Chapter Summary: The Big Picture (1)
• Chapter foci:
– Chemical bonds and ion gradients are cellular
energy
– Membrane transport proteins play a role in energy
transduction
– Energy transduction pathways in the chloroplast
– Energy transduction in the mitochondria with an
emphasis on glucose metabolism
– Energy transduction in bacteria are diverse
Chapter Summary: The Big Picture (2)
• Section topics:
– Cells store energy in many forms
– Gradients across cellular membranes are essential
for energy storage and conversion
– Storage of light energy occurs in the chloroplast
– Cells use a combination of channel, carrier, and
pump proteins to transport small molecules across
membranes
– The first phase of glucose metabolism occurs in the
cytosol
– Aerobic respiration results in the complete oxidation
of glucose
Physiological
status
Source of energy loss
Survival
*Retain
viability
Repair damage to key
macromolecules
Maintenance
*Sustain activity
Repair/replace of cellular material
Motility
Inefficiency/heat generation
Futile ion cycling
Secretion
Growth
*Replication
All of the above, and:
Replication of cellular material
logE
survival: maintenance: growth 1:103:106
1-4 =100% efficient
E: cellular energy supply
Fs: substrate flux (FS),
G'rxn: free energies for
catabolism
G'ATP: free energy for ATP
synthesis
ADP + Pi = ATP (60 kJ mol-1)
-n: translocated H+ for ATP
synthesis
E < ME= inactivity or death
ME: maintenance energy
Cells store energy in many forms
• Key Concepts (1):
– Energy exists in three forms: kinetic, potential, and
heat.
– The laws of thermodynamics define the rules for
energy transfer.
– Cells remain alive by converting environmental
energy sources into cell-accessible energy forms.
– High-energy electrons and ion gradients are the most
common forms of cellular energy storage.
– The amount of energy in an ion gradient is
expressed as an electrical potential.
.
Cells store energy in many forms
• Key Concepts (1):
– Cells remain alive by converting environmental
energy sources into cell-accessible energy forms.
.
O2
CO2
H2O
Cells store energy in many forms
• Key Concepts (1):
*High-energy electrons
and ion gradients are the
most common forms of
cellular energy storage.
*The amount of energy
in an ion gradient is
expressed as an
electrical potential.
.
The laws of thermodynamics define the
rules for energy transfer
• H2S released through volcanic
activity
• H2S dissolves in H2O and reacts
with metals to form precipitates
• 2 S-2 + Fe+2  FeS2 (pyrite)
• SO2-2 + Ca+2  CaSO4 (gypsum)
Fats and polysaccharides are
examples of long-term energy storage
in cells
High-energy electrons and ion
gradients are examples of short-term
potential energy
How cells store potential energy with
gradients
ATP + H2O =ADP + Pi DGo’ =-30.5KJ/mole
ADP + H2O= AMP + Pi DGo’ = -28.4KJ/mole
• Cells couple energetically favorable and
unfavorable reactions
• Nucleotide triphosphates store energy for
immediate use
• The amount of potential energy stored in an ion
gradient can be expressed as an electrical potential
Gradients across cellular membranes are
essential for energy storage and
conversion
• Key Concepts:
– Membrane transport proteins are responsible for
moving ions through the phsopholipid bilayer of
cellular membranes.
– Membrane transport proteins are organized into
three groups: channels, carriers, and pumps.
– All channels dissipate gradients, all pumps build
gradients, and most carriers only dissipate
gradients. Some carriers can build gradients as well,
using indirect active transport.
Phospholipid bilayers are semipermeable barriers
Figure 10.01: Permeation of lipid bilayers by biologically important molecules.
Protein channels, carriers, and
pumps regulate transport of small
molecules across membranes
• Protein channels
dissipate gradients
Figure 10.02: Different views of a Cl- transporter. Note how
several transmembrane alpha helices combine to form the
pore, including the selectivity filter.
Channel types
Ligand-gated
Voltage-gated
Figure 10.03: Three methods for controlling
the opening and closing of channels. Ca+2
channels are used as examples.
Figure 10.04: Three models for how
voltage across a membrane controls the
shape of voltage-gated channels.
Different types of K+ channels are shown
as examples.
Passive carrier proteins dissipate
gradients
Figure 10.05: A comparison of channel and
carrier proteins.
Figure 10.06: An example of a
conformation change in a carrier
protein.
Symport and Antiport
Figure 10.07: Some examples of Na+-dependent
transporters.
Energy-coupled carrier proteins
(pumps) build gradients
Direct active transport
Figure 10.08: The relationship
between direct and indirect active
transport.
Indirect active transport
PUMPS, CHANNELS AND TRANSPORTERS
Transporters
Membrane Transporter Proteins: Classification
Primary active transport:
Transport depends on the energy from the
hydrolysis of ATP
Secondary active transport:
Use of energy from a secondary diffusion gradient set
up across the membrane using another ion. Because
this secondary diffusion gradient initially established
using an ion pump, as in primary active transport, the
energy is ultimately derived from the same source-ATP
hydrolysis.
Membrane Transporter Proteins: Classification
Facilitated diffusion:
Transport from higher concentration to lower
concentration. It does not require the expenditure
of metabolic energy
Channels
Selective transport water or ions down
their concentration or electric potential
gradients
Highly regulated
Energetically favorable reaction
A passageway across the membrane
through which multiple water molecules
or ions move simultaneously at a very
rapid rate—up to 108 per second
Transporters: Uniporters
Transport is specific and saturable
Facilitated “low resistance” diffusion:
Down the concentration gradient
Reversible
Rate much higher than passive diffusion
Transporters:
Secondary transporters
Couple the movement of one type of ion or
molecule against its concentration gradient to
the movement of a different ion or molecule
down its concentration gradient
Mediate coupled reactions in which an
energetically unfavorable reaction coupled to
energetically favorable reaction
Transporters:
Secondary transporters
Catalyze “uphill” movement of certain molecules
often referred to as “active transporters”, but
unlike pumps, do not hydrolyze ATP (or any
other molecule) during transport
Pumps
P, F, and V classes transport ions only, whereas the
ABC superfamily class transports small molecules
as well as ions.
Pumps
Use the energy of ATP hydrolysis to move ions or
small molecules across a membrane against a
chemical concentration gradient or electric
potential.
Overall reaction—ATP hydrolysis and the “uphill”
movement of ions or small molecules—is
energetically favorable
Storage of light energy occurs in the
chloroplast
• Key Concepts (1):
– Chloroplasts capture kinetic energy in photons of
sunlight and convert it into an ion gradient and
high energy electrons, which are stored on the
electron carrier NADPH.
– The machinery that converts sunlight into these
energy forms is a cluster of proteins in the
thylakoid membrane inside chloroplasts.
Collectively, they are known as the thylakoid
electron transport chain.
Storage of light energy occurs in the
chloroplast
• Key Concepts (2):
– The ion gradient energy is converted into ATP by
an enzyme called ATP synthase.
– The energy in ATP and NADPH is used to
convert atmospheric CO2 into carbon-containing
macromolecule called glyceraldehydes 3phosphate via set of chemical reactions called
the Calvin cycle.
Chloroplasts have
three membrane-bound
compartments
Chloroplasts convert sunlight into the
first forms of cellular energy
• Light reactions - energy transduction reactions
• Dark reactions - carbon assimilation reactions
The energy transduction (light) reactions
sunlight
into
stored
potential
convert
energy
The electron transport chain
in the thylakoid membrane.
The “Z” scheme
The carbon assimilation (dark)
reactions convert stored potential
energy into macromolecules
Figure 10.13: An overview of the Calvin cycle.
Figure 10.14: The synthesis of
glucose and sucrose from G3P in
the cytosol.
The carbon assimilation (dark)
reactions convert stored potential
energy into macromolecules
The synthesis of glucose and
sucrose from G3P in the cytosol.
Cells use combination of channel, carrier, and
pump proteins to transport small molecules
across membranes
• Key Concepts:
– The majority of the macromolecules made by cells
can serve as food energy for other cells. To access
this energy, the chemical bonds holding these
macromolecules must be broken.
– In animals, macromolecules are broken into cellular
building blocks (via digestion) in the extracellular
space.
– Cellular building blocks (e.g., glucose) are
transported across the plasma membrane by an
integrated system of channels, carriers, and
pumps.
leaky K+ channel,
Na+/glucose
symporter, and
passive glucose
carrier work
together to move
glucose from gut
lumen to
bloodstream
Macromolecule
Transport
The cholera toxin: when things go wrong
A
with membrane function
cholera
toxin
Lumen
Gs
Cytosol
G protein
1.Cholera toxin subunit A crosses
the membrane and activates a G protein
A
Lumen
Cytosol
Gs
AC
ATP
cAMP
2. G protein activates adenyl cyclase
to produce cAMP
Lumen
Cytosol
K+
Cl- Na+
HCO3-
3. cAMP activates a Cl- channel.
K+, Na+ Cl- and HCO3- are secreted to the
intestinal lumen. The lumen osmotic
pressures rises
Lumen
Cytosol
K+
ClNa+
HCO3-
water
flow
4. A large osmotic pressure gradient
is established between the cytosol and
the lumen causing large amounts of water
to go to the lumen. This produces diarrhea
and dehydration
Oral rehydration: Gatorade
glucose
Water flow
Na+
Lumen
Lumen
Na+/glucose
symporter
Cytosol
Cytosol
5. :
The Na+/glucose symporter binds Na+ and glucose in
the lumen and transports both to the cytosol.
This increases the osmotic pressure in the cell making water
return to cell by osmosis
The first phase of glucose metabolism
occurs in the cytosol
• Key Concepts (1):
– The steps taken to extract energy from glucose
are very similar to the steps chloroplasts use to
build glucose from G3P, only in reverse order.
– The first 10 enzymatic steps in the digestion of
glucose are called glycoslysis.
The first phase of glucose metabolism
occurs in the cytosol
• Key Concepts (2):
– The products of glycolysis include the molecule
pyruvate, which must be metabolized to keep
glycolysis from stalling.
– In the absence of molecular oxygen (O2),
pyruvate is metabolized by a process called
fermentation. Two different methods of
fermentation have evolved in different organisms.
Glycolysis is subdivided into 3 stages
• The 10 chemical
reactions in glycolysis
convert glucose into 2three-carbon
compounds (pyruvate),
two NADH molecules,
and two ATP molecules
In the absence of O2, pyruvate undergoes
fermentation
Figure 10.18: Three fates of pyruvate.
In the absence of O2, pyruvate undergoes
fermentation
Figure 10.18: Three fates of pyruvate.
Aerobic respiration results in the complete
oxidation of glucose
• Key Concepts (1):
– The appearance of molecular oxygen in the
atmosphere allowed some organisms to harness the
strong electronegativity of oxygen atoms to extract
18-fold more ATP energy than glycolysis alone.
– Aerobic respiration takes place in mitochondria, and
occurs in four stages.
– Stage one converts pyruvate into acetyl CoA, the
substrate of a metabolic cycle called the Krebs cycle
(stage two).
– The Krebs cycle resembles the Calvin cycle run in
reverse.
Aerobic respiration results in the complete
oxidation of glucose
• Key Concepts (2):
5) During stage three, the high-energy electrons
removed from pyruvate and acetyl CoA are passed
through an electron transport chain in inner
mitochondrial membrane, similar to thylakoids. At the
end of the electron transport chain, the electrons are
returned to oxygen atom to rebuild the water molecule
that was oxidized at the beginning of photosynthesis,
thereby completing the cyclic journey of electrons.
6) In stage four, the proton gradient formed by the
electron transport chain is converted into ATP by and
ATP synthase.
Aerobic respiration occurs in 4 stages (1)
• Stage 1: Pyruvate is
transported into
mitochondrial matrix
and converted into
acetyl CoA
Aerobic respiration occurs in 4 stages (1)
• Stage 2: Acetyl CoA is
fully oxidized to CO2,
GTP, and high-energy
electron carriers
Overview of mitochondrial respiration
Yield of the glycolysis-aerobic metabolism
pathway
Aerobic respiration occurs in 4 stages (2)
• Stage 3: The electron
transport chain (ETC)
uses high-energy
electrons from NADH
and FADH2 to build a
proton gradient
across the inner
mitochondrial
membrane
• Stage 4: The F1/Fo
ATP synthase uses
the proton gradient to
make ATP
ETC
Figure 10.21: The mitochondrial electron transport chain.
The redox potential of reactants indicates the energy level
of the electrons moving through the mitochondrial
electron transport chain.
A model of the F1Fo ATPase.
Final accounting of the ATP yield from
aerobic metabolism
One molecule of glucose oxidized by aerobic
respiration yields the following:
Glycolysis
2 ATP from substrate-level phosphorylation
2 NADH yields 6 ATP
Transition Reaction
2 NADH yields 6 ATP by oxidative
phosphorylation
Citric Acid Cycle
-2 ATP from substrate-level phosphorylation 6
NADH yields 18 ATP by oxidative
phosphorylation 2 FADH2 yields 4 ATP by
oxidative phosphorylation
Total Theoretical Maximum Number of ATP
Generated per Glucose : 38 ATP
4 from substrate-level phosphorylation;
34 from oxidative phosphorylation.
In eukaryotic cells, the maximum yield of ATP
generated per glucose is 36 to 38 depending
on how the 2 NADH during glycolysis enter the
mitochondria and whether the resulting yield
is 2 or 3 ATP per NADH.
Glycerol phosphate shuttle
• In muscle and brain
• Each NADH
converted to
FADH2 inside
mitochondrion
– Produces 2 ATP
The life of aerobic organisms depends on primary energy transduction
Diversity of bacterial
respiratory
complexes
SUBSTRATES
DEHYDROGENASES
QH2
bc1
complex
cyt
c
cyt aa3
Mitochondria
bc1
complex
bc1
complex
cyt
c
cyt
c
cyt
ba3
cyt
caa3
cyt
cbb3
T. thermophilus
cyt
bd
cyt bd
(II)
cyt
bo3
cyt
bd
V. cholerae E.coli
Bacterial proteins can be used as models for
eukaryotic proteins, since the prokaryotic proteins
are simpler. Also, there are more molecular
techniques that can be applied to prokaryotes.
Bacterial Complex I: 12-16 subunits,
550 kDa. Core subunits are conserved.
Mitochondrial complex I: 43 subunits
> 900kDa
AEROBIC AND AND ANAEROBIC RESPIRATION
Fermentations in bacteria
Examples of fermentation reactions