Download Chapter 9

Chapter 8
• Overview: The Energy of Life
• The living cell
– Is a miniature factory where thousands of
reactions occur
– Converts energy in many ways
Figure
8.1
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin
Cummings
• Metabolism
– Is the totality of an organism’s chemical
reactions
– Arises from interactions between molecules
Metabolism= Catabolism + Anabolism
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• At maximum stability
– The system is at equilibrium
Not Stable
• More free energy (higher G)
• Less stable
• Greater work capacity
In a spontaneously change
• The free energy of the system
decreases (∆G<0)
• The system becomes more stable
• The released free energy can
be harnessed to do work
Yeah!
.
More STABLE
• Less free energy (lower G)
• More stable
• Less work capacity
(a) Gravitational motion. Objects
move spontaneously from a
higher altitude to a lower one.
Figure 8.5
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
(b) Diffusion. Molecules
in a drop of dye diffuse
until they are randomly
dispersed.
(c) Chemical reaction. In a
cell, a sugar molecule is
broken down into simpler
molecules.
• An analogy for cellular respiration
Not stable
∆G < 0
∆G < 0
∆G < 0
Stable
Figure 8.7
(c) A multistep open hydroelectric system. Cellular respiration is
analogous to this system: Glucose is broken down in a series
of exergonic reactions that power the work of the cell. The product
of each reaction becomes the reactant for the next, so no reaction
reaches equilibrium.
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Structure and Hydrolysis of ATP
• ATP (adenosine triphosphate)
– Is the cell’s energy shuttle
– Provides energy for cellular functions
Adenine
N
O
O
-O
O
-
O
-
O
O
C
C
N
HC
O
O
O
NH2
-
Phosphate groups
Figure 8.8
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
N
CH2
O
H
N
H
H
H
OH
CH
C
OH
Ribose
• Energy is released from ATP
– When the terminal phosphate bond is broken
P
P
P
Adenosine triphosphate (ATP)
H2O
P
i
+
Figure 8.9 Inorganic phosphate
P
P
Adenosine diphosphate (ADP)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Energy
• ATP hydrolysis
–
Can be coupled to other reactions
Endergonic reaction: ∆G is positive, reaction
is not spontaneous
NH2
Glu
+
Glutamic
acid
NH3
Glu
Ammonia
Glutamine
∆G = +3.4 kcal/mol
Exergonic reaction: ∆ G is negative, reaction
is spontaneous
ATP
Figure 8.10
+
H2O
ADP +
Coupled reactions: Overall ∆G is negative;
together, reactions are spontaneous
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
P
∆G = + 7.3 kcal/mol
∆G = –3.9 kcal/mol
• The three types of cellular work
– Are powered by the hydrolysis of ATP
P
i
P
Motor protein
Protein moved
(a) Mechanical work: ATP phosphorylates motor proteins
Membrane
protein
ADP
+
ATP
P
P
Solute
P
i
Solute transported
(b) Transport work: ATP phosphorylates transport proteins
P
Glu + NH3
Reactants: Glutamic acid
and ammonia
Figure 8.11
NH2
Glu
+
P
i
Product (glutamine)
made
(c) Chemical work: ATP phosphorylates key reactants
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
i
Organization of the Chemistry of Life into
Metabolic Pathways
• A metabolic pathway has many steps
– That begin with a specific molecule and end
with a product
– That are each catalyzed by a specific enzyme
Enzyme 1
A
Enzyme 2
D
C
B
Reaction 1
Enzyme 3
Reaction 2
Starting
molecule
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Reaction 3
Product
• Catabolic pathways
– Break down complex molecules into simpler
compounds
– Exergonic reaction - Release energy
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Anabolic pathways
– Build complicated molecules from simpler ones
– Consume energy
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Forms of Energy
• Energy
– Is the capacity to cause change
– Exists in various forms, of which some can
perform work
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Kinetic energy
– Is the energy associated with motion
• Potential energy
– Is stored in the location of matter
– Includes chemical energy stored in molecular
structure
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Chapter 9
Cellular Respiration: Harvesting Chemical Energy
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Overview: Life Is Work
• Living cells
– Require transfusions of energy from outside
sources to perform their many tasks
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The giant panda
– Obtains energy for its cells by eating plants
Figure 9.1
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Energy
– Flows into an ecosystem as sunlight and
leaves as heatLight energy
ECOSYSTEM
Photosynthesis
in chloroplasts
Organic
CO2 + H2O
+ O2
Cellular
molecules
respiration
in mitochondria
ATP
powers most cellular work
Figure 9.2
Heat
energy
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 9.1: Catabolic pathways yield energy
by oxidizing organic fuels
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Catabolic Pathways and Production of ATP
• The breakdown of organic molecules is
exergonic- releases energy
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• One catabolic process, fermentation
– Is a partial degradation of sugars that occurs
without oxygen
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Cellular respiration
– Is the most prevalent and efficient catabolic
pathway
– Consumes oxygen and organic molecules
such as glucose
– Yields ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Redox Reactions: Oxidation and Reduction
• Catabolic pathways yield energy
– Due to the transfer of electrons from high
potential energy (i.e. in animal cell from
Glucose)
to
– Low potential energy (electron acceptor
usually an electron carrier, but ultimately
delivered to oxygen in the mitochondria)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Principle of Redox
• Redox reactions
– Transfer electrons from one reactant to
another by oxidation and reduction
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• In oxidation
– A substance loses electrons, or is oxidized
• In reduction
– A substance gains electrons, or is reduced
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Examples of redox reactions
becomes oxidized
(loses electron)
Na
+
Cl
Na+
+
becomes reduced
(gains electron)
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Cl–
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
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Electrons from organic compounds
– Are usually first transferred to NAD+, a
coenzyme- electron carrier
2 e– + 2 H+
NAD+
Dehydrogenase
O
NH2
H
C
CH2
O
O–
O
O P
O
H
–
O P O HO
O
N+ Nicotinamide
(oxidized form)
H
OH
HO
CH2
N
H
O
H
HO
N
H
OH
Reduction of NAD+
+ 2[H]
(from food) Oxidation of NADH
NH2
N
N
2 e– + H+
H
Figure 9.4
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
NADH
H O
C
H
N
NH2
Nicotinamide
(reduced form)
+
• NADH, the reduced form of NAD+
– Passes the electrons to the electron transport
chain or system (ETC also known as the ETS)
in the Mitochondria
Intermembrane space
MATRIX
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• If electron transfer is not stepwise
– A large release of energy occurs
– As in the reaction of hydrogen and oxygen to
form water
Free energy, G
H2 + 1/2 O2
Figure 9.5 A
Explosive
release of
heat and light
energy
H2O
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
(a) Uncontrolled reaction
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
(b) Cellular respiration
2
The Stages of Cellular Respiration: A Preview
• Respiration is a cumulative function of three
metabolic stages
– Glycolysis
– The citric acid cycle
– Oxidative phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Glycolysis
– Breaks down glucose into two molecules of
pyruvate
• The citric acid cycle
– Completes the breakdown of glucose
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Oxidative phosphorylation
– Is driven by the electron transport chain that
occurs in the Mitochondria
– Generates ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• A animal cell
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Mitochondria are enclosed by two membranes
– A smooth outer membrane
– An inner membrane folded into cristae
Mitochondrion
Intermembrane space
Outer
membrane
Free
ribosomes
in the
mitochondrial
matrix
Inner
membrane
Cristae
Matrix
Figure 6.17
Mitochondrial
DNA
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
100 µm
• An overview of cellular respiration
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
Citric
acid
cycle
Glycolsis
Pyruvate
Glucose
Cytosol
Mitochondrion
ATP
Figure 9.6
Oxidative
phosphorylation:
electron
transport and
chemiosmosis
Substrate-level
phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Product
ATP
• Concept 9.2: Glycolysis harvests energy by
oxidizing glucose to pyruvate
• Glycolysis
– Means “splitting of sugar”
– Breaks down glucose into pyruvate
– Occurs in the cytoplasm of the cell
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2 NAD+ + 4 e– + 4 H
+
2 Pyruvate + 2 H2O
2 ATP + 2 H+
2 NADH
• A closer look at the
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
CH2OH
H
H
H
HO
HO
Glycolysis
H
OH
H
OH
Glucose
ATP
1
Hexokinase
ADP
CH2OH
H
H
HO
P
H
O
H
OH
H
OH
Glucose-6-phosphate
2
Phosphoglucoisomerase
CH2O
H
H
P
O
CH2OH
HO
energy investment phase
HO
H
HO
Fructose-6-phosphate
3
ATP
Phosphofructokinase
ADP
CH2
O
P
O
CH2
P
O
HO
H
OH
H
HO
Fructose1, 6-bisphosphate
4
Aldolase
5
P
O
CH2
C
Isomerase
O
CH2OH
Dihydroxyacetone
phosphate
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
H
C
O
CHOH
CH2
O
Glyceraldehyde3-phosphate
P
Citric
acid
cycle
6
2 NAD+
2
Triose phosphate
dehydrogenase
2
NADH
+ 2 H+
Pi
payoff phase
2
P
O
C
O
CHOH
CH2
1, 3-Bisphosphoglycerate
2 ADP
P
O
7
Phosphoglycerokinase
2 ATP
O–
2
C
CHOH
O
CH2
3-Phosphoglycerate
P
8
Phosphoglyceromutase
O–
2
C
C
H
O
P
O
CH2OH
2-Phosphoglycerate
9
Enolase
2 H2 O
O–
2
C
O
C
P
O
CH2
Phosphoenolpyruvate
2 ADP
10
Pyruvate kinase
2 ATP
2
O–
C
C
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
CH3
Pyruvate
O
O
• Concept 9.3: The citric acid cycle completes
the energy-yielding oxidation of organic
molecules
• The citric acid cycle
– Takes place in the matrix of the mitochondrion
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
CH3
Acetyle CoA
CO2
Coenzyme A
• 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
FAD
3 NADH
+ 3 H+
ADP + P i
ATP
Figure 9.11
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Citric Acid cycle
Citric
acid
cycle
Glycolysis
Oxidative
phosphorylation
S
CoA
C
O
CH3
Acetyl CoA
CoA
O
NADH
+ H+
SH
COO–
C
COO–
1
CH2
COO–
NAD+
Oxaloacetate
8
CH2
2
CH2
CH
Malate
HO
CH
Citrate
COO–
Isocitrate
Figure 9.12
COO–
CO2
Citric
acid
cycle
7
COO–
HC
COO–
CH2
H2O
COO–
COO–
C
HO
COO–
HO
H2O
CH2
3
NAD+
COO–
NADH
COO–
CH
Fumarate
HC
CoA
+ H+
CH2
SH
a-Ketoglutarate
CH2
COO–
6
CoA
COO–
FAD
4
SH
CH2
CH2
CH2
COO–
C
Succinate
S
Pi
GTP
ADP
ATP
9.12
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
O
COO–
COO–
5
CH2
FADH2
C
GDP
NAD+
O
CoA
Succinyl
CoA
NADH
+ H+
CO2
• Concept 9.4: During oxidative phosphorylation,
chemiosmosis couples electron transport to
ATP synthesis
• NADH and FADH2
– Donate electrons to the electron transport
chain, which powers ATP synthesis via
oxidative phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
The Pathway of Electron Transport
• In the electron transport chain
– Electrons from NADH and FADH2 lose energy
in several steps
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• At the end of the chain
– Electrons are passed to oxygen, forming water
NADH
50
Free energy (G) relative to O2 (kcl/mol)
FADH2
40
FMN
I
Fe•S
Fe•S II
O
30
Multiprotein
complexes
FAD
III
Cyt b
Fe•S
20
Cyt c1
IV
Cyt c
Cyt a
Cyt a3
10
0
Figure 9.13
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2 H + + 12 O2
H2 O
Chemiosmosis: The Energy-Coupling Mechanism
• 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• The resulting H+ gradient
– Stores energy
– Drives chemiosmosis in ATP synthase
– Is referred to as a proton-motive force
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Chemiosmosis
– Is an energy-coupling mechanism that uses
energy in the form of a H+ gradient across a
membrane to drive cellular work
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Chemiosmosis and the electron transport chain
Oxidative
phosphorylation.
electron transport
and chemiosmosis
Glycolysis
ATP
Inner
Mitochondrial
membrane
ATP
ATP
H+
H+
H+
Intermembrane
space
Protein complex
of electron
carners
Q
I
Inner
mitochondrial
membrane
IV
III
ATP
synthase
II
FADH2
NADH+
Mitochondrial
matrix
H+
Cyt c
FAD+
NAD+
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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
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
6 NADH
Citric
acid
cycle
2
Acetyl
CoA
+ 2 ATP
by substrate-level
phosphorylation
Maximum per glucose:
+ 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
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Concept 9.5: 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 ATP through
fermentation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Glycolysis
– Can produce ATP with or without oxygen, in
aerobic or anaerobic conditions
– Couples with fermentation to produce ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Types of Fermentation
• Fermentation consists of
– Glycolysis plus reactions that regenerate
NAD+, which can be reused by glyocolysis
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
P1
2 ADP + 2
Glucose
2 ATP
Glycolysis
O–
C
O
C
O
CH3
2 Pyruvate
2 NADH
2 NAD+
H
H
2
H
C
C
OH
CH3
O
CH3
2 Ethanol
2 Acetaldehyde
(a) Alcohol fermentation
P1
2 ADP + 2
Glucose
O–
Glycolysis
2 NAD+
O
C
H
2 ATP
O
OH
C
CH3
2 Lactate
(b) Lactic acid fermentation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
2 NADH
C
O
C
O
CH3
CO2
• Fermentation and cellular respiration
– Differ in their final electron acceptor
• Cellular respiration
– Produces more ATP
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Pyruvate is a key juncture in catabolism
Glucose
CYTOSOL
Pyruvate
No O2 present
Fermentation
O2 present
Cellular respiration
MITOCHONDRION
Ethanol
or
lactate
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Acetyl CoA
Citric
acid
cycle
• The catabolism of various molecules from food
Proteins
Carbohydrates
Amino
acids
Sugars
Fats
Glycerol
Glycolysis
Glucose
Glyceraldehyde-3- P
NH3
Pyruvate
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
Fatty
acids
• The control of cellular respiration
Glucose
Glycolysis
Fructose-6-phosphate
–
Inhibits
AMP
Stimulates
+
Phosphofructokinase
–
Fructose-1,6-bisphosphate
Inhibits
Pyruvate
Citrate
ATP
Acetyl CoA
Citric
acid
cycle
Oxidative
phosphorylation
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings