Download 09 Respiration

Chapter 9
Cell Respiration p147
The Principle of Redox
• Redox reactions
– Transfer electrons from one reactant to another
by oxidation and reduction
• Redox reactions also occur when the movement of
electrons is not complete but involve a change in the
degree of electron sharing in covalent bonds.
• In the combustion of methane to form water and
carbon dioxide, the nonpolar covalent bonds of
methane (C-H) and oxygen (O=O) are converted
to polar covalent bonds (C=O and O-H).
Fig. 9.3
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
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
Stepwise Energy Harvest via NAD+
and the Electron Transport Chain
• Cellular respiration
– Oxidizes glucose in a series of steps
• 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–
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
NADH
H O
C
H
N
NH2
Nicotinamide
(reduced form)
+
• NADH, the reduced form of NAD+
– Passes the electrons to the electron transport
chain
• Unlike the explosive release of heat energy that
would occur when H2 and O2 combine, cellular
respiration uses an electron transport chain to
break the fall of electrons to O2 into several
steps.
Fig. 9.5
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
2. Cells recycle the ATP they use for work
• ATP, adenosine triphosphate, is the pivotal
molecule in cellular energetics.
• It is the chemical equivalent of a loaded spring.
– The close packing of three negatively-charged
phosphate groups is an unstable, energy-storing
arrangement.
– Loss of the end phosphate group “relaxes” the
“spring”.
• The price of most cellular work is the conversion
of ATP to ADP and inorganic phosphate (Pi).
• An animal cell regenerates ATP from ADP and Pi
by the catabolism of organic molecules.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
High
Energy
Bonds
High
Energy
Bonds
2 High energy bonds between
phosphate groups
Breaking a bond
releases energy
Catabolism breaks
Anabolism builds
down molecules
up molecules
ex: aerobic respiration
ex: muscle building
• The transfer of the terminal phosphate group
from ATP to another molecule is
phosphorylation.
– This changes the shape of the receiving molecule,
performing work (transport, mechanical, or
chemical).
– When the
phosphate
groups leaves
the molecule,
the molecule
returns to its
alternate
Fig. 9.2
shape.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
The Stages of Cellular
Respiration: A Preview
• Respiration is a cumulative function of
three metabolic stages
– Glycolysis
– The citric acid cycle
– Oxidative phosphorylation
• Glycolysis
– Breaks down glucose into two molecules of
pyruvate
• The citric acid cycle
– Completes the breakdown of glucose
• Oxidative phosphorylation
– Is driven by the electron transport chain
– Generates ATP
Electrons carried
via NADH and
FADH2
Electrons
carried
via NADH
• An overview of cellular respiration
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
Transparency 7A-1
Transparency 7A-2
Transparency 7A-3
Transparency 7A-4
Transparency 7A-5
Transparency 7A-6
Oxidative
Phosphorylation
Transparency 7A-6
Oxidative
Phosphorylation
1. What is the source of carbon for cellular respiration?
Glucose (C6H12O6) is the carbon source.
Transparency 7A-7
Oxidative
Phosphorylation
2. Where do Stages 2 and 3 of cellular respiration take place?
in mitochondria
Fig. 9.9a
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Feedback
Inhibition
• The net yield from glycolysis is 2 ATP and 2
NADH per glucose.
– No CO2 is produced during glycolysis.
• Glycolysis occurs whether O2 is present or not.
– If O2 is present, pyruvate moves to the Krebs cycle
and the energy stored in NADH can be converted to
ATP by the electron transport system and oxidative
phosphorylation.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Glycolysis Animation
Bridge to the Krebs Cycle
• As pyruvate enters the mitochondrion, a
multienzyme complex modifies pyruvate to
acetyl CoA which enters the Krebs cycle in the
matrix.
– A carboxyl group is removed as CO2.
– A pair of electrons is transferred from the remaining
two-carbon fragment to NAD+ to form NADH.
– The oxidized
fragment, acetate,
combines with
coenzyme A to
form acetyl CoA.
Fig. 9.10
Bridge to the
Krebs Cycle
Krebs
Cycle
2 NADH
(pyruvate)
2 NADH
6 NADH
2 FADH2
Proteins of the Electron
Transport Chain (ETC)
are located in the inner
mitochondial membrane
called the cristae
• Electrons carried by
NADH are transferred
to the first molecule in
the electron transport
chain, flavoprotein.
– The electrons continue
along the chain which
includes several
cytochrome proteins
and one lipid carrier.
• The electrons carried
by FADH2 have lower
free energy and are
added to a later point in
the chain.
Fig. 9.13
The flow of electrons in
the ETC provide energy
to pump protons to the
outer compartment –
forming a proton
gradient
(inner Matrix)
• A protein complex,
ATP synthase, in the
cristae actually makes
ATP from ADP and Pi.
• ATP used the energy of
an existing proton
gradient to power ATP
synthesis.
– This proton gradient
develops between the
intermembrane space
and the matrix.
Fig. 9.14
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• The proton gradient is produced by the
movement of electrons along the electron
transport chain.
• Several chain molecules can use the exergonic
flow of electrons to pump H+ from the matrix to
the intermembrane space.
– This concentration of H+ is the proton-motive
force.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
H+
H+
H+
H+
Proton pumps
make a chemical
and electrical
gradient that is
used to make
ATP – this is
chemiosmosis
• The ATP synthase molecules are the only place
that will allow H+ to diffuse back to the matrix.
• This exergonic flow of H+ is used by the
enzyme to generate ATP.
• This coupling of the redox reactions of the
electron transport chain to ATP synthesis is
called chemiosmosis.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• The mechanism of ATP
generation by ATP
synthase is still an area
of active investigation.
– As hydrogen ions flow
down their gradient, they
cause the cylinder portion
and attached rod of ATP
synthase to rotate.
– The spinning rod causes a
conformational change in
the knob region,
activating catalytic sites
where ADP and inorganic Fig. 9.14
phosphate combine to
ATP.
Copyrightmake
© 2002 Pearson
Education, Inc., publishing as Benjamin Cummings
• Chemiosmosis is an energy-coupling mechanism
that uses energy stored in the form of an H+
gradient across a membrane to drive cellular
work.
– In the mitochondrion, chemiosmosis generates ATP.
– Chemiosmosis in chloroplasts also generates ATP,
but light drives the electron flow down an electron
transport chain and H+ gradient formation.
– Prokaryotes generate H+ gradients across their
plasma membrane.
• They can use this proton-motive force not only to generate
ATP but also to pump nutrients and waste products across
the membrane and to rotate their flagella.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Mitchell
Hypothesis
Fig. 9.16
• How efficient is respiration in generating ATP?
– Complete oxidation of glucose releases 686 kcal per
mole.
– Formation of each ATP requires at least 7.3
kcal/mole.
– Efficiency of respiration is 7.3 kcal/mole x 38
ATP/glucose/686 kcal/mole glucose = 40%.
– The other approximately 60% is lost as heat.
• Cellular respiration is remarkably efficient in
energy conversion.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
2 ATP
2 ATP
34 ATP
2 FADH2
2 NADH
2 NADH
6 NADH
2 CO2
4 CO2
Electron Transport
System
Fermentation
Glycolysis
Krebs Cycle
½ O2
1. Fermentation enables some cells to
produce ATP without the help of oxygen
• Oxidation refers to the loss of electrons to any
electron acceptor, not just to oxygen.
– In glycolysis, glucose is oxidized to two pyruvate
molecules with NAD+ as the oxidizing agent, not O2.
– Some energy from this oxidation produces 2 ATP
(net).
– If oxygen is present, additional ATP can be generated
when NADH delivers its electrons to the electron
transport chain.
• Glycolysis generates 2 ATP whether oxygen is
present (aerobic) or not (anaerobic).
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
NADH
NAD+
The ETC regenerates NAD+ to be recycled back to
Glycolysis. The ETC can only do this if O2 is available
Without NAD+, Glycolysis cannot occur.
NAD+ must be
regenerated for
glycolysis to continue
34
NAD+ recycled
If no O2 is
available NAD+ is
made by having
NADH dump its
electrons on to
pyruvate.
ecycled
NAD+ is
recycled
back to
glycolysis
Because
NAD+ is
recycled most
of the energy
from
Glycolysis is
lost
• In alcohol fermentation, pyruvate is converted
to ethanol in two steps.
– First, pyruvate is converted to a two-carbon
compound, acetaldehyde by the removal of CO2.
– Second, acetaldehyde is reduced by NADH to
ethanol.
– Alcohol fermentation
by yeast is used in
brewing and
winemaking.
Fig. 9.17a
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• During lactic acid fermentation, pyruvate is
reduced directly by NADH to form lactate
(ionized form of lactic acid).
– Lactic acid fermentation by some fungi and bacteria
is used to make cheese and yogurt.
– Muscle cells switch from aerobic respiration to
lactic acid fermentation to generate ATP when O2 is
scarce.
• The waste product,
lactate, may cause
muscle fatigue, but
ultimately it is
converted back to
pyruvate in the liver.
Fig. 9.17b
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Different food
molecules can
enter and exit at
different levels in
the aerobic
pathway
ATP acts as negative modulator
inactivating the first enzyme
Regulation such as
feedback inhibition
controls how much
ATP is produced
1/2 second
<1 Minute
1-3 Minutes
>3 Minutes
Other molecules
besides glucose
can be used in
the aerobic
pathway
Chapter 9
Cellular Respiration: Harvesting
Chemical Energy
Respiration
Occurs 2 ways
With oxygen
Has 3 stages
Without oxygen
Has two stages
1st
1st
2nd
2nd
Which produces
3rd
Which produces
waste products
• When electrons flow along the electron
transport chains of mitochondria, which of
the following changes occur?
–
–
–
–
The pH of the matrix increases.
ATP synthase pumps protons by active transport.
The electrons gain free energy.
The cytochromes of the chain phosphorylate ADP
to form ATP.
– NAD+ is oxidized.
• In the presence of a metabolic poison that
specifically and completely inhibit the function
of mitochondrial ATP synthase, which of the
following would you expect?
– a decrease in the pH difference across the inner
mitochondrial membrane
– an increase in the pH difference across the inner
mitochondrial membrane
– increased synthesis of ATP
– oxygen consumption to cease
– proton pumping by the electron transport chain to
cease
• In the 1940s, some physicians prescribed low doses of
a drug called dinitrophenol (DNP) to help patients lose
weight. This unsafe method was abandoned after a few
patients died. DNP uncouples the chemiosmotic
machinery by making the lipid bilayer of the inner
mitochondrial membrane leaky to H+. What impact
does this have on ATP production? *
–
–
–
–
–
reduces substrate level phosphorylations
increases substrate level phosphorylations
reduces oxidative level phosphorylations
increase oxidative level phosphorylations
This would have no impact on ATP production.
• Cyanide is a poison that blocks the passage of
electrons along the electron transport chain. Which of
the following is a metabolic effect of this poison?
– The lower pH of the intermembrane space is much lower
than normal.
– Electrons are passed directly to oxygen, causing cells to
explode.
– Alcohol would build up in the cells.
– NADH supplies would be exhausted, and ATP synthesis
would cease.
– No proton gradient would be produced, and ATP synthesis
would cease.
• Which kind of metabolic poison would most
directly interfere with glycolysis?
– an agent that reacts with oxygen and depletes
its concentration in the cell
– an agent that binds to pyruvate and inactivates
it
– an agent that closely mimics the structure of
glucose but is not metabolized
– an agent that reacts with NADH and oxidizes it
to NAD+
– an agent that inhibits the formation of acetyl
coenzyme A
• Glucose, made from six radioactively labeled
carbon atoms, is fed to yeast cells in the absence
of oxygen. How many molecules of radioactive
alcohol (C2H5OH) are formed from each
molecule of glucose?
–
–
–
–
–
0
1
2
3
6
•
A young relative of yours has never had much energy. He goes
to a doctor for help and is sent to the hospital for some tests.
There they discover his mitochondria can use only fatty acids
and amino acids for respiration, and his cells produce more
lactate than normal. Of the following, which is the best
explanation of his condition?
–
–
–
–
–
His mitochondria lack the transport protein that moves pyruvate across
the outer mitochondrial membrane.
His cells can not move NADH from glycolysis into the mitochondria.
His cells contain something that inhibits oxygen use in his
mitochondria.
His cells lack the enzyme in glycolysis that forms pyruvate.
His cells have a defective electron transport chain, so glucose goes to
lactate instead of to acetyl CoA.
• You have a friend who lost 15 pounds of fat on a
diet. Where did the fat go (how was it lost)? *
– It was released as CO2 and H2O.
– Chemical energy was converted to heat and then
released.
– It was converted to ATP, which weighs much less than
fat.
– It was broken down to amino acids and eliminated
from the body.
– It was converted to urine and eliminated from the
body.
Review Questions Links
•
•
•
•
Link 1
Link 2
Link 3
Link 4
WORKSHEET ELODEA/FISH
1. Write the equation of the reaction of CO2 and water.
2. Bromothymol blue (BTB) is colored blue when the pH is __________.
3. BTB is colored green when the pH is ____________________.
4. BTB is colored yellow when the pH is _______________.
5. A high conc. of CO2 will cause the pH of the water to be______.
What color will the BTB be?
6. The gas that is released by consumers is ___________.
7. The gas that is produced by producers is ___________.
8. The gas that is absorbed by producers is ___________.
9. A low level of CO2 will cause the pH of water to be _______.
What color will the BTB be?
10. Explain the color of the BTB in the bowl 2 that just had the fish
(Use the terms pH, CO2 and acid).
11. Was the fish healthy in bowl 2? Why?
12. Explain the color of the BTB in the bowl 3 that just had the plant.
13. Is the plant healthy in bowl 3? Why?
14. Explain the color of the bowl 4 that had both the fish and the plant.
(Use the terms pH, acid, CO2, photosynthesis, respiration).
15. Do you think the plant and fish were healthy in bowl 4? Why?
BOWL 1: WATER + BTB
BOWL 2: WATER + BTB + FISH
BOWL 3: WATER + BTB + PLANT
BOWL 4: WATER + BTB + FISH + PLANT