at
once, but how…
6
Cellular Respiration
• Cellular respiration is a series of redox
reactions
• Oxidation – loss of electrons (LEO)
• Reduction – gain of electron (GER)
• Dehydrogenation – lost electrons are
accompanied by protons
– A hydrogen atom is lost (1 electron, 1 proton)
– To follow the e-, follow the H’s!!!!!!!!
7
Redox- The Electron Carriers
• During redox reactions, electrons carry
energy from one molecule to another
• Electron Carriers in Cell Respiration are…
• Nicotinamide adenosine dinucleotide
(NAD+)
– Reduced form = NADH (2 e-, 2 H+)
• Flavin adenine dinucleotide (FAD)
– Reduced form = FADH2 (2 e-, 2H+)
8
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
H
O
H
Reduction
C
H
NH2 + 2H
O
NH2 + H+
C
Oxidation
N
O
O
P
CH2
N
O
O
O–
O
O
OH
O
O–
O
NH2
OH
OH
N
O
N
O
H
OH
H
P
O
O–
OH
NAD+: Oxidized form of nicotinamide
N
H
N
CH2
O
Adenine
H
NH2
OH
N
N
H
CH2
H
H
N
P
P
O
O–
H
H
O
CH2
N
H
Adenine
H
H
OH
OH
NADH: Reduced form of nicotinamide
9
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Oxidation
Energy-rich
molecule
Enzyme
H
Product
Reduction
H
+H+
H
H
H
H
2e–
H+
H
NAD+
NAD+
NAD
H
NAD
NAD+
1. Enzymes that use NAD+
as a coenzyme for oxidation
reactions bind NAD+ and the
substrate.
2. In an oxidation–reduction
reaction, 2 electrons and
a proton are transferred
to NAD+, forming NADH.
A second proton is
donated to the solution.
3. NADH diffuses away
and can then donate
electrons to other
molecules.
10
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Electrons from food
2e–
Energy released
for ATP synthesis
High energy
Low energy
2H+
1/ O
2 2
H2O
11
Respiration vs. Fermentation
• Aerobic respiration
– Final electron receptor is oxygen (O2)
• Anaerobic respiration
– Final electron acceptor is an inorganic
molecule (not O2)
• Fermentation
– Final electron acceptor is an organic
molecule, converted into lactic acid or ethanol
+ CO2
12
ATP
• Cells use ATP to drive endergonic
reactions
– ΔG (free energy) = –7.3 kcal/mol
• 2 mechanisms for synthesis
1. Substrate-level phosphorylation
• Transfer phosphate group directly to ADP
• During glycolysis & Krebs (Citric Acid) Cycle
2. Oxidative phosphorylation
• ATP synthase uses energy from a proton gradient
• During ETC and Chemiosmosis
13
Substrate-level Phosphorylation
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PEP
P
Enzyme
Enzyme
P
P
– ADP
– ATP
Adenosine
14
Question 1
Which of the following processes uses an inorganic
molecule besides oxygen as a terminal electron
acceptor?
a. Aerobic respiration
b. Fermentation
c. Anaerobic respiration
d. All of the above
7.2 Learning Objectives
• Describe the process of glycolysis.
– Where does it take place in the cell
– What goes in, what comes out
– Why is ATP required to start glycolysis
– Is O2 required for glycolysis
• Calculate the energy yield from glycolysis.
16
Oxidation of Glucose
The complete oxidation of glucose proceeds
in stages:
1. Glycolysis
2. Pyruvate oxidation
3. Krebs cycle
4. Electron transport chain & chemiosmosis
17
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Outer
mitochondrial
membrane
Glycolysis
Glucose
Intermembrane
space
Pyruvate
Oxidation
Krebs
Cycle
Inner
mitochondrial
membrane
Electron
Transport Chain
Chemiosmosis
18
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Outer
mitochondrial
membrane
Glycolysis
Glucose
NADH
ATP
Intermembrane
space
Pyruvate
Pyruvate
Oxidation
NADH
Acetyl-CoA
Mitochondrial
matrix
CO2
CO2
NADH
Krebs
Cycle
FADH2
e–
NAD+ FAD O2
ATP
H2O
e–
Electron e–
Transport Chain
Inner
mitochondrial
membrane
ATP
Chemiosmosis
ATP Synthase
H+
19
Glycolysis
• Converts 1 glucose (6 carbons) to 2 pyruvate
(3 carbons)
• 10-step biochemical pathway
• Occurs in the cytoplasm
• Net production of 2 ATP molecules by
substrate-level phosphorylation
• 2 NADH produced by the reduction of NAD+
– Only process that occurs in red blood cells since
they do not have mitochondria!
20
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Glycolysis
NADH
Pyruvate Oxidation
Krebs
Cycle
Electron Transport Chain
Chemiosmosis
ATP
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Glycolysis
ATP
NADH
Fig. 7.6-2
Pyruvate Oxidation
Krebs
Cycle
Electron Transport Chain
Chemiosmosis
Priming Reactions
6-carbon glucose
(Starting material)
ATP
ATP
ADP
P
ADP
P
6-carbon sugar diphosphate
Glycolysis begins
with the addition of
energy. Two highenergy phosphates
(P) from two
molecules of ATP
are added to the
6-carbon molecule
glucose, producing
a 6-carbon
molecule with two
phosphates.
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Glycolysis
ATP
NADH
Fig. 7.6-3
Pyruvate Oxidation
Krebs
Cycle
Electron Transport Chain
Chemiosmosis
Priming Reactions
6-carbon glucose
(Starting material)
ATP
ATP
ADP
P
ADP
P
Cleavage
6-carbon sugar diphosphate
P
3-carbon sugar
phosphate
Glycolysis begins
with the addition of
energy. Two highenergy phosphates
(P) from two
molecules of ATP
are added to the
6-carbon molecule
glucose, producing
a 6-carbon
molecule with two
phosphates.
P
3-carbon sugar
phosphate
Then, the 6-carbon
molecule with two
phosphates is split in
two, forming two
3-carbon sugar
phosphates.
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Glycolysis
ATP
NADH
Fig. 7.6
Pyruvate Oxidation
Krebs
Cycle
Electron Transport Chain
Chemiosmosis
Glycolysis begins
with the addition of
energy. Two highenergy phosphates
(P) from two
molecules of ATP
are added to the
6-carbon molecule
glucose, producing
a 6-carbon
molecule with two
phosphates.
Priming Reactions
6-carbon glucose
(Starting material)
ATP
ATP
ADP
P
ADP
P
6-carbon sugar diphosphate
Cleavage
Then, the 6-carbon
molecule with two
phosphates is split in
two, forming two
3-carbon sugar
phosphates.
P
3-carbon sugar
phosphate
P
3-carbon sugar
phosphate
Oxidation and ATP Formation
Pi
Pi
NAD+
NAD+
NADH
NADH
ADP
ADP
ATP
ATP
ADP
ADP
ATP
ATP
3-carbon
pyruvate
3-carbon
pyruvate
An additional
Inorganic phosphate (
Pi ) is incorporated into
each 3-carbon sugar
phosphate. An
oxidation reaction
converts the two
sugar phosphates
into intermediates
that can transfer a
phosphate to ADP to
form ATP. The
oxidation reactions
also yield NADH
giving a net energy
yield of 2 ATP and 2
NADH.
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NADH
Glucose
Pyruvate Oxidation
Fig. 7.7-1
ATP
Electron Transport Chain
Chemiosmosis
O
1
Hexokinase
Krebs
Cycle
CH2OH
Glycolysis: The Reactions
Glucose
ATP
ADP
Glucose 6-phosphate
Glucose
6-phosphate
Glycolysis
CH2
O
O
P
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NADH
Glucose
Pyruvate Oxidation
Fig. 7.7-2
ATP
Electron Transport Chain
Chemiosmosis
1. Phosphorylation of
glucose by ATP.
O
1
Hexokinase
Krebs
Cycle
CH2OH
Glycolysis: The Reactions
Glucose
ATP
ADP
Glucose 6-phosphate
Glucose
6-phosphate
Glycolysis
CH2
O
O
P
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Glucose
NADH
Glucose
Fig. 7.7-3
1
ATP
Hexokinase
Krebs
Cycle
ADP
Glucose 6-phosphate
2
Electron Transport Chain
Chemiosmosis
Phosphoglucose
isomerase
Fructose 6-phosphate
3
ATP
Phosphofructokinase
1. Phosphorylation of
glucose by ATP.
ADP
Fructose 1,6-bisphosphate
2–3. Rearrangement,
followed by a second
ATP phosphorylation.
O
Aldolase
4
5
Isomerase
Dihydroxyacetone
phosphate
Glyceraldehyde 3phosphate (G3P)
Glucose
6-phosphate
Pyruvate Oxidation
CH2OH
Glycolysis: The Reactions
CH2
CH2
O
O
P
P
O
O
Fructose
6-phosphate
ATP
Fructose
1,6-bisphosphate
Glycolysis
O
CH2
P
CH2OH
CH2
O
O
P
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Glucose
NADH
Glucose
Fig. 7.7-4
Glucose 6-phosphate
2
Electron Transport Chain
Chemiosmosis
Phosphoglucose
isomerase
Fructose 6-phosphate
3
ATP
Phosphofructokinase
1. Phosphorylation of
glucose by ATP.
ADP
Fructose 1,6-bisphosphate
2–3. Rearrangement,
followed by a second
ATP phosphorylation.
4–5. The 6-carbon molecule
is split into two 3-carbon
molecules—one G3P,
another that is converted
into G3P in another
reaction.
Aldolase
4
5
Isomerase
Dihydroxyacetone
phosphate
Glyceraldehyde 3phosphate (G3P)
CH2
P
P
O
O
CH2
O
O
O
P
CH2
P
CH2OH
CH2
O
P
O
P
O
O
CH2
C
O
CH2OH
Glyceraldehyde
3-phosphate
Hexokinase
ADP
Glucose
6-phosphate
1
ATP
Krebs
Cycle
O
Fructose
6-phosphate
Pyruvate Oxidation
CH2OH
Glycolysis: The Reactions
Fructose
1,6-bisphosphate
ATP
Dihydroxyacetone
Phosphate
Glycolysis
H
C
O
CHOH
CH2
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CH2OH
Glucose
Glycolysis: The Reactions
NADH
Glucose
Fig. 7.7-5
Glucose
6-phosphate
1
Hexokinase
Krebs
Cycle
ADP
Glucose 6-phosphate
2
Electron Transport Chain
Chemiosmosis
Phosphoglucose
isomerase
Fructose 6-phosphate
3
ATP
Phosphofructokinase
1. Phosphorylation of
glucose by ATP.
ADP
Fructose 1,6-bisphosphate
2–3. Rearrangement,
followed by a second
ATP phosphorylation.
4–5. The 6-carbon molecule
is split into two 3-carbon
molecules—one G3P,
another that is converted
into G3P in another
reaction.
6. Oxidation followed by
phosphorylation produces
two NADH molecules and
two molecules of BPG,
each with one
high-energy phosphate
bond.
4
Aldolase
5
Isomerase
Dihydroxyacetone
phosphate
Glyceraldehyde 3phosphate (G3P)
6
NAD+
NADH
Pi
Pi
NAD+
NADH
Glyceraldehyde
3-phosphate
dehydrogenase
1,3-Bisphosphoglycerate
1,3-Bisphosphoglycerate
(BPG)
(BPG)
CH2
P
P
O
O
Fructose
6-phosphate
ATP
Fructose
1,6-bisphosphate
Pyruvate Oxidation
O
CH2
P
O
O
O
P
CH2OH
CH2
CH2
O
P
O
P
O
CH2
O
C
O
CH2OH
P
O
Glyceraldehyde
3-phosphate
ATP
1,3-Bisphospho- Dihydroxyacetone
glycerate
Phosphate
Glycolysis
C
H
C
O
CHOH
CH2
O
CHOH
CH2
O
P
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CH2OH
Glucose
Glycolysis: The Reactions
NADH
Glucose
Fig. 7.7-6
Glucose
6-phosphate
1
Krebs
Cycle
Glucose 6-phosphate
2
Electron Transport Chain
Chemiosmosis
Phosphoglucose
isomerase
Fructose 6-phosphate
3
ATP
Phosphofructokinase
1. Phosphorylation of
glucose by ATP.
ADP
Fructose 1,6-bisphosphate
2–3. Rearrangement,
followed by a second
ATP phosphorylation.
4–5. The 6-carbon molecule
is split into two 3-carbon
molecules—one G3P,
another that is converted
into G3P in another
reaction.
6. Oxidation followed by
phosphorylation produces
two NADH molecules and
two molecules of BPG,
each with one
high-energy phosphate
bond.
7. Removal of high-energy
phosphate by two ADP
molecules produces two
ATP molecules and leaves
two 3PG molecules.
4
Aldolase
5
Isomerase
Dihydroxyacetone
phosphate
Glyceraldehyde 3phosphate (G3P)
6
NAD+
Pi
Pi
NAD+
NADH
NADH
Glyceraldehyde
3-phosphate
dehydrogenase
1,3-Bisphosphoglycerate
1,3-Bisphosphoglycerate
(BPG)
(BPG)
7
ADP
ATP
3-Phosphoglycerate
(3PG)
P
ADP
Phosphoglycerate
kinase
ATP
3-Phosphoglycerate
(3PG)
CH2
P
O
O
Fructose
6-phosphate
Hexokinase
ADP
Fructose
1,6-bisphosphate
ATP
1,3-Bisphospho- Dihydroxyacetone
glycerate
Phosphate
Pyruvate Oxidation
O
CH2
P
O
O
O
P
CH2OH
CH2
CH2
O
P
O
P
O
Glyceraldehyde
3-phosphate
ATP
CH2
O
C
O
CH2OH
P
O
C
H
C
O
CHOH
CH2
O
CHOH
CH2
O
O–
3-Phosphoglycerate
Glycolysis
C
O
CHOH
CH2
O
P
P
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CH2OH
Glucose
Glycolysis: The Reactions
NADH
Glucose
Fig. 7.7-7
Glucose
6-phosphate
1
2
Electron Transport Chain
Chemiosmosis
Phosphoglucose
isomerase
Fructose 6-phosphate
3
ATP
Phosphofructokinase
1. Phosphorylation of
glucose by ATP.
ADP
Fructose 1,6-bisphosphate
2–3. Rearrangement,
followed by a second
ATP phosphorylation.
4–5. The 6-carbon molecule
is split into two 3-carbon
molecules—one G3P,
another that is converted
into G3P in another
reaction.
6. Oxidation followed by
phosphorylation produces
two NADH molecules and
two molecules of BPG,
each with one
high-energy phosphate
bond.
7. Removal of high-energy
phosphate by two ADP
molecules produces two
ATP molecules and leaves
two 3PG molecules.
4
Aldolase
5
Isomerase
Dihydroxyacetone
phosphate
Glyceraldehyde 3phosphate (G3P)
6
NAD+
Pi
Pi
NAD+
NADH
NADH
Glyceraldehyde
3-phosphate
dehydrogenase
1,3-Bisphosphoglycerate
1,3-Bisphosphoglycerate
(BPG)
(BPG)
7
ADP
ATP
8–9. Removal of water yields
two PEP molecules, each
with a high-energy
phosphate bond.
P
ATP
3-Phosphoglycerate
(3PG)
CH2
2-Phosphoglycerate
(2PG)
2-Phosphoglycerate
(2PG)
9
H2O
Enolase
Phosphoenolpyruvate
(PEP)
H2O
Phosphoenolpyruvate
(PEP)
P
O
O
O
P
CH2OH
CH2
CH2
O
P
O
P
O
CH2
O
C
O
CH2OH
O
P
C
H
C
O
CHOH
CH2
O
CHOH
CH2
O
O–
C
O
CHOH
P
O
CH2
8
Phosphoglyceromutase
P
O
O
ADP
Phosphoglycerate
kinase
3-Phosphoglycerate
(3PG)
CH2
Fructose
6-phosphate
Glucose 6-phosphate
Fructose
1,6-bisphosphate
Krebs
Cycle
1,3-Bisphospho- Dihydroxyacetone
glycerate
Phosphate
Hexokinase
ADP
3-Phosphoglycerate
ATP
2-Phosphoglycerate
Pyruvate Oxidation
O
Glyceraldehyde
3-phosphate
ATP
O–
H
C
O
C
O
P
CH2OH
Phosphoenolpyruvate
Glycolysis
O–
C
O
C
O
CH2
P
P
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CH2OH
Glycolysis: The Reactions
NADH
Glucose
Fig. 7.7
Glucose
6-phosphate
1
Phosphoglucose
isomerase
Fructose 6-phosphate
3
ATP
Phosphofructokinase
1. Phosphorylation of
glucose by ATP.
ADP
Fructose 1,6-bisphosphate
2–3. Rearrangement,
followed by a second
ATP phosphorylation.
6. Oxidation followed by
phosphorylation produces
two NADH molecules and
two molecules of BPG,
each with one
high-energy phosphate
bond.
7. Removal of high-energy
phosphate by two ADP
molecules produces two
ATP molecules and leaves
two 3PG molecules.
Dihydroxyacetone
phosphate
Glyceraldehyde 3phosphate (G3P)
6
NAD+
Pi
NAD+
Pi
NADH
NADH
Glyceraldehyde
3-phosphate
dehydrogenase
1,3-Bisphosphoglycerate
1,3-Bisphosphoglycerate
(BPG)
(BPG)
7
ADP
ATP
P
ATP
3-Phosphoglycerate
(3PG)
CH2
2-Phosphoglycerate
(2PG)
2-Phosphoglycerate
(2PG)
9
H2O
H2O
Enolase
Phosphoenolpyruvate
(PEP)
Phosphoenolpyruvate
(PEP)
ADP
10
ADP
ATP
Pyruvate kinase
ATP
Pyruvate
Pyruvate
P
O
O
O
P
CH2OH
CH2
CH2
O
P
O
P
O
CH2
O
C
O
CH2OH
O
P
C
H
C
O
CHOH
CH2
O
CHOH
CH2
O
O–
C
O
CHOH
P
O
CH2
8
Phosphoglyceromutase
P
O
O
ADP
Phosphoglycerate
kinase
3-Phosphoglycerate
(3PG)
8–9. Removal of water yields
two PEP molecules, each
with a high-energy
phosphate bond.
10. Removal of high-energy
phosphate by two ADP
molecules produces two
ATP molecules and two
pyruvate molecules.
5
Isomerase
2-Phosphoglycerate
4–5. The 6-carbon molecule
is split into two 3-carbon
molecules—one G3P,
another that is converted
into G3P in another
reaction.
4
Aldolase
CH2
Fructose
6-phosphate
2
Electron Transport Chain
Chemiosmosis
Fructose
1,6-bisphosphate
Glucose 6-phosphate
O–
H
C
O
C
O
P
CH2OH
Phosphoenolpyruvate
Krebs
Cycle
1,3-Bisphospho- Dihydroxyacetone
glycerate
Phosphate
Hexokinase
ADP
3-Phosphoglycerate
ATP
O–
C
O
C
O
P
CH2
O–
Pyruvate
Pyruvate Oxidation
O
Glyceraldehyde
3-phosphate
ATP
Glucose
Glycolysis
C
O
C
O
CH3
P
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33
NADH must be recycled
• For glycolysis to continue, NADH must be
recycled to NAD+ by either:
1. Aerobic respiration
– Oxygen is available as the final electron
acceptor
– Produces significant amount of ATP
2. Fermentation
– Occurs when oxygen is not available
– Organic molecule is the final electron
acceptor
34
Fate of pyruvate
• Depends on oxygen availability.
– When oxygen is present, pyruvate is oxidized
to acetyl-CoA which enters the Krebs cycle
• Aerobic respiration
– Without oxygen, pyruvate is reduced in order
to oxidize NADH back to NAD+
• Fermentation
35
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Without oxygen
Pyruvate
With oxygen
H2O
O2
NAD+
CO2
NADH
NADH
Acetaldehyde
ETC in mitochondria
Acetyl-CoA
NAD+
NADH
Lactate
NAD+
Krebs
Cycle
Ethanol
36
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Outer
mitochondrial
membrane
Glycolysis
Glucose
NADH
ATP
Pyruvate
Intermembrane
space
Question 4
Glycolysis costs ____ ATPs, but makes ___ ATPs; thus
it has a net yield of ___ ATPs.
a. 3, 6, 3
b. 2, 4, 2
c. 2, 2, 0
d. 0, 2, 2
e. 4, 8, 4
Question 6
All of the glycolysis reactions do not require oxygen and
can take place in an anaerobic environment.
a. This is true
b. This is false
7.3-7.4 Learning Objectives
• For both pyruvate oxidation and the Krebs
cycle
– Where does it take place in the cell
– What goes in, what comes out
– What is energy yield
40
Pyruvate Oxidation
• In the presence of oxygen, pyruvate is
oxidized
– Occurs in the mitochondria in eukaryotes
– Occurs at the plasma membrane in
prokaryotes
41
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Outer
mitochondrial
membrane
Glycolysis
Glucose
NADH
ATP
Intermembrane
space
Pyruvate
Pyruvate
Oxidation
Acetyl-CoA
Mitochondrial
matrix
Products of pyruvate oxidation
• For each 3-carbon pyruvate molecule:
– 1 CO2
• Decarboxylation by pyruvate dehydrogenase
– 1 NADH
– 1 acetyl-CoA which consists of 2 carbons from
pyruvate attached to coenzyme A
• Acetyl-CoA proceeds to the Krebs cycle
43
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Glycolysis
Pyruvate Oxidation
NADH
Krebs
Cycle
Electron Transport Chain
Chemiosmosis
Pyruvate Oxidation: The Reaction
Pyruvate
Pyruvate
O–
C
O
C
O
CH 3
CO2
NADH
CoA
Acetyl Coenzyme A
Acetyl Coenzyme A
NAD+
S
CoA
C
O
CH3
44
Question 12
An experimental drug blocks the decarboxylation
reactions that convert pyruvate into acetyl-CoA. A cell
treated with this drug would not be able to complete
glycolysis.
a. This is true
b. This is false
Krebs Cycle
• Oxidizes the acetyl group from pyruvate
• Occurs in the matrix of the mitochondria
• Biochemical pathway of 9 steps in three
segments
1. Acetyl-CoA + oxaloacetate → citrate
2. Citrate rearrangement and decarboxylation
3. Regeneration of oxaloacetate
46
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Glycolysis
Pyruvate Oxidation
NADH
FADH2
Krebs
Cycle
CoA(Acetyl-CoA)
4-carbon
molecule
(oxaloacetate)
ATP
Electron Transport Chain
Chemiosmosis
CoA
6-carbon molecule
(citrate)
NADH
NAD +
NADH
NAD+
CO2
Pyruvate from glycolysis is
oxidized Krebs Cycle into an
acetyl group that feeds into the
Krebs cycle. The 2-C acetyl group
combines with 4-C oxaloacetate to
produce the 6-C compound citrate
(thus this is also called the citric
acid cycle). Oxidation reactions
are combined with two
decarboxylations to produce
NADH, CO2, and a new 4-carbon
molecule. Two additional
oxidations generate another
NADH and an FADH2 and
regenerate the original 4-C
oxaloacetate.
4-carbon
molecule
Krebs Cycle
5-carbon
molecule
NAD+
FADH2
NADH
FAD
CO2
4-carbon
molecule
4-carbon
molecule
ATP
ADP +
P
47
Products of the Krebs Cycle
• For each Acetyl-CoA entering:
– Release 2 molecules of CO2
– Reduce 3 NAD+ to 3 NADH
– Reduce 1 FAD (electron carrier) to FADH2
– Produce 1 ATP
– Regenerate oxaloacetate
48
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Glycolysis
1. Reaction 1: Condensation
2–3. Reactions 2 and 3: Isomerization
Pyruvate Oxidation
4. Reaction 4: The first oxidation
5. Reaction 5: The second oxidation
NADH
Krebs
Cycle
FADH2
ATP
6. Reaction 6: Substrate-level phosphorylation
7. Reaction 7: The third oxidation
Electron T ransport Chain
Chemiosmosis
8–9. Reactions 8 and 9: Regeneration of
oxaloacetate and the fourth oxidation
Krebs Cycle: The Reactions
Acetyl-CoA
HO— CH
O═C
CH2
9
COO—
═
CH3— C— S
Citrate (6C)
COO—
CoA-SH
— — — —
— — —
Malate (4C)
COO—
— — —
NADH
NAD+
CoA
—
O
Oxaloacetate (4C)
COO—
1
CH2
Citrate
synthetase
HO— C — COO—
Malate
dehydrogenase
CH2
CH2
COO—
COO—
2
H2O
Aconitase
3
8 Fumarase
Isocitrate (6C)
Fumarate (4C)
COO—
— — — —
— ═ —
COO—
CH
CH2
HC — COO—
HC
COO—
HO — CH
COO—
FADH2
FAD
7
Succinate
dehydrogenase
Isocitrate
dehydrogenase 4
Succinate (4C)
NAD+
CO2
COO—
— — —
NADH
CH2
-Ketoglutarate (5C)
CoA-SH
Succinyl-CoA
synthetase
GTP
ADP
6
GDP + Pi
CO2
COO—
CH2
CH2
C═ O
ATP
COO—
Succinyl-CoA (4C)
S — CoA
CH2
-Ketoglutarate
dehydrogenase
5
CoA-SH
— — — —
COO—
— — — —
CH2
CH2
C —O
NAD+
NADH
COO—
49
At this point…
• Glucose has been oxidized to:
– 6 CO2
– 4 ATP
– 10 NADH
– 2 FADH2
These electron carriers proceed
to the electron transport chain
• Electron transfer has released 53 kcal/mol
of energy by gradual energy extraction
• Energy will be put to use to manufacture
ATP
50
Question 5
The 2 carbons in acetyl–CoA are eventually used to form
—
a. Glucose
b. ATP
c. Pyruvate
d. Oxaloacetate
e. Carbon dioxide
7.5-7.6 Learning Objectives
• Describe the structure and function of the
electron transport chain.
• Diagram how the proton gradient connects
electron transport with ATP synthesis.
• Calculate the number of ATP molecules
produced by aerobic respiration.
52
Electron Transport Chain (ETC)
• ETC is a series of membrane-bound
electron carriers
• Embedded in the inner mitochondrial
membrane (cristae)
• Electrons from NADH and FADH2 are
transferred to complexes of the ETC
• Each complex
– A proton pump creating proton gradient
– Transfers electrons to next carrier
53
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http://farm3.static.flickr.com/2229/2278663151_d6720d77fb.jpg
54
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Glycolysis
Pyruvate Oxidation
Krebs
Cycle
ATP
Electron Transport Chain
Chemiosmosis
H++
H
ATP
Mitochondrial matrix
NADH dehydrogenase
NADH + H+
Cytochrome
oxidase complex
bc1 complex
2H+ + 1/2O2
NAD+
ATP
synthase
ADP + Pi
H2O
FADH2
2 e– FAD
22 e–
22 e–
Q
Inner
mitochondrial
membrane
C
H+
H+
H+
H+
Intermembrane space
a. The electron transport chain
b. Chemiosmosis
55
Chemiosmosis
• Accumulation of protons in the
intermembrane space drives protons into
the matrix via diffusion
• Membrane relatively impermeable to ions
• Most protons can only reenter matrix
through ATP synthase
– Uses energy of gradient to make ATP from
ADP + Pi
56
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H+
Mitochondrial
matrix
ATP
ADP + Pi
Catalytic head
Stalk
Rotor
Intermembrane
space
H+
H+
H+
H+
H+
H+
57
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Glycolysis
NADH
Glucose
Pyruvate
Pyruvate
Oxidation
NADH
CO2
Acetyl-CoA
NADH
CO2
Krebs
Cycle
e–
H+
32 ATP
FADH2
2 ATP
e–
H2O
2H+
+
1/ O
2 2
e–
Q
C
H+
H+
H+
58
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59
Energy Yield of Respiration
• Theoretical energy yield (these values
vary from book to book)
– 38 ATP per glucose for bacteria
– 36 ATP per glucose for eukaryotes
• Actual energy yield
– 30 ATP per glucose for eukaryotes
– Reduced yield is due to
• “Leaky” inner membrane
• Use of the proton gradient for purposes other than
ATP synthesis
60
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Glucose
2 ATP
2
ATP
5
ATP
Glycolysis
Pyruvate
2
NADH
Chemiosmosis
Pyruvate oxidation
Krebs
Cycle
2
6
NADH
NADH
5
ATP
2
ATP
15
ATP
Chemiosmosis
2
FADH2
3
ATP
Total net ATP yield = 32
(30 in eukaryotes)
61
Question 7
What is the function of the coenzymes, NADH and
FADH2 ?
a. Charging electrons to power ATP synthase
b. Catalyzing the formation of acetyl-CoA
c. Providing electrons and H+ to the electron
transport chain
d. Transporting CO2 into the mitochondria
e. Acting as a terminal electron acceptor
Question 16
What happens to the electron’s energy as it moves
through the electron transport chain?
a. The electrons gain energy through each
transfer
b. The electrons lose energy through each
transfer
c. The energy content is unchanged
d. The energy drops to a different orbital
7.8-7.9 Learning Objectives
• Compare anaerobic and aerobic
respiration.
– What are used as final e- acceptors
• Distinguish between fermentation and
anaerobic respiration.
• Understand how proteins and fats are
used in energy metabolism.
64
Oxidation Without O2
1. Anaerobic respiration
– Use of inorganic molecules (other than O2) as
final electron acceptor
– Many prokaryotes use sulfur, nitrate, carbon
dioxide or even inorganic metals
2. Fermentation
– Use of organic molecules as final electron
acceptor
65
Anaerobic respiration
• Methanogens
– CO2 is reduced to CH4 (methane)
– Found in diverse organisms including cows
• Sulfur bacteria
– Inorganic sulphate (SO4) is reduced to
hydrogen sulfide (H2S)
– Early sulfate reducers set the stage for
evolution of photosynthesis
66
Sulfur-Respiring Prokaryotes
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a.
0.625 µm
b.
a: © Wolfgang Baumeister/Photo Researchers, Inc.; b: NPS Photo
67
Fermentation
• Reduces organic molecules in order to
regenerate NAD+
1. Ethanol fermentation occurs in yeast
– CO2, ethanol, and NAD+ are produced
2. Lactic acid fermentation
– Occurs in animal cells (especially muscles,
such as during sprinting)
– Electrons are transferred from NADH to
pyruvate to produce lactic acid
68
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Alcohol Fermentation in Yeast
H
Glucose
2 ADP
2 ATP
O–
C
O
C
O
G
L
Y
C
O
L
Y
S
I
S
H
OH
CH3
2 NAD+
2 Ethanol
2 NADH
H
C
CO2
2 Pyruvate
CH3
C
O
CH3
2 Acetaldehyde
Lactic Acid Fermentation in Muscle Cells
O–
Glucose
2 ADP
2 ATP
O–
C
O
C
O
CH3
G
L
Y
C
O
L
Y
S
I
S
H
2 NAD+
C
O
C
OH
CH3
2 Lactate
2 NADH
69
2 Pyruvate
Question 13
When making wine, grape juice and yeast are sealed
into a container. Why must the container be air tight?
a. To prevent the buildup of lactic acid
b. Fermentation only occurs in the absence of
oxygen
c. Yeast cannot live in aerobic environments
d. To prevent the yeast from dying
e. To increase the production of acetyl-CoA
Catabolism of Protein
• Amino acids undergo deamination to
remove the amino group
• Remainder of the amino acid is converted
to a molecule that enters glycolysis or the
Krebs cycle
– Alanine is converted to pyruvate
– Aspartate is converted to oxaloacetate
71
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HO
O
HO
Urea
C
H2N
H
H
C
C
C
C
H
H
O
C
O
H
C
H
H
C
H
NH3
H
C
HO
C
O
HO
Glutamate
O
α-Ketoglutarate
72
Catabolism of Fat
• Fats are broken down to fatty acids and
glycerol
– Fatty acids are converted to acetyl groups by
b-oxidation
– Oxygen-dependent process
• The respiration of a 6-carbon fatty acid
yields 20% more energy than 6-carbon
glucose.
73
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— —
H
— —
H
H
H
Fatty acid — C — C — C
O
OH
ATP
CoA
AMP + PPi
H
H
O
═
— —
H
— —
H
Fatty acid — C — C — C — CoA
FAD
Fatty acid
2C shorter
FADH2
O
═
H
—
—
H
H
O
Fatty acid — C ═ C — C — CoA
H2O
— —
H
H
═
— —
HO
Fatty acid — C — C — C — CoA
NAD+
CoA
NADH
H
O
═
═
—
O
Fatty acid — C — C — C — CoA
—
H
Acetyl-CoA
Krebs
Cycle
74
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Macromolecule
degradation
Nucleic acids
Proteins
Polysaccharides
Lipids and fats
Cell building blocks
Nucleotides
Amino acids
Sugars
Fatty acids
Glycolysis
b-oxidation
Deamination
Oxidative respiration
Pyruvate
Acetyl-CoA
Krebs
Cycle
Ultimate metabolic products
NH3
H2O
CO2
75
Question 8
The process of removing the amino group from an amino
acid is —
a. Decarboxylation
b. Defenestration
c. Denaturation
d. Deamination
e. Deracciation
Question 9
Beta-oxidation is used to extract energy from —
a. Glucose
b. Proteins
c. Nucleic acids
d. Carbohydrates
e. Triglycerides
Question 14
A cheeseburger contains bread, meat and cheese.
Which portion of this meal produces the most ATP
per unit of mass?
a. Bread
b. Meat
c. Cheese
d. All are equal
Final Review
79
Question 2
NADH is made during –
a.
b.
c.
d.
Glycolysis
Pyruvate oxidation
Krebs cycle
All of the above
Question 3
Most of the ATP made by aerobic respiration is made
during –
a. Glycolysis
b. Electron transport chain
c. Pyruvate oxidation
d. Krebs cycle
e. Substrate-level phosphorylation