How Cells make ATP:
Energy-Releasing Pathways
Chapter 8
Learning Objective 1
•
In aerobic respiration, which reactant is
oxidized and which is reduced?
Aerobic Respiration
•
A catabolic process
•
•
Redox reactions
•
•
•
fuel (glucose) broken down to carbon
dioxide and water
transfer electrons from glucose (oxidized)
to oxygen (reduced)
Energy released
•
produces 36 to 38 ATP per glucose
KEY CONCEPTS
•
Aerobic respiration is an exergonic
redox process in which glucose
becomes oxidized, oxygen becomes
reduced, and energy is captured to
make ATP
Learning Objective 2
•
What are the four stages of aerobic
respiration?
4 Stages of
Aerobic Respiration
1.
Glycolysis
2.
Formation of acetyl CoA
3.
Citric acid cycle
4.
Electron transport chain and
chemiosmosis
Glycolysis
•
1 molecule of glucose degraded
•
•
2 ATP molecules (net) produced
•
•
to 2 molecules pyruvate
by substrate-level phosphorylation
4 hydrogen atoms removed
•
to produce 2 NADH
Glycolysis
Glycolysis
Formation
of acetyl
coenzyme A
Citric acid
cycle
Electron transport
and
chemiosmosis
2 ATP
32 ATP
Glucose
Pyruvate
2 ATP
Fig. 8-3, p. 175
GLYCOLYSIS
Energy investment phase and splitting
of glucose
Two ATPs invested per glucose
Glucose
2 ATP
3
steps
2 ADP
Fructose-1,6-bisphosphate
P
P
Glyceraldehyde Glyceraldehyde
phosphate
phosphate
(G3P)
(G3P)
P
P
Fig. 8-3, p. 175
Energy capture phase
Four ATPs and two NADH
produced per glucose
P
P
(G3P)
(G3P)
NAD+
NAD+
NADH
2 ADP
5
steps
NADH
2 ATP
2 ADP
2 ATP
Pyruvate Pyruvate
Net yield per glucose:
Two ATPs and two NADH
Fig. 8-3, p. 175
Formation of Acetyl CoA
•
1 pyruvate molecule
•
•
Acetyl group + coenzyme A
•
•
loses 1 molecule of carbon dioxide
produce acetyl CoA
1 NADH produced per pyruvate
Formation of Acetyl CoA
Glycolysis
Formation
of acetyl
coenzyme A
Citric acid
cycle
Electron transport
and
chemiosmosis
2 ATP
32 ATP
Glucose
Pyruvate
2 ATP
Fig. 8-5, p. 178
Carbon
dioxide
Pyruvate
NAD+
CO2
Coenzyme A
NADH
Acetyl coenzyme A
Fig. 8-5, p. 178
Citric Acid Cycle
•
1 acetyl CoA enters cycle
•
•
•
2 C enter as acetyl CoA
•
•
combines with 4-C oxaloacetate
forms 6-C citrate
2 leave as CO2
1 acetyl CoA
•
•
transfers H atoms to 3 NAD+ , 1 FAD
1 ATP produced
Citric Acid Cycle
Glycolysis
Formation
of acetyl
coenzyme A
Citric acid
cycle
Electron transport
and
chemiosmosis
2 ATP
32 ATP
Glucose
Pyruvate
2 ATP
Fig. 8-6, p. 179
Acetyl coenzyme A
Coenzyme A
Citrate
Oxaloacetate
NADH
NAD+
NAD+
CITRIC
ACID
CYCLE
H2O
NADH
CO2
FADH2
5-carbon compound
FAD
GTP
NADH
GDP
4-carbon compound
ADP
CO2
ATP
Fig. 8-6, p. 179
Electron Transport Chain
•
H atoms (or electrons) transfer
•
•
•
from one electron acceptor to another
in mitochondrial inner membrane
Electrons reduce molecular oxygen
•
forming water
Electron Transport Chain
Cytosol
Outer mitochondrial
membrane
Intermembrane
space
Complex I: NADH–
ubiquinone
Inner
oxidoreductase
mitochondrial
membrane
Matrix of
mitochondrion
Complex II:
Succinate–
ubiquinone
reductase
Complex IV:
Cytochrome c
oxidase
Complex III:
Ubiquinone–
cytochrome c
oxidoreductase
FADH2
FAD
NAD+
2 H+
1/
H2O
2
O2
NADH
Fig. 8-8, p. 181
Oxidative Phosphorylation
•
Redox reactions in ETC are coupled to
ATP synthesis through chemiosmosis
KEY CONCEPTS
•
Aerobic respiration consists of four
stages: glycolysis, formation of acetyl
coenzyme A, the citric acid cycle, and
the electron transport chain and
chemiosmosis
Learning Objective 3
•
Where in a eukaryotic cell does each
stage of aerobic respiration take place?
Aerobic Respiration
•
Glycolysis occurs in the cytosol
•
All other stages in the mitochondria
1
Glycolysis
Glucose
2
Formation of
acetyl
coenzyme A
3
Citric acid
cycle
4
Electron
transport and
chemiosmosis
Mitochondrion
Acetyl
coenzyme
A
Citric
acid
cycle
Electron
transport and
chemiosmosis
2 ATP
32 ATP
Pyruvate
2 ATP
Fig. 8-2, p. 173
Learning Objective 4
•
Add up the energy captured (as ATP,
NADH, and FADH2) in each stage of
aerobic respiration
Energy Capture
•
Glycolysis
•
•
Conversion of 2 pyruvates to acetyl CoA
•
•
2 NADH
Citric acid cycle
•
•
1 glucose: 2 NADH, 2 ATP (net)
2 acetyl CoA: 6 NADH, 2 FADH2, 2 ATP
Total: 4 ATP, 10 NADH, 2 FADH2
Energy Transfer
•
Electron transport chain (ETC)
•
•
10 NADH and 2 FADH2 produce 32 to 34
ATP by chemiosmosis
1 glucose molecule yields 36 to 38 ATP
Energy from Glucose
Substrate-level
Glycolysis
phosphorylation
Glucose
Oxidative
phosphorylation
Pyruvate
Acetyl
coenzyme
A
Citric
acid
cycle
Total ATP from
substrate-level
phosphorylation
Total ATP from
oxidative
phosphorylation
Fig. 8-11, p. 185
Learning Objective 5
•
Define chemiosmosis
•
How is a gradient of protons established
across the inner mitochondrial
membrane?
Chemiosmosis
•
Energy of electrons in ETC
pumps H+ across inner mitochondrial
membrane
• into intermembrane space
•
•
Protons (H+) accumulate in
intermembrane space
•
lowering pH
Proton Gradient
Outer mitochondrial
membrane
Cytosol
Inner mitochondrial
membrane
Intermembrane
space — low pH
Matrix — higher pH
Fig. 8-9, p. 183
Learning Objective 6
•
How does the proton gradient drive ATP
synthesis in chemiosmosis?
ATP Synthase
•
Enzyme ATP synthase
•
•
forms channels through inner mitochondrial
membrane
Diffusion of protons through channels
provides energy to synthesize ATP
ETC and Chemiosmosis
Cytosol
Outer
mitochondrial
membrane
Intermembrane
space
Inner
mitochondrial
membrane
Complex I
Matrix of
mitochondrion
Complex
II
Complex
III
Complex V:
ATP
synthase
Complex
IV
FADH2
NAD+
NADH
1
2
ADP
Pi
ATP
Fig. 8-10a, p. 184
Projections of
ATP synthase
250 nm
(b) This TEM shows hundreds of projections of ATP
synthase complexes along the surface of the inner
mitochondrial membrane.
Fig. 8-10b, p. 184
Learning Objective 7
•
How do the products of protein and lipid
catabolism enter the same metabolic
pathway that oxidizes glucose?
Amino Acids
•
Undergo deamination
•
Carbon skeletons converted
•
to intermediates of aerobic respiration
Lipids
•
Glycerol and fatty acids
•
•
both oxidized as fuel
Fatty acids
•
converted to acetyl CoA by β-oxidation
Catabolic Pathways
PROTEINS CARBOHYDRATES
Amino
acids
FATS
GlycolysisGlycerol Fatty
acids
Glucose
G3P
Pyruvate
CO2
Acetyl
coenzyme
A
Citric
acid
cycle
Electron
transport and
chemiosmosis
End
products: NH3
H2O
CO2
Fig. 8-12, p. 186
PROTEINS CARBOHYDRATES
Amino
acids
Glycolysis
Glucose
FATS
Glycerol Fatty
acids
G3P
Pyruvate
CO2
Acetyl
coenzyme
A
Citric
acid
cycle
Electron
transport and
chemiosmosis
End
products:
Stepped Art
NH3
H2O
CO2
Fig. 8-12, p. 186
KEY CONCEPTS
•
Nutrients other than glucose, including
many carbohydrates, lipids, and amino
acids, can be oxidized by aerobic
respiration
Learning Objective 8
•
Compare the mechanism of ATP
formation, final electron acceptor, and
end products of anaerobic respiration
and fermentation
Anaerobic Respiration
•
Electrons transferred
•
•
•
from fuel molecules to ETC
coupled to ATP synthesis (chemiosmosis)
Final electron acceptor
•
•
inorganic substance
nitrate or sulfate (not molecular oxygen)
KEY CONCEPTS
•
In anaerobic respiration carried out by
some bacteria, ATP is formed during a
redox process in which glucose
becomes oxidized and an inorganic
substance becomes reduced
Fermentation
•
Anaerobic process
•
•
Net energy gain only 2 ATP per glucose
•
•
no ETC
produced by substrate-level
phosphorylation during glycolysis
NAD+
•
produced by transferring H from NADH to
organic compound from nutrient
Fermentation
•
Alcohol fermentation
•
•
•
in yeast cells
waste products: ethyl alcohol, CO2
Lactate (lactic acid) fermentation
•
•
•
some fungi, prokaryotes, animal cells
H atoms added to pyruvate
waste product: lactate
KEY CONCEPTS
•
Fermentation is an inefficient anaerobic
redox process in which glucose
becomes oxidized and an organic
substance becomes reduced
•
Some fungi and bacteria, as well as
muscle cells under conditions of low
oxygen, obtain low yields of ATP
through fermentation
Fermentation
Fig. 8-13, p. 187
25 μm
Fig. 8-13a, p. 187
Glycolysis
Glucose
2 NAD+
2 NADH
2 ATP
2 Pyruvate
CO2
2 Ethyl alcohol
(b) Alcohol fermentation
Fig. 8-13b, p. 187
Glycolysis
Glucose
2 NAD+
2 NADH
2 ATP
2 Pyruvate
2 Lactate
(c) Lactate fermentation
Fig. 8-13c, p. 187
Summary Reaction
•
Complete oxidation of glucose
C6H12O6 + 6 O2 + 6 H2O →
6 CO2 + 12 H2O + energy (36 to 38 ATP)
Summary Reaction
•
Glycolysis
C6H12O6 + 2 ATP + 2 ADP + 2 Pi + 2 NAD+
→ 2 pyruvate + 4 ATP + 2 NADH + H2O
Glycolysis in Detail
Energy investment phase and splitting
of glucose
Two ATPs invested per glucose
Glucose
ATP
Hexokinase
ADP
1 Glycolysis begins with preparation reaction in
which glucose receives phosphate group from
ATP molecule. ATP serves as source of both
phosphate and energy needed to attach phosphate
to glucose molecule. (Once ATP is spent, it
becomes ADP and joins ADP
pool of cell until turned into ATP again.)
Phosphorylated glucose is known as glucose-6phosphate. (Note phosphate attached to its carbon
atom 6.) Phosphorylation of glucose makes it
more chemically reactive.
Glucose-6-phosphate
Phosphoglucoisomerase
Fig. 8-4a, p. 176
2 Glucose-6-phosphate undergoes another
preparation reaction, rearrangement of its
hydrogen and oxygen atoms. In this reaction
glucose-6-phosphate is converted to its isomer,
fructose-6-phosphate.
Fructose-6-phosphate
ATP
Phosphofructokinase
ADP
Fructose-1,6-bisphosphate
3 Next, another ATP donates phosphate to
molecule, forming fructose-1,6-bisphosphate.
So far, two ATP molecules have been invested
in process without any being produced.
Phosphate groups are now bound at carbons
1 and 6, and molecule is ready to be split.
Aldolase
Isomerase
Dihydroxyacetone
phosphate
4 Fructose-1,6-bisphosphate is then
split into two 3-carbon sugars,
glyceraldehyde-3- phosphate (G3P)
and dihydroxyacetone phosphate.
5 Dihydroxyacetone phosphate is
enzymatically converted to its
isomer, glyceraldehyde-3Glyceraldehydephosphate, for further metabolism
3-phosphate (G3P)
in glycolysis.
Fig. 8-4a, p. 176
Two glyceraldehyde-3-phosphate (G3P)
from bottom of previous page
2 NAD+
Energy capture phase
Four ATPs and two NADH produced per
glucose
Glyceraldehyde-3-phosphate dehydrogenase
2 NADH
6 Each glyceraldehyde-3-phosphate undergoes dehydrogenation
with NAD+ as hydrogen acceptor. Product
of this very exergonic reaction is phosphoglycerate,
which reacts with inorganic phosphate present in
cytosol to yield 1,3-bisphosphoglycerate.
Two 1,3-bisphosphoglycerate
2 ADP
Phosphoglycerokinase
2 ATP
7 One of phosphates of 1,3-bisphosphoglycerate reacts
with ADP to form ATP. This transfer of phosphate from
phosphorylated intermediate to ATP is referred to as
substrate-level phosphorylation.
Two 3-phosphoglycerate
Phosphoglyceromutase
Fig. 8-4b, p. 177
8 3-phosphoglycerate is rearranged to 2-phosphoglycerate
by enzymatic shift of position of phosphate group.
This is a preparation reaction.
Two 2-phosphoglycerate
2 H2O
Enolase
9 Next, molecule of water is removed, which results in
formation of double bond. The product,
phosphoenolpyruvate (PEP), has phosphate group
attached by an unstable bond (wavy line).
Two
phosphoenolpyruvate
2 ADP
Pyruvate kinase
2 ATP
10 Each of two PEP molecules transfers its phosphate group
to ADP to yield ATP and pyruvate. This is substrate-level
phosphorylation reaction.
Two pyruvate
Fig. 8-4b, p. 177
Summary Reaction
•
Conversion of pyruvate to acetyl CoA
2 pyruvate + 2 coenzyme A + 2 NAD+ →
2 acetyl CoA + 2 CO2 + 2 NADH
Summary Reaction
•
Citric acid cycle
2 acetyl CoA + 6 NAD+ + 2 FAD + 2 ADP
+ 2 Pi + 2 H2O → 4 CO2 + 6 NADH +
2 FADH2 + 2 ATP + 2 CoA
Citric Acid Cycle in Detail
Summary Reactions
•
Hydrogen atoms in ETC
NADH + 3 ADP + 3 Pi + 12 O2 → NAD+ +
3 ATP + H2O
FADH2 + 2 ADP + 2 Pi + 12 O2 → FAD +
2 ATP + H2O
Summary Reaction
•
Lactate fermentation
C6H12O6 → 2 lactate + energy (2 ATP)
Summary Reaction
•
Alcohol fermentation
C6H12O6 → 2 CO2 + 2 ethyl alcohol +
energy (2 ATP)
The Overall Reactions of
Glycolysis
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