CAMPBELL & REECE
CHAPTER 9
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metabolic pathways that released stored
nrg by breaking down complex
molecules
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a catabolic pathway
partial degradation of sugars or other
organic fuel
anaerobic
not as efficient as aerobic respiration
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generally means aerobic
cells mostly use glucose as fuel
energy released: ATP + heat (so is
exergonic)
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nrg released:
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ΔG = -686 kcal/mol
[2870kJ]
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answer based on transfer of e- during
chemical reactions
moving e- releases nrg stored in organic
molecules which is ultimately used to
synthesize ATP
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substance giving away e- is called the
reducing agent
substance taking e- is called the oxidizing
agent
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some do not involve complete transfer of
e- (as in forming ions)
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*generally, organic molecules that have
lots of hydrogen make excellent fuels
because their bonds are source of
“hilltop” e- whose nrg will be released as
the e- “fall” down nrg gradient when
transferred to O2
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H is transferred from glucose  O2
as e- transferred nrg state of e- is
lowered
that released nrg is available for ATP
synthesis
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without EA barrier, glucose or other
foods would spontaneously combine
with O2 in air
body temperature not high enough to
initiate combustion of glucose, enzymes
required to lower EA
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glucose & other molecules are broken
down in series of steps (each w/own
enzyme)
@ key steps e- are stripped from glucose
each oxidation step involves e- traveling
with H atom  NAD+  NADH
oxidized
state
reduced
state
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Nicotinamide Adenine Dinucleotide

derivative of niacin
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enzymes called dehydrogenases remove
a pair of H atoms (with 2 e-) from
substrate (glucose) thereby oxidizing it.
dehydrogenase then delivers the 2 ealong with 1 H (1 proton) to its coenzyme
NAD+
2nd H+ is released to surroundings
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by receiving 2 e- & 1 H+, NAD+ loses its
(+) charge
NAD+ most versatile e- acceptor in
cellular respiration (used in several
redox reactions)
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When e- passed from glucose  NAD+
they lose very little of their nrg
cellular respiration uses e- transport
chain to break fall of e-  O2 into several
nrg-releasing steps
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consists of a # of molecules (proteins
mostly) in inner membrane of
mitochondria & plasma membrane of
those prokaryotes that have aerobic
respiration
@ “top” of chain NADH carries higher nrg
e- removed from glucose   “bottom”
of chain lower nrg e- passed to O2
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e- transfer from NADH  O2 is exergonic
reaction with a free energy change of :
-53 kcal/mol (-222 kJ/mol)
instead of releasing all that nrg in 1
explosive step, e- cascade down the chain
from 1 carrier molecule to next in series
of redox reactions
each carrier is more electronegative than
previous molecule
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O2 is final e- acceptor because it is the
most electronegative
can think of it as O2 pulling e- down the
chain in nrg-yielding tumble
1.
2.
3.
Glycolysis
Pyruvate Oxidation & Citric Acid Cycle
Oxidative Phosphorylation
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e- transport chain
chemiosmosis
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1.
2.
2 parts:
Energy Investment Phase
Energy Payoff Phase
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anaerobic
in cytoplasm
no CO2 released
uses 2 ATP, makes 4 ATP
2 NAD+ + 4 e- + 4H+  2 NADH + 2H+
glucose  2 pyruvate + 2 H2 O
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pyruvate  mitochondria via active
transport (eukaryotic cells)
pyruvate  stays in cytoplasm in
prokaryotes that perform aerobic
respiration
1.
2.
3.
Pyruvate’s carboxyl group (already
oxidized so has little chemical nrg) is
removed as CO2
Remaining 2 C fragment is oxidized 
acetate (ionized form of acetic acid)
with e-  NAD+  NADH
CoA (derived from vit. B) attached via S
atom to acetic acid  acetyl CoA
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aka:
Krebs Cycle
tricarboxylic acid cycle
functions as metabolic furnace that
oxidizes organic fuel derived from
pyruvate
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for each acetyl group entering cycle:
3 NAD+  3NADH
1 FAD + 2 e- + 2H+  1 FADH2
* 1 GDP + 1ATP  1GTP + 1ADP
* GTP made in many animal cell
mitochondria: GTP similar to ATP in
structure & function /example of
substrate-level phosphorylation
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@ end of Citric Acid Cycle only have 4 ATP
made (counting glycolysis)
also have NADH & FADH2 (hi nrg ecarriers) which accounts for most of nrg
extracted form glucose
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collection of molecules embedded in
inner membrane of mitochondria
(prokaryotes have them embedded in
their plasma membrane)
inner membrane has multiple folds
allowing for multiple copies of etransport chain to be working at same
time
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most of the molecules are proteins, rest
are nonprotein components necessary
for catalytic functions of certain enzymes
there is a drop in free nrg as e- move thru
e- transport chain alternating reduced
state  oxidized state
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http://www.johnkyrk.com/mitochondrion.
html
http://highered.mcgrawhill.com/sites/0072507470/student_view0
/chapter25/animation__electron_transport_
system_and_formation_of_atp__quiz_1_.html
http://www.science.smith.edu/department
s/Biology/Bio231/etc.html
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http://www.dnatube.com/video/2354/Det
ailed-ElectronTransport-Chain
http://vcell.ndsu.nodak.edu/animations/et
c/movie-flash.htm
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e- transport chain makes no ATP directly
it does break the fall of e- from food to O2
into a series of smaller steps that
releases nrg in manageable amts
for every 4 e- 1 O2 + 4 H+  2 H2 O
(O2 is final e- acceptor)
inner membrane protein ATP Synthase
makes ADP + Pi  ATP using the proton
(H+) gradient as nrg source
 chemiosmosis is the process in which nrg
stored in H+ gradient across membrane
is used to drive cellular work
(see animations)
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% of chemical nrg in glucose  ATP
oxidation of 1 mol glucose under
standard conditions = 686 kcal/mol
1 ATP stores 7.3 kcal/mol
efficiency of cellular respiration =
7.3kcal/mol x 32mol ATP/1 mol glucose÷
686 kcal/mol = 0.34  34%
actually a little higher: under cell conditions ΔG is
lower
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66% of nrg from oxidation of glucose lost
as heat
adaptation in hibernating animals:
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use brown fat: cells packed full of
mitochondria & that has a protein in inner
membrane that allows H+ to flow down its
concentration gradient w/out making ATP
(so oxidation of stored fats generates heat
w/out making ATP)
Brown Fat
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w/out this adaptation ATP would build
up to point where cellular respiration
would shut down
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1.
2.
without an adequate supply of O2
“pulling” e- thru transport chain
oxidative phosphorylation eventually
stops
2 things cells can do to get some ATP out
of organic fuel w/out O2
Anaerobic respiration
Fermentation
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uses e- transport chain (fermentation
does not)
used in anaerobic bacteria:
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have e- transport chain but O2 is not the
final e- acceptor
some marine prokaryotes use (SO4 -²) sulfate
ion as final e- acceptor  H2 S
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uses no O2 & no e- transport chain
is extension of glycolysis in cytoplasm
that generates ATP by substrate-level
phosphorylation of glycolysis & recycles
NADH back to NAD+
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1.
2.
Alcohol
pyruvate  ethanol in 2
steps:
2 pyruvate  2 CO2 + 2
acetaldehyde
2 acetaldehyde + 2
NADH  2 ethanol + 2
NAD+
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Lactic Acid
pyruvate is reduced
directly by NADH 
lactate (end product)
lactate is ionized form of
lactic acid
used by fungi & bacteria
to make cheese & yogurt
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1.
2.
3.
all 3:
produce ATP by harvesting chemical
nrg in food
use glycolysis to oxidize glucose 
pyruvate with a net production of 2 ATP
by substrate-level phosphorylation
use NAD+ as oxidizing agent
methods of oxidizinf NADH  NAD+
1. Fermentation
 pyruvate or acetaldehyde
2. Anaerobic Respiration
 e- transport chain  atom less
electronegative than O like S H2S
3. Aerobic Respiration
 e- transport chain  O2  H2O
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oxidative phosphorylation yields up to
16x more ATP/glucose molecule
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only carry out fermentation or anaerobic
respiration
O2 is toxic to them
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yeasts & many bacteria
make enough ATP to survive w/out
aerobic oxidation but if O2 available can
go thru oxidative phosphorylation
muscle fibers (cells) can behave as
faculative anaerobes
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ancient prokaryotes used glycolysis to
make ATP b/4 O2 present in atmosphere
oldest prokaryotes: 3.5 billion yrs old
2.7 billion years ago O2 in atmosphere:
source: cyanobacteria thru
photosynthesis
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Glycolysis is a metabolic “heirloom” from
early cells that continues to function in
fermentation & as 1st stage in breakdown
of organic molecules by respiration
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Glycolysis & Citric Acid Cycle lead to
many other metabolic pathways
food we eat has very little glucose in it:
glycolysis can accept other carbohydrates
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glycogen  breaks down to glucose
disaccharides  monosaccharides
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1st broken down to their a.a.
those not needed for protein synthesis
can be converted to intermediates of
glycolysis & Citric Acid Cycle
1st amino group removed (deamination)
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1st  glycerol & fatty acids
glycerol  glyceraldehyde 3-phosphate
(intermediate in glycolysis)
fatty acids  beta oxidation  2-C
fragments  Citric Acid Cycle as acetylCoA
beta oxidation process generate NADH &
FADH2  e- transport chain (reason why
lipids have more nrg stored than carbs)
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cpds formed as intermediaries in
glycolysis & Citric Acid Cycle diverted to
anabolic pathways as precursors cell
uses to synthesize what it needs (using
ATP in process)
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a.a. (can make ~12)
pyruvate  glucose
acetyl CoA  fatty acids
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cells use supply & demand principles
(does not synthesize more cpds than it
needs)
Feedback inhibition: end product of
anabolic pathway inhibits enzyme(s)
that catalyze early step of pathway
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if cell “working” harder will speed up
rate of respiration
when plenty of ATP for work cell is doing
production slows down
control achieved by regulating enzymes
@ strategic places in pathway
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enzyme in glycolysis that catalyzes
addition of 2nd phosphate group which is
1st step that commits the substrate
irreversibly to glycolytic pathway
allosteric enzyme: has receptor sites for
specific inhibitors & activators
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inhibitor is ATP
activator: AMP
is also sensitive to concentration of
citrate: when citrate builds up in
mitochondria some diffuses into
cytoplasm and acts as inhibitor
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The energy that keeps us
alive is released, not
produced, by cellular
respiration