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Cellular Respiration: Harvesting Chemical Energy
Chapter 9
 Assemble
polymers, pump substances across
membranes, move and reproduce
 The

giant panda
Obtains energy for its cells by eating plants which get
their energy from the sun (sun in, heat out)
Figure 9.1
 Energy

Flows into an ecosystem as sunlight and leaves as heat
Light energy
ECOSYSTEM
Photosynthesis
in chloroplasts
Organic
CO2 + H2O
+ O2
Cellular
molecules
respiration
in mitochondria
ATP
powers most cellular work
Figure 9.2
Heat
energy
 Catabolic
pathways yield energy by oxidizing
organic fuels
 The

breakdown of organic molecules is exergonic
Release of energy by the transfer of e-
 Organic
molecules possess PE due to atom
arrangements
 Compounds participating in exergonic
reactions act as fuels
 Enzymes help degrade molecules to release
PE
 One

catabolic process, fermentation
Is a partial degradation of sugars that occurs without
oxygen
 Cellular



respiration
Is the most prevalent and efficient catabolic pathway
Consumes oxygen and organic molecules such as glucose
Yields ATP


Aerobic
Anaerobic (bacteria)
 To
keep working

Cells must regenerate ATP

C6H12O6 +6O2
6CO2 + 6H2O + Energy (ATP +heat)
 Catabolic

pathways yield energy
Due to the transfer of electrons
 Redox

reactions
Transfer electrons from one reactant to another by
oxidation and reduction
 In

A substance loses electrons, or is oxidized
 In

oxidation
reduction
A substance gains electrons, or is reduced
 Examples
of redox reactions
becomes oxidized
(loses electron)
Na
+
Cl
Na+
+
becomes reduced
(gains electron)
Cl–
 Some
Products
Reactants
becomes oxidized
+
CH4
CO
2O2
+
Energy
2 H2O
becomes reduced
O
O
O
C
O
H
H
C
+
2
O
H
H
H

Do not completely exchange electrons
Change the degree of electron sharing in covalent bonds
H

redox reactions
Methane
(reducing
agent)
Figure 9.3
Oxygen
(oxidizing
agent)
Carbon dioxide
Water
Oxidation of Organic Fuel Molecules During
Cellular Respiration
• During cellular respiration
– Glucose is oxidized and oxygen is reduced
becomes oxidized
C6H12O6 + 6O2
6CO2 + 6H2O + Energy
becomes reduced
Reducing Agent is the electron donor (sugar)
Oxidizing Agent is the electron acceptor (oxygen)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Breaking down of Sugar (Redox Reactions)
• Key Players
– Dehydrogenase (enzyme strips H atoms)
– NAD+ (coenzyme used to shuttle e-)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Players
• Dehydrogenase removes a pair of H atoms (2
e-, 2 p) from glucose thus oxidizing it.
• Dehydrogenase delivers 2e- and 1 p to NAD+
and the other proton is releases as H+ ion.
NAD+ is now NADH (stores energy for later
use)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
How do you get energy from NADH?
• ETC
– e- carry molecules in inner membrane of
mitochondria
– e- move down from one carrier to another
through REDOX reactions
– At the bottom, oxygen captures the e- with
hydrogen to form water
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Stepwise Energy Harvest via NAD+ and the Electron
Transport Chain
• Cellular respiration
– Oxidizes glucose in a series of steps
– Steps slow the reaction and allow the
controlled release of energy that can be used
instead of a massive loss
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
 Electrons

from organic compounds
Are usually first transferred to NAD+, a coenzyme
2 e– + 2 H+
NAD+
Dehydrogenase
O
NH2
H
C
CH2
O
O
N+ Nicotinamide
(oxidized form)
Reduction of NAD+
+ 2[H]
(from food) Oxidation of NADH
O–
O P
O
H
–
O P O HO
O
H
OH
HO
CH2
NH2
N
N
H
O
H
HO
N
H
OH
N
2 e– + H+
H
Figure 9.4
NADH
H O
C
H
N
NH2
Nicotinamide
(reduced form)
+
 NADH,

the reduced form of NAD+
Passes the electrons to the electron transport chain


electron transfer is not stepwise
A large release of energy occurs
As in the reaction of hydrogen and oxygen to form water
H2 + 1/2 O2
Free energy, G
 If
Figure 9.5 A
Explosive
release of
heat and light
energy
H2O
(a) Uncontrolled reaction
 The


electron transport chain
Passes electrons in a series of steps instead of in one
explosive reaction
Uses the energy from the electron transfer to form ATP
2H
1/
+
2
O2
1/
O2
(from food via NADH)
Free energy, G
2 H+ + 2 e–
Controlled
release of
energy for
synthesis of
ATP
ATP
ATP
ATP
2 e–
2 H+
H2O
Figure 9.5 B
(b) Cellular respiration
2
 Respiration
is a cumulative function of three
metabolic stages



Glycolysis
The citric acid cycle
Oxidative phosphorylation
 Glycolysis


Occurs in the cytosol
Breaks down glucose into two molecules of pyruvate
 The


citric acid cycle (Krebs)
Occurs in the mitochondria
Completes the breakdown of glucose


Releases CO2
Makes e- available for MASS production of ATP
 Oxidative



phosphorylation
Occurs in the mitochondra
Is driven by the electron transport chain
Generates ATP
 An
overview of cellular respiration
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Glycolsis
Pyruvate
Glucose
Cytosol
ATP
Figure 9.6
Substrate-level
phosphorylation
Citric
acid
cycle
Oxidative
phosphorylation:
electron
transport and
chemiosmosis
Mitochondrion
ATP
Substrate-level
phosphorylation
ATP
Oxidative
phosphorylation
 Both

glycolysis and the citric acid cycle
Can generate ATP by substrate-level phosphorylation
Enzyme
Enzyme
ADP
P
Substrate
+
Figure 9.7
Product
ATP
 Glycolysis
pyruvate
 Glycolysis



harvests energy by oxidizing glucose to
Means “splitting of sugar”
Breaks down glucose into pyruvate
Occurs in the cytoplasm of the cell
 Glycolysis


consists of two major phases
Energy investment phase
Energy payoff phase
Citric
acid
cycle
Glycolysis
Oxidative
phosphorylation
ATP
ATP
ATP
Energy investment phase
Glucose
2 ATP + 2 P
2 ATP
used
Energy payoff phase
4 ADP + 4 P
2 NAD+ + 4 e- + 4 H
+
4 ATP formed
2 NADH + 2 H+
2 Pyruvate + 2 H2O
Glucose
4 ATP formed – 2 ATP used
Figure 9.8
2 NAD+ + 4 e– + 4 H
+
2 Pyruvate + 2 H2O
2 ATP + 2 H+
2 NADH
A
closer look at the energy investment phase
CH2OH
H
HH
HO H
HO
OH
H OH
Glycolysis
Glucose
ATP
1
Hexokinase
ADP
CH2OH P
HH OH
OH H
HO
H OH
Glucose-6-phosphate
2
Phosphoglucoisomerase
CH2O P
O CH2OH
H HO
HO
H
HO H
Fructose-6-phosphate
ATP
3
Phosphofructokinase
ADP
P O CH2 O CH2 O P
HO
H
OH
HO H
Fructose1, 6-bisphosphate
4
Aldolase
5
H
P O CH2 Isomerase
C O
C O
CHOH
CH2OH
CH2 O P
Figure 9.9 A
Dihydroxyacetone
phosphate
Glyceraldehyde3-phosphate
Citric
Oxidative
acid
cycle phosphorylation
A
closer look at the energy payoff phase
6
Triose phosphate
dehydrogenase
2 NAD+
2 Pi
2 NADH
+ 2 H+
2
P
O C O
CHOH
CH2 O P
1, 3-Bisphosphoglycerate
2 ADP
7
Phosphoglycerokinase
2 ATP
O–
2
C
CHOH
CH2 O P
3-Phosphoglycerate
8
Phosphoglyceromutase
2
O–
C
O
H C O
P
CH2OH
2-Phosphoglycerate
9
Enolase
2H O
2
2
O–
C O
C O
P
CH2
Phosphoenolpyruvate
2 ADP
10
Pyruvate kinase
2 ATP
2
O–
C O
C O
Figure 9.8 B
CH3
Pyruvate
2
ATP
 2NADH
 The
citric acid cycle completes the energy-yielding
oxidation of organic molecules
 The citric acid cycle


Takes place in the matrix of the mitochondrion
Active transport takes pyruvate into the mitochondria
 Before

the citric acid cycle can begin
Pyruvate must first be converted to acetyl CoA, which links
the cycle to glycolysis
CYTOSOL
MITOCHONDRION
NAD+
NADH
+ H+
O–
S
CoA
C
O
2
C
C
O
O
1
3
CH3
Pyruvate
Transport protein
Figure 9.10
CH3
Acetyle CoA
CO2
Coenzyme A
C
atom of carboxyl
group removed
and released as
CO2
 Remaining 2 C
compound is
oxidized to form
acetate and
NAD+=NADH
 Coenzyme
A
attaches to
acetate=acetyl coA
which has a high
PE
MITOCHONDRI
ON
CYTOSOL
NAD
H
NAD+
O–
+
H+
S
Co
A
C
O
2
C
C
O
O
1
3
CH3
Pyruvate
Transport protein
Figure 9.10
CO2
Coenzyme
A
CH3
Acetyle
CoA
 Generation
of
Acetyl coA makes:

1 NADH for each
pyruvate
2
NADH have now
been made
 An
overview of the citric acid cycle
Pyruvate
(from glycolysis,
2 molecules per glucose)
Glycolysis
Citric
acid
cycle
ATP
ATP
Oxidative
phosphorylatio
n
ATP
CO2
CoA
NADH
+ 3 H+ Acetyle CoA
CoA
CoA
Citric
acid
cycle
2 CO2
3 NAD+
FADH2
3 NADH
FAD
+ 3 H+
ADP + P i
ATP
Figure 9.11
A
closer look at the citric acid cycle
Glycolysis
Citric
Oxidative
acid phosphorylation
cycle
S
CoA
C
O
CH3
Acetyl CoA
CoA SH
O
NADH
+ H+
C COO–
COO–
1
CH2
8 Oxaloacetate
HO C
COO–
COO–
CH2
COO–
HO CH
H2O
CH2
COO–
NAD+
CH2
2
HC COO–
COO–
Malate
Figure
CH2
HO
Citrate
9.12
Isocitrate
COO–
H2O
CO2
Citric
acid
cycle
7
CH
COO–
3
NAD+
COO–
COO–
CH
Fumarate
HC
CH2
CoA SH
6
CoA SH
COO–
FAD
CH2
CH2
C O
COO–
Succinate
Pi
S
CoA
GTP GDP Succinyl
CoA
ADP
ATP
Figure 9.12
C O
COO–
CH2
5
CH2
FADH2
4
COO–
NAD+
NADH
+ H+
+ H+
α-Ketoglutarate
CH2
COO–
NADH
CO2
 One
cycle produces 3 NADH, 1 FADH2 and 1
ATP
 GO AROUND TWICE!!!!

So that is a total of:

6 NADH, 2 FADH2 and 2 ATP
 Made


of two parts:
ETC
Chemiosmosis
 Collection
of molecules embedded in inner membrane
of mitocondria
 In the electron transport chain

Electrons from NADH and FADH2 lose energy in several steps
 At

Electrons are passed to oxygen, forming water
NO ATP is made but e- energy becomes manageable
NADH
50
FADH2
Free energy (G) relative to O2 (kcl/mol)

the end of the chain
40
I
Fe•S
30
20
Multiprotein
complexes
FAD
Fe•S II
O
III
Cyt b
Fe•S
Cyt c1
IV
Cyt c
Cyt a
Cyt a3
10
0
Figure 9.13
FMN
2 H + + 1⁄2 O2
H2 O
 Energy
coupling
mechanism
 Energy is stored in
H+ gradient across
a membrane
 It is used to drive
the production of
ATP
 ATPase
is needed
 ATP

synthase
Is the enzyme that actually makes ATP
INTERMEMBRANE SPACE
H+
H+
H+
H+
H+
H+
H+
A rotor within the
membrane spins
clockwise when
H+ flows past
it down the H+
gradient.
A stator anchored
in the membrane
holds the knob
stationary.
H+
ADP
+
Pi
Figure 9.14
MITOCHONDRIAL MATRIX
ATP
A rod (for “stalk”)
extending into
the knob also
spins, activating
catalytic sites in
the knob.
Three catalytic
sites in the
stationary knob
join inorganic
Phosphate to ADP
to make ATP.
 At

certain steps along the electron transport chain
Electron transfer causes protein complexes to pump H+
from the mitochondrial matrix to the intermembrane space
 The



resulting H+ gradient
Stores energy
Drives chemiosmosis in ATP synthase
Is referred to as a proton-motive force
 Chemiosmosis
Inner
Mitochondrial
membrane
Oxidative
phosphorylation.
electron transport
and chemiosmosis
Glycolysis
ATP
and the electron transport chain
ATP
ATP
H+
H+
H+
Intermembrane
space
Protein complex
of electron
carners
Q
I
Inner
mitochondrial
membrane
Figure 9.15
IV
III
ATP
synthase
II
FADH2
NADH+
Mitochondrial
matrix
H+
Cyt c
NAD+
FAD+
2 H+ + 1/2 O2
H2O
ADP +
(Carrying electrons
from, food)
ATP
Pi
H+
Chemiosmosis
Electron transport chain
+
ATP
synthesis
powered by the flow
Electron transport and pumping of protons (H ),
+
+
which create an H gradient across the membrane Of H back across the membrane
Oxidative phosphorylation
 Net
production of 36-38 ATP
An Accounting of ATP Production by Cellular
Respiration
• During respiration, most energy flows in this
sequence
– Glucose to NADH to electron transport chain to
proton-motive force to ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
 There
are three main processes in this metabolic
enterprise
Electron shuttles
span membrane
CYTOSOL
MITOCHONDRION
2 NADH
or
2 FADH2
2 NADH
2 NADH
Glycolysis
Glucose
2
Pyruvate
2
Acetyl
CoA
+ 2 ATP
by substrate-level
phosphorylation
Maximum per glucose:
Figure 9.16
6 NADH
Citric
acid
cycle
+ 2 ATP
2 FADH2
Oxidative
phosphorylation:
electron transport
and
chemiosmosis
+ about 32 or 34 ATP
by substrate-level by oxidative phosphorylation, depending
on which shuttle transports electrons
phosphorylation
from NADH in cytosol
About
36 or 38 ATP
 Fermentation
enables some cells to produce ATP
without the use of oxygen
 Cellular respiration

Relies on oxygen to produce ATP
 In

the absence of oxygen
Cells can still produce a small amount of ATP through
fermentation
 Glycolysis



Can produce ATP with or without oxygen, in aerobic or
anaerobic conditions
It is the ETC that requires oxygen (without it the e- are not
pulled down the series of proteins and chemiosmosis fails)
Glycolysis can couple with fermentation to produce ATP
 Fermentation

consists of:
Glycolysis plus reactions that regenerate NAD+, which can
be reused by glyocolysis
 During



lactic acid fermentation
Pyruvate is reduced directly to NADH to form lactate as a
waste product
NAD+ is now free to accept e- and make 2 ATP from
remaining sugar molecule (s)
Lactate accumulates in muscles=sore and fatigued
 In

alcohol fermentation
Pyruvate is converted to ethanol in two steps, one of which
releases CO2
2 ADP + 2
P1
2 ATP
O–
C O
Glucose
Glycolysis
C O
CH3
2 Pyruvate
2 NADH
2 NAD+
H
2 CO2
H
C O
H C OH
CH3
CH3
2 Ethanol
2 Acetaldehyde
(a) Alcohol fermentation
2 ADP + 2
Glucose
P1
2 ATP
Glycolysis
O–
C O
C O
O
2 NAD+
C O
H
C OH
CH3
2 Lactate
Figure 9.17
(b) Lactic acid fermentation
2 NADH
CH3
 Both

fermentation and cellular respiration
Use glycolysis to oxidize glucose and other organic fuels to
pyruvate
 Fermentation

Differ in their final electron acceptor
 Cellular

and cellular respiration
respiration
Produces more ATP
 Pyruvate
is a key juncture in catabolism
Glucose
CYTOSOL
Pyruvate
No O2 present
Fermentation
O2 present
Cellular respiration
MITOCHONDRION
Ethanol
or
lactate
Figure 9.18
Acetyl CoA
Citric
acid
cycle
 Catabolic

pathways
Funnel electrons from many kinds of organic molecules
into cellular respiration
 The
catabolism of various molecules from food
 Food
isn’t just for energy
 Biosynthesis-making of cellular molecules for repair
and growth

Consumption of ATP