biology 201 chapter 7
TRANSCRIPT
Chapter 07
Lecture and Animation Outline
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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
3
Cellular respiration
• Cellular respiration is a series of reactions• Oxidized – loss of electrons• Reduced – gain of electron• Dehydrogenation – lost electrons are
accompanied by protons– A hydrogen atom is lost (1 electron, 1 proton)
4
Redox• During redox reactions, electrons carry
energy from one molecule to another• Nicotinamide adenosine dinucleotide
(NAD+)
– An electron carrier– NAD+ accepts 2 electrons and 1 proton to
become NADH– Reaction is reversible
5
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Product
Enzyme
NAD+
NAD+ NAD NAD
2e–
H+
+H+
Energy-richmolecule
NAD+
1. Enzymes that use NAD+
as a cofactor for oxidationreactions bind NAD+ and the substrate.
2. In an oxidation–reductionreaction, 2 electrons anda proton are transferredto NAD+, forming NADH.A second proton isdonated to the solution.
3. NADH diffuses awayand can then donateelectrons to othermolecules.
Reduction
Oxidation
HH
HH
HH
H H
• 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
• Transferred to a final electron acceptor
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7
• 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
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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.
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2e–
Electrons from food
High energy
Low energy
2H+ 1/2O2
Energy releasedfor 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
10
11
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H H
O
NH2 + 2H
CH2O
O
O
H
H
NH2
H
H
N
N
N
CH2O
O
O
H
H
NH2
O–
H
H
NN
N
H H O
N
N
H H
H
C C
O P
O PO–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 OHOH
OHOH
NH2 + H+
CH2
O–
12
ATP• Cells use ATP to drive endergonic
reactions– ΔG (free energy) = –7.3 kcal/mol
• 2 mechanisms for synthesis1. Substrate-level phosphorylation
• Transfer phosphate group directly to ADP• During glycolysis
2. Oxidative phosphorylation• ATP synthase uses energy from a proton gradient
13
PEP
– ADP
Enzyme Enzyme
– ATPAdenosine
Pyruvate
P
PP
P
P
Adenosine
P
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14
Oxidation of Glucose
The complete oxidation of glucose proceeds in stages:
1. Glycolysis2. Pyruvate oxidation3. Krebs cycle4. Electron transport chain & chemiosmosis
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Outermitochondrial
membrane
Intermembranespace
Mitochondrialmatrix
FAD O2
Innermitochondrial
membrane
ElectronTransport Chain
ChemiosmosisATP Synthase
NAD+
Glycolysis
Pyruvate
Glucose
PyruvateOxidation
Acetyl-CoA
KrebsCycle
CO2
ATPH2O
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• Net production of 2 ATP molecules by
substrate-level phosphorylation• 2 NADH produced by the reduction of
NAD+
17
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Glycolysis
NADH
Pyruvate Oxidation
ATP
Electron Transport ChainChemiosmosis
KrebsCycle
6-carbon sugar diphosphate
NAD+ NAD+
Prim
ing
Rea
ctio
nsC
leav
age
Oxi
datio
n an
d A
TP F
orm
atio
n
NADH NADH
P P
P P
ATP ATP
ADP ADP
3-carbon sugarphosphate
3-carbon sugarphosphate
PiPi
ADP ADP
ATP ATP
ATP
ADP ADP
ATP
3-carbonpyruvate
3-carbonpyruvate
6-carbon glucose(Starting material)
Glycolysis beginswith the addition ofenergy. Two high-energy phosphates(P) from twomolecules of ATPare added to the6-carbon moleculeglucose, producinga 6-carbonmolecule with twophosphates.
Then, the 6-carbonmolecule with twophosphates is split in two, forming two3-carbon sugarphosphates.
An additionalInorganic phosphate ( Pi ) is incorporated into each 3-carbon sugar phosphate. Anoxidation reactionconverts the twosugar phosphatesinto intermediatesthat can transfer aphosphate to ADP to form ATP. Theoxidation reactionsalso yield NADHgiving a net energyyield of 2 ATP and 2NADH.
18
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NADH
NAD+
NADH
PiNAD+
Glucose
Hexokinase
Phosphofructokinase
Glucose 6-phosphate
Fructose 6-phosphate
Fructose 1,6-bisphosphate
IsomeraseAldolase
Pyruvate Pyruvate
Enolase
Pyruvate kinase
ADP
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Glu
cose
Gly
cera
ldeh
yde
3-ph
osph
ate
Pyru
vate
Glycolysis: The ReactionsGlycolysis
NADH
Pyruvate Oxidation
H2O
ATP
ADP
Electron Transport ChainChemiosmosis
KrebsCycle
ATP
ATP
Phosphoglucoseisomerase
Glyceraldehyde 3-phosphate (G3P)
Dihydroxyacetonephosphate
1. Phosphorylation ofglucose by ATP.
2–3. Rearrangement,followed by a secondATP phosphorylation.
4–5. The 6-carbon moleculeis split into two 3-carbonmolecules—one G3P,another that is convertedinto G3P in anotherreaction.
6. Oxidation followed byphosphorylation producestwo NADH molecules andtwo molecules of BPG,each with onehigh-energy phosphatebond.
7. Removal of high-energyphosphate by two ADPmolecules produces twoATP molecules and leavestwo 3PG molecules.
8–9. Removal of water yieldstwo PEP molecules, eachwith a high-energyphosphate bond.
10. Removal of high-energyphosphate by two ADPmolecules produces twoATP molecules and two pyruvate molecules.
1,3-Bisphosphoglycerate (BPG) 1,3-Bisphosphoglycerate
(BPG)
Glyceraldehyde3-phosphate
dehydrogenase
Pi
ADP
Phosphoglyceratekinase
ADP
ATP
3-Phosphoglycerate(3PG)
3-Phosphoglycerate(3PG)
2-Phosphoglycerate(2PG)
2-Phosphoglycerate(2PG)
H2O
ATP
Phosphoenolpyruvate(PEP)
Phosphoenolpyruvate(PEP)
ADP ADP
ATP ATP
Phos
phoe
nol-
pyru
vate
3-Ph
osph
o-gl
ycer
ate
1,3-
Bis
phos
pho-
glyc
erat
eG
luco
se6-
phos
phat
eFr
ucto
se6-
phos
phat
eFr
ucto
se1,
6-bi
spho
spha
teD
ihyd
roxy
acet
one
Phos
phat
e2-
Phos
pho-
glyc
erat
e
CH2OHO
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 CH2P
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
19
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20
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 significant amount of ATP
2. Fermentation– Occurs when oxygen is not available– Organic molecule is the final electron acceptor
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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
22
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Without oxygen
NAD+
O2 NADH
ETC in mitochondria
Acetyl-CoA
Ethanol
NAD+
CO2
NAD+
H2O
Lactate
Pyruvate
AcetaldehydeNADH
NADH
With oxygen
KrebsCycle
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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
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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
25
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Glycolysis
Pyruvate Oxidation
NADH
KrebsCycle
Electron Transport ChainChemiosmosis
Pyruvate Oxidation: The Reaction
NAD+
CO2
CoA
Acetyl Coenzyme A
Pyruvate
Pyru
vate
Ace
tyl C
oenz
yme
A
O
CH 3
C
O–
C O
S CoA
CH3
OC
NADH
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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 → citrate2. Citrate rearrangement and decarboxylation3. Regeneration of oxaloacetate
27
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CoA-(Acetyl-CoA)
CoA
4-carbonmolecule
(oxaloacetate) 6-carbon molecule(citrate)
NAD +
NADH
CO2
5-carbonmolecule
NAD+
NADH
CO2
4-carbonmolecule
ADP + P
Krebs Cycle
FAD
FADH2
4-carbonmolecule
NAD+
NADH
ATP
Glycolysis
Pyruvate Oxidation
Electron Transport ChainChemiosmosis
ATP
4-carbonmolecule
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
KrebsCycle
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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
29
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Glycolysis
NADH
FADH2
Pyruvate Oxidation
ATP
Krebs Cycle: The Reactions
Citratesynthetase
NAD+
NADH
H2O
NAD+
NADH
CO2
Isocitratedehydrogenase
Fumarase
CoA-SH1
2
Aconitase3
4
8
9
7
CoA-SH
NAD+
CO2
5
6
NADH
CoA-SH
GDP + Pi
Acetyl-CoA
═
CH3— C— S
O CoA—
KrebsCycle
Malatedehydrogenase
-Ketoglutaratedehydrogenase
Succinyl-CoAsynthetase
GTP
ATP
ADP
Succinatedehydrogenase
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 ChainChemiosmosis
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
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At this point
• Glucose has been oxidized to:– 6 CO2
– 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
These electron carriers proceedto the electron transport chain
31
Electron Transport Chain (ETC)
• ETC is a series of membrane-bound electron carriers
• Embedded in the inner mitochondrial membrane
• 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
32
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Mitochondrial matrix
NADH + H+ADP + PiH2O
H+ H+
2H+ + 1/2O2
Glycolysis
Pyruvate Oxidation
2
KrebsCycle ATP
Electron Transport ChainChemiosmosis
NADH dehydrogenase bc1 complexCytochrome
oxidase complex
Innermitochondrial membrane
Intermembrane space
a. The electron transport chain
ATPsynthase
b. Chemiosmosis
NAD+
QC
e–
FADH2
H+H+
H+H+
e–22 e–22
ATP
FAD
33
Chemiosmosis
• Accumulation of protons in the intermembrane space drives protons into the matrix via diffusion
• Membrane relatively impermeable to ions• Most protons can only reenter matrix
through ATP synthase– Uses energy of gradient to make ATP from
ADP + Pi
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ADP + Pi
Catalytic head
Stalk
Rotor
H+
H+
Mitochondrialmatrix
Intermembranespace
H+ H+
H+
H+H+
ATP
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35
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H2O
CO2
CO2
H+
H+
2H+
+1/2O2
H+
e–
H+
32 ATPKrebsCycle
2 ATP
NADH
NADH
FADH2
NADH
PyruvateOxidationAcetyl-CoA
e–
QC
e–
Glycolysis
Glucose
Pyruvate
36
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37
Energy Yield of Respiration
• Theoretical energy yield– 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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Chemiosmosis
Chemiosmosis
2 5
2 3
6 15
2
2
2 5NADH
NADH
NADH
Total net ATP yield = 32(30 in eukaryotes)
ATP
ATP
ATP
ATP
ATP
ATP
KrebsCycle
Pyruvate oxidation
FADH2
Glycolysis2
Glucose
Pyruvate
ATP
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39
Regulation of Respiration
• Example of feedback inhibition• 2 key control points
1. In glycolysis• Phosphofructokinase is allosterically inhibited by
ATP and/or citrate
2. In pyruvate oxidation• Pyruvate dehydrogenase inhibited by high levels of
NADH• Citrate synthetase inhibited by high levels of ATP
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Glucose
Acetyl-CoA
Fructose 6-phosphate
Fructose 1,6-bisphosphate
Pyruvate
Pyruvate Oxidation
KrebsCycle
Electron Transport Chainand
Chemiosmosis
Citrate
ATP
NADH
Inhibits
InhibitsInhibits
Phosphofructokinase
Pyruvate dehydrogenase
GlycolysisCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
ADP
Activates
41
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
42
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
43
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44
Fermentation
• Reduces organic molecules in order to regenerate NAD+
1. Ethanol fermentation occurs in yeast– CO2, ethanol, and NAD+ are produced
2. Lactic acid fermentation– Occurs in animal cells (especially muscles)– Electrons are transferred from NADH to
pyruvate to produce lactic acid
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CO2
2 Acetaldehyde
2 ADP
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
GLYCOLYSIS
GLYCOLYSIS
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46
Catabolism of Protein• Amino acids undergo deamination to
remove the amino group• 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
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C
HO O
HO O
C
C
HO O
O
C
C O
CH H
CH HCH H
CH H
CH2N HNH3
HO
Urea
Glutamate α-Ketoglutarate
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48
Catabolism of Fat
• Fats are broken down to fatty acids and glycerol– Fatty acids are converted to acetyl groups by
-oxidation – Oxygen-dependent process
• The respiration of a 6-carbon fatty acid yields 20% more energy than 6-carbon glucose.
49
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CoA
Fatty acid
OO
—C —C—C—
═ H
H
— ═—
ATP
NADH
H2O
KrebsCycle
PPiAMP +
FADH2
Fatty acid2C shorter
CoA
CoA
Fatty acid
OH
H
—C — C—C—
——
H
H
— ═—
Fatty acidOH
OH
H
—C —C— C═
—
——
H
H
——
CoA
FAD
Fatty acid
OH
—C ═ C —C—
— H— ═
CoA
Fatty acid
OHO
H
—C —C—C—
——
H
H— ═
— CoA
NAD+
Acetyl-CoA
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Cell building blocks
Deamination -oxidationGlycolysis
Oxidative respiration
Ultimate metabolic products
Acetyl-CoA
Pyruvate
Macromoleculedegradation
KrebsCycle
Nucleic acids Polysaccharides
Nucleotides Amino acids Fatty acidsSugars
Proteins Lipids and fats
NH3 H2O CO2
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51
Evolution of Metabolism
• Hypothetical timeline1. Ability to store chemical energy in ATP2. 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 atmosphere5. Evolution of nitrogen fixation6. Aerobic respiration evolved most recently