chapter 07 - dr. bill tyler's website -...
TRANSCRIPT
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Chapter 07
http://www.mobento.com/video/DiyoEA5Mc
Cellular Respiration
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**Important study hints**
• Draw out processes on
paper and label
structures and steps
• Keep working on those
flash cards!
2 http://getyournotes.blogspot.com/2012/01/cellular-respiration-aerobic-and.html
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Respiration
• Organisms can be classified
based on how they obtain energy:
– Autotrophs
• Able to produce their own organic
molecules through photosynthesis
– Heterotrophs
• Live on organic compounds
produced by other organisms
• All organisms use cellular
respiration to extract energy
from organic molecules
http://en.wikipedia.org/wiki/Heterotroph
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Cellular respiration
• Cellular respiration is a series of
reactions…
– Oxidation – loss of electrons
– Reduction – gain of electron
– Dehydrogenation – lost electrons
are accompanied by protons
• A hydrogen atom is lost (1 electron,
1 proton)
http://chemwiki.ucdavis.edu/Analytical_Chemistry/Electrochemistry/Redox_Chemistry/Oxidizing_and_Reducing_Agents
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Redox
• During redox reactions, electrons carry
energy from one molecule to another
– Redox reactions are often coupled with an
electron carrier (NAD+)
http://chemwiki.ucdavis.edu/Analytical_Chemistry/Electrochemistry/Redox_Chemistry/Oxidizing_and_Reducing_Agents
Reduced compound A
(reducing agent)
Oxidized compound B
(oxidizing agent)
B is reduced A is oxidized
A
A
B
B
e- e-
e- e-
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Redox
• Nicotinamide adenosine dinucleotide (NAD+)
– An electron carrier
– NAD+ accepts 2 electrons and 1 proton from
another molecule to become NADH
– Reaction is reversible
Product
Enzyme
NAD+
NAD+ NADH NADH
2e–
H+
+H+
Energy-rich
molecule
NAD+
Reduction
Oxidation
H H
H H
H H
H H
As energy-rich
molecule is
oxidized,
NAD+ is
reduced to
NADH
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Product
Enzyme
NAD+
NAD+ NADH NADH
2e–
H+
+H+
Energy-rich
molecule
NAD+
1. Enzymes that use NAD+
as a cofactor for oxidation
reactions bind NAD+ and the
substrate.
2. In an oxidation–reduction
reaction, 2 electrons and
a proton are transferred
to NAD+, forming NADH.
A second proton is
donated to the solution.
3. NADH diffuses away
and can then donate
electrons to other
molecules.
Reduction
Oxidation
H H
H H
H
H
H H
As energy-rich molecule is oxidized,
NAD+ is reduced to NADH
Note change
from textbook
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• In overall cellular energy harvest
– Dozens of redox reactions take place
– Number of electron acceptors, including NAD+
• In the end, high-energy electrons from initial
chemical bonds have lost much of their energy
– Electrons are transferred to a final electron acceptor
8
AH
A
NAD+
NADH
BH
B
Oxidation Oxidation Reduction Reduction
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• Aerobic respiration
– Final electron receptor is oxygen (O2)
• Anaerobic respiration
– Final electron acceptor is an inorganic molecule (not O2)
• Fermentation
– Final electron acceptor is an organic molecule, such as lactic acid or ethanol
Types of Cellular Respiration
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Aerobic respiration
C6H12O6 + 6O2 6CO2 + 6H2O
• Free energy = – 686 kcal/mol of glucose
– Free energy can be even higher than this in a cell
– This large amount of energy must be released in small steps rather than all at once.
– C6H12O6 (general form for 6 carbon sugar such as glucose)
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2e–
Electrons from food
High energy
Low energy
2H+ 1 / 2 O2
Energy released
for ATP synthesis
H2O
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Electron carriers
• Many types of carriers used
– Soluble, membrane-bound, move within
membrane
• All carriers can be easily oxidized and
reduced
– Some carry just electrons, some electrons
and protons
– NAD+ acquires 2 electrons and a proton to
become NADH
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
H H
O
NH2 + 2H
CH2 O
O
O
H
H
NH2
H
H
N
N
N
CH2 O
O
O
H
H
NH2
O–
H
H
N N
N
H H O
N
N
H H
H
C C
O P
O P O– O P
O– O P
N N
OH
CH2
NADH: Reduced form of nicotinamide
O
O O
O
NAD+: Oxidized form of nicotinamide
Reduction
Oxidation
Adenine Adenine
OH OH
OH OH OH
OH OH
NH2 + H+
CH2
O–
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ATP
• Cells use ATP to drive endergonic
reactions
– ΔG (free energy) = –7.3 kcal/mol
– Compare with ΔG from complete
combustion of glucose = –686 kcal/mol
http://fgamedia.org/faculty/cholcroft/Bio45/miscellaneous_web_pages/Lectures/Metabolism/Metabolism_Intro.html
Cellular reactions can’t use all
the energy of glucose breakdown
at once, so cells must use
stepwise breakdown and
intermediaries such as ATP
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• 2 mechanisms for ATP synthesis
1. Substrate-level phosphorylation
• Transfer phosphate group directly from substrate
molecule to ADP
• During glycolysis and Krebs cycle
2. Oxidative phosphorylation
• ATP synthase uses energy from a proton gradient
in the electron transport chain
PEP
– ADP
Enzyme Enzyme
– ATP P P
P
Adenosine
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
PEP
– ADP
Enzyme Enzyme
– ATP P
P
P
Adenosine
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Oxidation of Glucose
The complete oxidation of
glucose proceeds in
stages:
1. Glycolysis
2. Pyruvate oxidation
3. Krebs cycle
4. Electron transport
chain & chemiosmosis
http://www.mobento.com/video/DiyoEA5Mc
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Outer
mitochondrial
membrane
Intermembrane
space
Mitochondrial
matrix
FAD O2
Inner
mitochondrial
membrane
Electron
Transport Chain Chemiosmosis
ATP Synthase
NAD+
Glycolysis
Pyruvate
Glucose
Pyruvate
Oxidation
Acetyl-CoA
Krebs
Cycle
CO2
ATP H2O
ATP
e–
e–
NADH
NADH
CO2
ATP
NADH
FADH2
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H+
e–
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Glycolysis • Converts 1 glucose (6 carbons) to 2
pyruvate (3 carbons)
• 10-step biochemical pathway
• Occurs in the cytoplasm
• 2 NADH produced by the reduction of NAD+
• Net production of 2 ATP molecules by substrate-level phosphorylation – (uses 2 ATPs and produces 4 total = 2
net ATPs)
• Fun fact – Only process that occurs in red blood
cells since they do not have mitochondria!
ATP
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Glycolysis
NADH
Pyruvate Oxidation
ATP
Electron Transport Chain
Chemiosmosis
Krebs
Cycle
6-carbon sugar diphosphate
NAD+ NAD+
Pri
min
g R
ea
cti
on
s
Cle
ava
ge
O
xid
ati
on
an
d A
TP
Fo
rma
tio
n
NADH NADH
P P
P P
ATP ATP
ADP ADP
3-carbon sugar
phosphate
3-carbon sugar
phosphate
Pi Pi
ADP ADP
ATP ATP
ATP
ADP ADP
ATP
3-carbon
pyruvate
3-carbon
pyruvate
6-carbon glucose
(Starting material)
Glycolysis begins
with the addition of
energy. Two high-
energy phosphates
(P) from two
molecules of ATP
are added to the
6-carbon molecule
glucose, producing
a 6-carbon
molecule with two
phosphates.
Then, the 6-carbon
molecule with two
phosphates is split in
two, forming two
3-carbon sugar
phosphates.
An additional
Inorganic phosphate
( Pi ) is incorporated
into each 3-carbon
sugar phosphate. An
oxidation reaction
converts the two
sugar phosphates
into intermediates
that can transfer a
phosphate to ADP to
form ATP. The
oxidation reactions
also yield NADH
giving a net energy
yield of 2 ATP and 2
NADH.
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
NADH
NAD+
NADH
Pi NAD+
Glucose
Hexokinase
Phosphofructokinase
Glucose 6-phosphate
Fructose 6-phosphate
Fructose 1,6-bisphosphate
Isomerase Aldolase
Pyruvate Pyruvate
Enolase
Pyruvate kinase
AD P
10
Glu
co
se
Gly
ce
rald
eh
yd
e
3-p
ho
sp
ha
te
Pyru
va
te
Glycolysis: The Reactions Glycolysis
NADH
Pyruvate Oxidation
H2O
ATP
ADP
Electron Transport Chain
Chemiosmosis
Krebs
Cycle
ATP
ATP
Phosphoglucose
isomerase
Glyceraldehyde 3-
phosphate (G3P)
Dihydroxyacetone
phosphate
1. Phosphorylation of
glucose by ATP.
2–3. Rearrangement,
followed by a second
ATP phosphorylation.
4–5. The 6-carbon molecule
is split into two 3-carbon
molecules—one G3P,
another that is converted
into G3P in another
reaction.
6. Oxidation followed by
phosphorylation produces
two NADH molecules and
two molecules of BPG,
each with one
high-energy phosphate
bond.
7. Removal of high-energy
phosphate by two ADP
molecules produces two
ATP molecules and leaves
two 3PG molecules.
8–9. Removal of water yields
two PEP molecules, each
with a high-energy
phosphate bond.
10. Removal of high-energy
phosphate by two ADP
molecules produces two
ATP molecules and two
pyruvate molecules.
1,3-Bisphosphoglycerate
(BPG) 1,3-Bisphosphoglycerate
(BPG)
Glyceraldehyde
3-phosphate
dehydrogenase
Pi
ADP
Phosphoglycerate
kinase
ADP
ATP
3-Phosphoglycerate
(3PG)
3-Phosphoglycerate
(3PG)
2-Phosphoglycerate
(2PG)
2-Phosphoglycerate
(2PG)
H2O
ATP
Phosphoenolpyruvate
(PEP)
Phosphoenolpyruvate
(PEP)
ADP ADP
ATP ATP
Ph
os
ph
oe
no
l-
pyru
va
te
3-P
ho
sp
ho
-
gly
ce
rate
1,3
-Bis
ph
os
ph
o-
gly
ce
rate
Glu
co
se
6-p
ho
sp
ha
te
Fru
cto
se
6-p
ho
sp
ha
te
Fru
cto
se
1,6
-bis
ph
os
ph
ate
Dih
yd
rox
ya
ce
ton
e
Ph
os
ph
ate
2-P
ho
sp
ho
-
gly
ce
rate
CH2OH
O
CH2 O
O
P
CH2 O
O
P
CH2OH
O CH2 CH2 O
O
P P
CHOH
H
C O
CH2 O P
C O
O CH2 P
CH2OH
CHOH
O C O
CH2 O
P
P
CHOH
O–
C O
CH2 O P
H C O
O–
C O
CH2OH
P
C O
O–
C O
CH2
P
C O
O–
C O
CH3
8
9
10
7
4 5
3
2
1
6
Phosphoglyceromutase
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NADH must be recycled
• For glycolysis to continue, NADH must be recycled to NAD+ by either:
1. Aerobic respiration • Oxygen is available as the final
electron acceptor
• Produces significantly more ATP
2. Fermentation • Occurs when oxygen is not
available
• Organic molecule is the final electron acceptor
http://getyournotes.blogspot.com/2012/01/cellular-respiration-aerobic-and.html
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Fate of pyruvate
• Depends on oxygen availability
– When oxygen is present,
pyruvate is oxidized to acetyl-
CoA which enters the Krebs
cycle
• Aerobic respiration
– Without oxygen, pyruvate is
reduced in order to oxidize
NADH back to NAD+
• Fermentation
http://getyournotes.blogspot.com/2012/01/cellular-respiration-aerobic-and.html
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Without oxygen
NAD+
O2 NADH
ETC in mitochondria
Acetyl-CoA
Ethanol
NAD+
CO2
NAD+
H2O
Lactate
Pyruvate
Acetaldehyde NADH
NADH
With oxygen
Krebs
Cycle
– Without oxygen, pyruvate is reduced by
lactate or alcohol fermentation
• This oxidizes NADH back to NAD+
• This is important
because NAD+ must
be recycled so
glycolysis can
continue to operate
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Pyruvate Oxidation
• In the presence of oxygen, pyruvate is
oxidized
– Occurs in the mitochondria in eukaryotes
• multienzyme complex called pyruvate dehydrogenase
catalyzes the reaction
– Occurs at the plasma membrane in prokaryotes
http://schoolworkhelper.net/cellular-respiration-glycolysis-pyruvate-kerbs-etc/
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• For each 3-carbon pyruvate molecule: – 1 CO2
• Decarboxylation by pyruvate dehydrogenase
– 1 NADH
– 1 Acetyl-CoA which consists of 2 carbons from pyruvate attached to coenzyme A
• Acetyl-CoA proceeds to the Krebs cycle
Products of pyruvate oxidation
http://schoolworkhelper.net/cellular-respiration-glycolysis-pyruvate-kerbs-etc/
***Double each of
these products per
glucose molecule
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Glycolysis
Pyruvate Oxidation
NADH
Krebs
Cycle
Electron Transport Chain
Chemiosmosis
Pyruvate Oxidation: The Reaction
NAD+
CO2
CoA
Acetyl Coenzyme A
Pyruvate
Pyru
vate
A
cety
l C
oe
nzym
e A
O
CH 3
C
O–
C O
S CoA
CH3
O C
NADH
Per glucose
molecule =
• 2 CO2
• 2 NADHs
• 2 Acetyl CoA
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Krebs Cycle
• Oxidizes the acetyl group
from pyruvate
• Occurs in the matrix of the
mitochondria
• Biochemical pathway of 9
steps in three segments
1. Acetyl-CoA + oxaloacetate →
citrate
2. Citrate rearrangement and
decarboxylation
3. Regeneration of oxaloacetate
1
2 3
http://drchadedwards.com/244/energy-production-through-the-krebs-cycle/
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30
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
CoA-
(Acetyl-CoA) CoA
4-carbon
molecule
(oxaloacetate) 6-carbon molecule
(citrate)
NAD +
NADH
CO2
5-carbon
molecule
NAD+
NADH
CO2
4-carbon
molecule
ADP + P
Krebs Cycle
FAD
FADH2
4-carbon
molecule
NAD+
NADH
ATP
Glycolysis
Pyruvate Oxidation
Electron Transport Chain
Chemiosmosis
ATP
4-carbon
molecule
Pyruvate from glycolysis is
oxidized Krebs Cycle into an
acetyl group that feeds into the
Krebs cycle. The 2-C acetyl group
combines with 4-C oxaloacetate to
produce the 6-C compound citrate
(thus this is also called the citric
acid cycle). Oxidation reactions
are combined with two
decarboxylations to produce
NADH, CO2, and a new 4-carbon
molecule. Two additional
oxidations generate another
NADH and an FADH2 and
regenerate the original 4-C
oxaloacetate.
NADH
FADH2
Krebs
Cycle
1
2
3
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31
Krebs Cycle
• For each Acetyl-CoA
entering:
– Release 2 molecules of
CO2
– Reduce 3 NAD+ to 3
NADH
– Reduce 1 FAD (electron
carrier) to FADH2
– Produce 1 ATP
– Regenerate oxaloacetate
http://drchadedwards.com/244/energy-production-through-the-krebs-cycle/
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32
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Glycolysis
NADH
F ADH2
Pyruvate Oxidation
ATP
Krebs Cycle: The Reactions
Citrate synthetase
NAD+
NADH
H2O
NAD+
NADH
CO2
Isocitrate dehydrogenase
Fumarase
CoA-SH 1
2
Aconitase 3
4
8
9
7
CoA-SH
NAD+
CO2
5
6
NADH
CoA-SH
GDP + Pi
Acetyl-CoA
═
CH3 — C — S
O CoA —
Krebs
Cycle
Malate
dehydrogenase
-Ketoglutarate
dehydrogenase
Succinyl-CoA
synthetase
GTP
ATP
ADP
Succinate
dehydrogenase
FADH2
8–9. Reactions 8 and 9: Regeneration of
oxaloacetate and the fourth oxidation
7. Reaction 7: The third oxidation
6. Reaction 6: Substrate-level phosphorylation
5. Reaction 5: The second oxidation
4. Reaction 4: The first oxidation
2–3. Reactions 2 and 3: Isomerization
1. Reaction 1: Condensation
Electron T ransport Chain
Chemiosmosis
Oxaloacetate (4C)
CH2
O ═ C
COO—
COO—
—
—
—
Citrate (6C)
HO — C — COO—
COO—
COO—
CH2
CH2
—
—
—
—
Isocitrate (6C)
HC — COO—
COO—
COO—
CH2
HO — CH
—
—
—
—
-Ketoglutarate (5C)
CH2
COO—
COO—
CH2
C — O
—
—
—
—
Succinyl-CoA (4C)
CH2
COO—
S — CoA
CH2
C ═ O
—
—
—
—
Succinate (4C)
COO—
CH2
COO—
CH2
—
—
—
Fumarate (4C)
HC
CH
═
COO—
COO—
—
—
Malate (4C)
HO — CH
COO—
CH2
COO—
—
—
—
FAD
Per glucose
molecule, the
Krebs cycle
produces…
• 4 CO2
• 6 NADHs
• 2 FADH2
• 2 ATP
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33
At this point
• Glucose has been oxidized to:
– 6 CO2 (byproduct of aerobic respiration)
– 4 ATP
– 10 NADH
– 2 FADH2
• Electron transfer has released 53 kcal/mol
of energy by gradual energy extraction
• Energy will be put to use to manufacture
ATP in ETC
These two types of electron carriers proceed to the electron transport chain
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34
Electron Transport Chain (ETC)
• ETC is a series of membrane-bound electron carriers
• Embedded in the inner mitochondrial membrane
Mitochondrial matrix
NADH + H+ H2O
H+ H+
2H+ + 1 / 2 O2
2
NADH dehydrogenase bc1 complex
Cytochrome
oxidase complex
Inner
mitochondrial
membrane
Intermembrane space
a. The electron transport chain
NAD+
Q
C
e–
FADH2
H+
e– 2 2 e– 2 2
FAD
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35
Electron Transport Chain (ETC)
• Electrons from NADH and FADH2 are transferred to complexes of the ETC
• Each complex…
– A proton pump creating proton gradient
– Transfers electrons to next carrier
Mitochondrial matrix
NADH + H+ H2O
H+ H+
2H+ + 1 / 2 O2
2
NADH dehydrogenase bc1 complex
Cytochrome
oxidase complex
Inner
mitochondrial
membrane
Intermembrane space
a. The electron transport chain
NAD+
Q
C
e–
FADH2
H+
e– 2 2 e– 2 2
FAD
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36
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Glycolysi s
Pyruvate Oxidatio n
Krebs
Cycle ATP
Electron Transport Chain
Chemiosmosis
ADP + Pi
ATP
synthase
b. Chemiosmosis
H+
H+ H+ ATP
Mitochondrial matrix
NADH + H+ H2O
H+ H+
2H+ + 1 / 2 O2
2
NADH dehydrogenase bc1 complex
Cytochrome
oxidase complex
Inner
mitochondrial
membrane
Intermembrane space
a. The electron transport chain
NAD+
Q
C
e–
FADH2
H+
e– 2 2 e– 2 2
FAD
Note that O2 is the final electron
acceptor (the reason we require
O2), combining with protons to
form H2O as a byproduct of
aerobic respiration.
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Chemiosmosis
• Accumulation of protons (H+) in intermembrane
space drives protons into the matrix via diffusion
• Membrane relatively impermeable to ions
• Most H+ can only reenter matrix via ATP synthase
– Uses energy of gradient to make ATP from ADP + Pi
– Proton Motive Force
ADP + Pi
ATP
synthase
b. Chemiosmosis
H+
H+ H+ ATP
Mitochondrial matrix
NADH + H+ H2O
H+ H+
2H+ + 1 / 2 O2
2
NADH dehydrogenase bc1 complex
Cytochrome
oxidase complex
Inner
mitochondrial
membrane
Intermembrane space
a. The electron transport chain
NAD+
Q
C
e–
FADH2
H+
e– 2 2 e– 2 2
FAD
H+ H+
H+ H+ H+
H+
H+
H+
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38
ADP + Pi
Catalytic head
Stalk
Rotor
H+
H+
Mitochondrial
matrix
Intermembrane
space
H+ H+
H+
H+ H+
ATP
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39
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
H2O
CO2
CO2
H+
H+
2H+
+ 1 / 2 O2
H+
e–
H+
32 ATP
Krebs
Cycle
2 ATP
NADH
NADH
FADH2
NADH
Pyruvate
Oxidation
Acetyl-CoA
e–
Q
C
e–
Glycolysis
Glucose
Pyruvate
Note the location of each
component of cellular
respiration…glycolysis,
pyruvate oxidation, Krebs
cycle and ETC
Note where the electron
carriers transfer electrons
from…to the ETC
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40
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operating systems, some animations
will not appear until the presentation is
viewed in Presentation Mode (Slide
Show view). You may see blank slides
in the “Normal” or “Slide Sorter” views.
All animations will appear after viewing
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41
Energy Yield of Respiration
• Theoretical energy yield (these values vary from book to book)
– 38 ATP per glucose for bacteria
– 36 ATP per glucose for eukaryotes
• Actual energy yield
– 30 ATP per glucose for eukaryotes
– Reduced yield is due to… • “Leaky” inner membrane
• Use of the proton gradient for purposes other than ATP synthesis
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42
Chemiosmosis
Chemiosmosis
2 5
2 3
6 15
2
2
2 5 NADH
NADH
NADH
Total net ATP yield = 32
(30 in eukaryotes)
ATP
ATP
ATP
ATP
ATP
ATP
Krebs
Cycle
Pyruvate oxidation
FADH2
Glycolysis 2
Glucose
Pyruvate
ATP
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
2.5 ATPs
per NADH
2.5 ATPs
per NADH
1.5 ATPs
per FADH2
??
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43
Regulation of Respiration
• Examples of negative
feedback inhibition
• Two key control points
1. In glycolysis
• Phosphofructokinase is
allosterically inhibited by
ATP and/or citrate
Glucose
Acetyl-CoA
Fructose 6-phosphate
Fructose 1,6-bisphosphate
Pyruvate
Pyruvate Oxidation
Krebs
Cycle
Electron Transport Chain
and
Chemiosmosis
Citrate
ATP
NADH
Inhibits
Inhibits Inhibits
Phosphofructokinase
Pyruvate dehydrogenase
Glycolysis
ADP
Activates
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44
Regulation of Respiration
• Two key control points
2. In pyruvate oxidation
• Pyruvate dehydrogenase
inhibited by high levels of
NADH
• Citrate synthetase
inhibited by high
levels of ATP
Glucose
Acetyl-CoA
Fructose 6-phosphate
Fructose 1,6-bisphosphate
Pyruvate
Pyruvate Oxidation
Krebs
Cycle
Electron Transport Chain
and
Chemiosmosis
Citrate
ATP
NADH
Inhibits
Inhibits Inhibits
Phosphofructokinase
Pyruvate dehydrogenase
Glycolysis
ADP
Activates
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Glucose
Acetyl-CoA
Fructose 6-phosphate
Fructose 1,6-bisphosphate
Pyruvate
Pyruvate Oxidation
Krebs
Cycle
Electron Transport Chain
and
Chemiosmosis
Citrate
ATP
NADH
Inhibits
Inhibits Inhibits
Phosphofructokinase
Pyruvate dehydrogenase
Glycolysis
ADP
Activates
45
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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46
Oxidation Without O2
1. Anaerobic respiration
– Use of inorganic molecules (other than O2) as
final electron acceptor
– Many prokaryotes use sulfur, nitrate, carbon
dioxide or even inorganic metals
2. Fermentation
– Use of organic molecules as final electron
acceptor
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47
Anaerobic respiration
• Methanogens
– CO2 is reduced to CH4 (methane)
– Found in diverse organisms including cows
• Sulfur bacteria
– Inorganic sulphate (SO4) is reduced to
hydrogen sulfide (H2S)
– Early sulfate reducers set the stage for
evolution of photosynthesis
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48
a: © Wolfgang Baumeister/Photo Researchers, Inc.; b: NPS Photo
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
b. a. 0.625 µm
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49
Fermentation
• Reduces organic molecules
in order to regenerate NAD+
to supply glycolysis allowing
it to continue, even in
absence of O2
1. Ethanol fermentation
occurs in yeast
• CO2, ethanol, and NAD+
are produced
CO2
2 Acetaldehyde
2 AD P
2 Lactate
Alcohol Fermentation in Yeast
2 ADP
Lactic Acid Fermentation in Muscle Cells
2 NAD+
2 NAD+
2 NADH
2 NADH
2 ATP
2 ATP
C O
C O
O–
CH3
C O
H
CH3
C O
C O
CH3
O–
CH3
H C OH
C O
O–
H
2 Ethanol
H C OH
CH3
2 Pyruvate
2 Pyruvate
Glucose
Glucose
G
L
Y
C
O
L
Y
S
I
S
G
L
Y
C
O
L
Y
S
I
S
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50
Fermentation
2. Lactic acid
fermentation
• Electrons are transferred
from NADH to pyruvate to
produce lactic acid
• Occurs in animal cells
(especially muscles, such
as during sprinting)
CO2
2 Acetaldehyde
2 AD P
2 Lactate
Alcohol Fermentation in Yeast
2 ADP
Lactic Acid Fermentation in Muscle Cells
2 NAD+
2 NAD+
2 NADH
2 NADH
2 ATP
2 ATP
C O
C O
O–
CH3
C O
H
CH3
C O
C O
CH3
O–
CH3
H C OH
C O
O–
H
2 Ethanol
H C OH
CH3
2 Pyruvate
2 Pyruvate
Glucose
Glucose
G
L
Y
C
O
L
Y
S
I
S
G
L
Y
C
O
L
Y
S
I
S
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51
CO2
2 Acetaldehyde
2 AD P
2 Lactate
Alcohol Fermentation in Yeast
2 ADP
Lactic Acid Fermentation in Muscle Cells
2 NAD+
2 NAD+
2 NADH
2 NADH
2 ATP
2 ATP
C O
C O
O–
CH3
C O
H
CH3
C O
C O
CH3
O–
CH3
H C OH
C O
O–
H
2 Ethanol
H C OH
CH3
2 Pyruvate
2 Pyruvate
Glucose
Glucose
G
L
Y
C
O
L
Y
S
I
S
G
L
Y
C
O
L
Y
S
I
S
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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52
Anabolic and Catabolism Pathways
• Metabolic pathways are
linked to reversible
pathways of cellular
respiration
– Large molecules broken
down and rearranged –
catabolic pathways
– Most larger molecules
needed by the cell are
produced – anabolic
pathways
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53
Example of Catabolism of Protein
• Amino acids undergo deamination to remove the
amino group (-NH2)
• Remainder of the amino acid is converted to a
molecule that enters glycolysis or the Krebs cycle
– Alanine is converted to pyruvate
– Aspartate is converted to oxaloacetate
C
HO O
HO O
C
C
HO O
O
C
C O
C H H
C H H C H H
C H H
C H2N H NH3
HO
Urea
Glutamate α-Ketoglutarate
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54
C
HO O
HO O
C
C
HO O
O
C
C O
C H H
C H H C H H
C H H
C H2N H
NH3
HO
Urea
Glutamate α-Ketoglutarate
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
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55
Catabolism of Fat
• Fats are broken down to fatty
acids and glycerol
– Fatty acids are converted to 2-C
acetyl groups by b-oxidation
– Oxygen-dependent process
• The respiration of a 6-carbon
fatty acid yields 20% more
energy than 6-carbon glucose
• Runs in reverse to produce
fats
CoA
Fatty acid
O O
— C — C — C —
═
H
H
—
═
—
ATP
NADH
H2O
Krebs
Cycle
PPi AMP +
FADH2
Fatty acid
2C shorter
CoA
CoA
Fatty acid
O H
H
— C — C — C —
—
—
H
H
—
═
—
Fatty acid
OH
O H
H
— C — C — C
—
—
H
H
—
—
CoA
FAD
Fatty acid
O H
— C ═ C — C —
—
H —
═
CoA
Fatty acid
O HO
H
— C — C — C —
—
—
H
H
—
═
—
CoA
NAD+
Acetyl-CoA
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Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
CoA
Fatty acid
O O
— C — C — C —
═
H
H
—
═
—
ATP
NADH
H2O
Krebs
Cycle
PPi AMP +
FADH2
Fatty acid
2C shorter
CoA
CoA
Fatty acid
O H
H
— C — C — C —
—
—
H
H
—
═
—
Fatty acid
OH
O H
H
— C — C — C
—
—
H
H
—
—
CoA
FAD
Fatty acid
O H
— C ═ C — C —
—
H —
═
CoA
Fatty acid
O HO
H
— C — C — C —
—
—
H
H
—
═
—
CoA
NAD+
Acetyl-CoA
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Cell building blocks
Deamination b-oxidation Glycolysis
Oxidative respiration
Ultimate metabolic products
Acetyl-CoA
Pyruvate
Macromolecule
degradation
Krebs
Cycle
Nucleic acids Polysaccharides
Nucleotides Amino acids Fatty acids Sugars
Proteins Lipids and fats
NH3 H2O CO2
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Reaction pathways
are reversible to
make & breakdown
most molecules
needed by cells
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Evolution of Metabolism
• Hypothetical timeline
1. Ability to store chemical energy in ATP
2. Evolution of glycolysis • Pathway found in all living organisms
3. Anaerobic photosynthesis (using H2S)
4. Use of H2O in photosynthesis (not H2S) • Begins permanent change in Earth’s
atmosphere about 2.4 Bya
5. Evolution of nitrogen fixation
6. Aerobic respiration evolved most recently