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Ch 9 Cellular Respiration
Extracting usable energy from organic molecules
• Energy flows into ecosystems as sunlight
• Photosynthesis generates organic molecules
and O2 .
• Cellular respiration breaks down organic
molecules to generate ATP;uses O2.
------>fuels cellular activities
LE 9-2
Light
energy
ECOSYSTEM
Photosynthesis
in chloroplasts
Organic + O
molecules 2
CO2 + H2O
Cellular respiration
in mitochondria
ATP
powers most cellular work
Heat
energy
If eukaryotes have mitochondria are they capable of
of aerobic respiration?
Does this include protists, fungi, plants and animals?
You bet!
Cellular Respiration
Net Reaction:
C6H12O6 + 6O2
6CO2 + 6H2O + ATP
glucose
Energy
molecule
Redox reaction
C6H12O6 oxidized to CO2
O2 reduced to H2O
Is cellular respiration endergonic or exergonic?
Anabolic or catabolic?
Exergonic (exothermic)
Catabolic (breaks down molecules
to release energy)
LE 9-6_1
Cytosol
Intermembrane space
Cristae
Glycolysis
Matrix
Pyruvate
Glucose
Mitochondrion
Cytosol
Inner membrane
Outer membrane
ATP
Substrate-level
phosphorylation
Mitochondrion
Three major steps in cellular respiration
1. Glycolysis: the breaking of sugar
In cytosol
2. Citric acid cycle (Krebs Cycle)
In mitochondria
3. Oxidative phosphorylation
LE 9-6_1
Glycolysis
Pyruvate
Glucose
Cytosol
Mitochondrion
ATP
Substrate-level
phosphorylation
Glycolysis
6C organic molecule-->--> 2(3C) organic molecule
1 glucose
-->
2 pyruvates
Is the conversion of glucose to pyruvate a simple
one step process?
NO
Requires 10 enzyme catalyzed reactions!
LE 9-9a_1
Glucose
ATP
Hexokinase
ADP
Glucose-6-phosphate
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidation
phosphorylation
ATP
LE 9-9a_2
Glucose
ATP
Hexokinase
ADP
Glucose-6-phosphate
Phosphoglucoisomerase
Fructose-6-phosphate
ATP
Phosphofructokinase
ADP
Fructose1, 6-bisphosphate
Aldolase
Isomerase
Dihydroxyacetone
phosphate
Glyceraldehyde3-phosphate
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidation
phosphorylation
ATP
LE 9-9b_1
2 NAD+
Triose phosphate
dehydrogenase
2 NADH
+ 2 H+
1, 3-Bisphosphoglycerate
2 ADP
Phosphoglycerokinase
2 ATP
3-Phosphoglycerate
Phosphoglyceromutase
2-Phosphoglycerate
LE 9-9b_2
2 NAD+
Triose phosphate
dehydrogenase
2 NADH
+ 2 H+
1, 3-Bisphosphoglycerate
2 ADP
Phosphoglycerokinase
2 ATP
3-Phosphoglycerate
Phosphoglyceromutase
2-Phosphoglycerate
2 H2O
Enolase
Phosphoenolpyruvate
2 ADP
Pyruvate kinase
2 ATP
Pyruvate
LE 9-8
Energy investment phase
Glucose
2 ATP used
2 ADP + 2 P
Glycolysis
Citric
acid
cycle
Oxidative
phosphorylation
Energy payoff phase
ATP
ATP
ATP
4 ADP + 4 P
2 NAD+ + 4 e– + 4 H+
4 ATP formed
2 NADH + 2 H+
2 Pyruvate + 2 H2O
Net
Glucose
4 ATP formed – 2 ATP used
2 NAD+ + 4 e– + 4 H+
2 Pyruvate + 2 H2O
2 ATP
2 NADH + 2 H+
What is NAD+?
NAD+ + e- + H- --> NADH
An electron carrier
LE 9-6_2
2. Citric acid cycle
(aka Krebs cycle)
Glycolysis
Glucose
Pyruvate
Citric
acid
cycle
Cytosol
ATP
Substrate-level
phosphorylation
ATP
Substrate-level
phosphorylation
Mitochondrion
Reactions in the Mitochondrion
Conversion of pyruvate (3C) to acetyl coA (2C)
In what compartment?
Matrix
LE 9-10
MITOCHONDRION
CYTOSOL
NAD+
NADH
+ H+
Acetyl Co A
Pyruvate
Transport protein
CO2
Coenzyme A
LE 9-11
Pyruvate
(from glycolysis,
2 molecules per glucose)
CO2
NAD+
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidation
phosphorylation
CoA
Where is this
pathway
taking place?
NADH
+ H+
Acetyl CoA
ATP
CoA
Citric
acid
cycle
e- carrier
FADH2
2 CO2
3 NAD+
3 NADH
+ 3 H+
FAD
ADP + P i
ATP
e- carrier
Third step
Oxidative phosphorylation
1. Electron transport chain
2. Chemiosmosis
In what compartment?
Inner mitochondrial membrane
LE 9-13
NADH
50
Free energy (G) relative to O2 (kcal/mol)
FADH2
40
FMN
I
Multiprotein
complexes
FAD
Fe•S II
Fe•S
Q
III
Cyt b
30
Fe•S
Cyt c1
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidative
phosphorylation:
electron transport
and chemiosmosis
IV
Cyt c
Cyt a
ATP
Cyt a3
20
10
Oxygen final e- acceptor,
most electronegative
0
2 H+ O2
+ 1/2
H2O
LE 9-15
Oxidative phosphorylation
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidative
phosphorylation:
electron transport
and chemiosmosis
ATP
H+
H+
H+
H+
Intermembrane
space
Cyt c
Protein complex
of electron
carriers
Q
IV
III
I
ATP
synthase
II
Inner
mitochondrial
membrane
FADH2
NADH
+ H+
2H+ + 1/2 O2
NAD+
(carrying electrons
from food)
Mitochondrial
matrix
H2O
FAD
ATP
ADP + P i
H+
Electron transport chain
Pumping of protons (H+),
creates H+ gradient across the membrane
Chemiosmosis
ATP synthesis powered
by diffusion of H+ into matrix
LE 9-14
INTERMEMBRANE SPACE
H+
H+
H+
H+
H+
H+
A rotor within the
membrane spins
as shown when
H+ flows past
it down the H+
gradient.
H+
A stator anchored
in the membrane
holds the knob
stationary.
A rod (or “stalk”)
extending into
the knob also
spins, activating
catalytic sites in
the knob.
H+
ADP
+
P
ATP
i
MITOCHONDRAL MATRIX
Three catalytic
sites in the
stationary knob
join inorganic
phosphate to
ADP to make
ATP.
LE 9-16
Electron shuttles
span membrane
CYTOSOL
2 NADH
Glycolysis
Glucose
2
Pyruvate
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
2
Acetyl
CoA
+ 2 ATP
6 NADH
Citric
acid
cycle
+ 2 ATP
by substrate-level
phosphorylation
by substrate-level
phosphorylation
Maximum per glucose:
About
36 or 38 ATP
2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 32 or 34 ATP
by oxidation phosphorylation, depending
on which shuttle transports electrons
from NADH in cytosol
3 ATP/NADH
2 ATP/ FADH2
Fermentation
production of ATP anaerobically (without O2)
How?
Glycolysis only (fermentation)
• Two fermentation pathways
– alcohol fermentation
– lactic acid fermentation
LE 9-18
Glucose
CYTOSOL
Pyruvate
No O2 present
Fermentation
O2 present
Cellular respiration
MITOCHONDRION
Ethanol
or
lactate
Acetyl CoA
Citric
acid
cycle
LE 9-17a
2 ADP + 2 P i
Glucose
2 ATP
Glycolysis
2 Pyruvate
2 NAD+
2 Ethanol
Alcohol fermentation
2 NADH
+ 2 H+
2 CO2
2 Acetaldehyde
LE 9-17b
2 ADP + 2 P i
Glucose
2 ATP
Glycolysis
2 NAD+
2 NADH
+ 2 H+
2 CO2
2 Pyruvate
2 Lactate
Lactic acid fermentation
Under what circumstances does anaerobic respiration
or fermentation occur?
In O2-starved muscles
accumulation of lactic acid
painful: toxic
In some micro-organisms: bacteria, yeast
exploited for production of alcoholic beverages
cheeses
Evolutionary Significance of Glycolysis
• Glycolysis occurs in nearly all organisms
• May have evolved in ancient prokaryotes before
oxygen in atmosphere
Regulation of ATP synthesis
Negative and positive feedback loops
LE 9-20
Glucose
AMP
Glycolysis
Fructose-6-phosphate
–
Stimulates
+
Phosphofructokinase
–
Fructose-1,6-bisphosphate
Inhibits
Inhibits
Pyruvate
ATP
Citrate
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation
The Versatility of Catabolism
• Catabolic pathways
– funnel electrons from many organic molecules into cellular
respiration
• Glycolysis
– accepts wide range of carbohydrates
• Proteins
– digested to amino acids; amino groups feed glycolysis or the
citric acid cycle
• Fats
– digested to glycerol (used in glycolysis) and fatty acids (used
in generating acetyl CoA)
LE 9-19
Proteins
Carbohydrates
Amino
acids
Sugars
Glycerol Fatty
acids
Glycolysis
Glucose
Glyceraldehyde-3- P
NH3
Fats
Pyruvate
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation