Microbial Metabolism: The Chemical Crossroads of Life Chapter 8 Copyright © The McGraw-Hill Companies, Inc) Permission required for reproduction or display.
Microbial Metabolism: The Chemical Crossroads
of LifeChapter 8
Copyright © The McGraw-Hill Companies, Inc) Permission required for reproduction or display.
Metabolism
• Catabolism
• Anabolism
• Energy
• ATP
• Gradients
Glucose CATABOLISMANABOLISM
ANABOLISM
ANABOLISMR
elat
ive
com
ple
xity
of
mo
lecu
les
+
Bacterialcell
Macromolecules
Nutrients fromoutside or frominternal pathways
PyruvateAcetyl CoAGlyceraldehyde-3-P
Amino acidsSugarsNucleotidesFatty acids
ProteinsPeptidoglycanRNA + DNAComplex lipids
GlycolysisKrebs cycleRespiratory chainFermentation
Yields energy
Buildingblocks
Precursormolecules
ATP
NADH
Uses energy Uses energy Uses energy;some assembly reactions
occur spontaneously.
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Enzymes
• Biological catalysts critical for life
• Nearly always proteins
• Active site
• Substrate(s)
• Cofactors
E
Products
Substrate (S)
Enzyme (E) Doesnot fit
ES complex
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Reaction Energetics
• Activation energy
• Lowered by enzyme
• Exergonic releases energy – catabolism
• Endergonic uses energy – anabolism E
ne
rgy
Sta
te o
f R
ea
cti
on
Energy of activation in theabsence of enzymeEnergy of activation in thepresence of enzyme
Progress of Reaction
Final state
Products
Initialstate
Reactant
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Enzyme Pathways
• Linking products to substrates
• Sequential modifications
• Results in energy – catabolism
• Results in biosynthesis - anabolism
A
B
C
D
E
U
V
W
X
Z
Y
O2
O
O1
M
N
P
Q
R
M
A
B
C
N
X
Y
Z
Multienzyme Systems
Linear Cyclic
Example:Glycolysis
Example:Krebs cycle
Tinput
S product
Example:Amino acidsynthesis
Convergent
Branched
Divergent
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Strategy of Metabolism
• Use catabolism to
• Release energyCapture electrons
• Liberate building blocks
• Drive anabolism by
• Spending energy
• Using electrons
• Using building blocks
O
HO
H
CH2OH6
H
OH H
H
OH
C
CO2
C
C
C
C
C
5
4
3 2
13
H OH
En
erg
y L
evel
Of
Ch
emic
al C
om
po
un
d
O
1
2
The energy in electrons andhydrogens is captured andtransferred to ATP. ATP is spentto drive the thousands of cellfunctions.
ATPused to perform
cellular work
Hydrogen ionswith electrons
Hydrogen ionswith electrons
ATP
Progress of Energy Extraction over Time
These reactions lower theavailable energy in each successivereaction, but they effectively routethat energy into useful cell activities.
Low
High
Hydrogen ionswith electrons
Glucose
2H+ + 2e– O2
H2O
O
1–2
+
End products
Final electronacceptor
Glucoseis oxidizedas it passesmetabolic pathways,resulting in the removalof hydrogens and theiraccompanying electrons.During part of these pathways, theglucose carbon skeleton is alsodismantled, giving rise to the end productCO2.
―― ――
Oxidation of glucose by means
of enzyme-catalyzed pathways
4In aerobic metabolism,the electrons and hydrogenions generated by therespiratory pathwayscombine with oxygen toproduce another rendproduct, water.
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Key Intermediates (building blocks)
• Glucose 6-Phosphate 6-Carbon Glycolysis
• Fructose 6-Phosphate 6-Carbon Glycolysis
• Triose Phosphate 3-Carbon Glycolysis
• 3-Phosphoglycerate 3-Carbon Glycolysis
• Phosphoenolpyruvate 3-Carbon Glycolysis
• Pyruvate 3-Carbon Glycolysis
• Acetyl CoA 2-Carbon Krebs cycle
-Ketoglutyrate 5-Carbon Krebs cycle
• Succinyl CoA 4-Carbon Krebs cycle
• Oxaloacetate 4-Carbon Krebs cycle
• Ribose 5-Phosphate 5-Carbon Pentose phosphate
• Erythrose 4-Phosphate 4-Carbon Pentose phosphate
Concept Check
What type of chemical reaction is illustrated here?
A. Exergonic
B. Endergonic
C. Spontaneous
D. Anabolic
En
erg
y S
tate
of
Rea
ctio
n
Energy of activation in theabsence of enzymeEnergy of activation in thepresence of enzyme
Progress of Reaction
Final state
Products
Initialstate
Reactant
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ATP
• Adenosine triphosphate
• Components
• Base (adenine)
• Sugar (ribose)
• Phosphate (3)
• Energy stored in the phosphate bonds
2H
2e:
N
NH2
O
H
C
C C
CC
C
P
P
N
H
C
C C
CC
C
O
P
P
H H+
Oxidizednic otinamide Reducednic otinamide
NAD
From substrate
Adenine
Ribose
NH2
NADH + H+
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Substrate Level Phosphorylation
• ATP can be used to drive reactions
Glucose + ATP Glucose-6-phosphate + ADP
• Some compounds can be used to make ATP
Phosphoenolpyruvate + ADP pyruvate + ATP
• This is called substrate level phosphorylation
Oxidation/Reduction
• Oxidation is losing electrons
• Reduction is gaining electrons
• Oxidation is always linked to reduction
2 8 1 2 82 8 7 2 8 8
1 2
Reducedanion
ClNaClNa
Reducing agentgives up electrons.
Oxidizing agentaccepts electrons.
Oxidizedcation
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NAD
• Nicotinamide adenine dinucleotide
• Electron acceptor
• Limited amount in the cell
• Must be re-oxidized from the reduced form
2H
2e:
N
NH2
O
H
C
C C
CC
C
P
P
N
H
C
C C
CC
C
O
P
P
H H+
Oxidizednic otinamide Reducednic otinamide
NAD
From substrate
Adenine
Ribose
NH2
NADH + H+
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Glycolysis (Stage 1)
Glucose Glucose 6-Phosphate
A A
Fructose 6-Phosphate
A A
Fructose 1,6-Biphosphate
Energy is spent in the front end to get more later.
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Glycolysis (Stage 2)
Fructose 1,6-Biphosphate PGAL &
DHAP
+
1,3 Bisphospho-glycerate
2X
2 NAD+
2 NADH + 2H+2
Splitting into two molecules doubles the reactants.
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Glycolysis (Stage 3)
1,3 Bisphospho-glycerate
2X
2X
2X
AA2X
3 PGA
2X
2 PGA
Break-even point using substrate-level phosphorylation.
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2X
Phosphoenolpyruvate
Glycolysis (Stage 4)
2 PGA
2X
2XAA
2X
2X
Pyruvate
The payoff - a net yield of ATP by substrate level phosphorylation
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Concept Check
How many net ATP are formed in glycolysis?
A. One
B. Two
C. Three
D. Four
Glycolysis Summary
• One glucose is used
• Partial oxidation of the sugar
• Two NADH are reduced
• 2 ATP are consumed
• 4 ATP total are made
• Net of 2 ATP produced
• 2 pyruvates are end products
The Kreb’s Cycle• Complete oxidation to CO2
C
CH2
HC
HO CH2
CO2
C
C
H+
COO–
CH2
CH2
C O
COO–
COO–
CH2
HO
NAD+
CO2
C H2
C
C
C
O
O S
O
C S
C H3
C
C H2
C
C H2
Acetyl CoA
Isocitric acid
8
8
1
2
3
4
5
5
6
7
7
6
3
2
PO4–3
C
O
C H3
O
C
CoA
CH2
C
C H
HC
C
C
C H
C
C
C
C H2
OC
O–
O–
+
H++
H++
H++
C
C
CH2
HC
CO2
ATPADP
Succinyl CoA
CoA
CO2
NAD H
NAD+
An additional NADHis formed when malicacid is converted tooxaloacetic acid, whichis the final product toenter the cycle again, byreacting with acetyl CoA.
Fumaric acidreacts withwater to formmalic acid.
Succinic acid loses 2Hand 2e–, yieldingfumaric acid andgenerating FADH2.
Succinyl CoA isconverted to succinicacid and regeneratesCoA. This releasesenergy that iscaptured in ATP.
a-ketoglutaric acidloses the secondCO2 and generatesanother NADH+
plus 4C succinyl CoA.
Isocitric acid isconverted to 5Ca-ketoglutaricacid, whichyields NADHand CO2.
Citrate changes thearrangement of atomsto form isocitric acid.
The 2 Cacetyl CoAmolecule combineswith oxaloacetic acid,forming 6C citrate, andreleasing CoA.
a-ketoglutaric acid
NAD H
NAD+
OO–
OO–
Citric acid
CoA
OO–
OO–
OO–
CoA
Pyruvic acid
From glycolysis
NAD H
Oxaloacetic acid
OO–
OO–
H2O
Malic acid
OO–
HO
OO–
NAD+
NAD H
Krebs Cycle
OO–
OO–
FADH2
FAD
OO–
OO–
Fumaric acid
Succinic acid
AEROBIC RESPIRATION ANAEROBIC RESPIRATION FERMENTATION
Glycolysis Glycolysis Glycolysis
Glucose Glucose Glucose
ATPNADH
ATP
NADHATP
NADH2pyruvate(3C)
(6C)
2pyruvate 2pyruvate
(6C)
(3C) (3C)
(6C)
CO2CO2
Acety lCoA Acetyl CoA Fermentation
FADH2
NADH
ATP
Krebs CO2
Electrons
Electron transport
ATP produced = 38
O2 is final electronacceptor.
FADH2
NADHKrebs
ATP
CO2
Electrons
Electron transport
ATP produced = 2 to 36 ATP produced =2
Lactic acidAcetaldehyde
Ethanol
Or other alcohols,acids, gases
An organic molecule is finalelectron accept or (pyruvate,acetaldehyde etc.).
Non oxygen electron acceptors(examples: SO4
2–, NO3–,
CO32– )
1
4
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Kreb’s Cycle Summary
Pyruvate 1
• 3 CO2
• 4 NADH
• 1 FADH2
• 1 ATP
Pyruvate 2
• 3 CO2
• 4 NADH
• 1 FADH2
• 1 ATP• Each glucose has now been completely oxidized
to carbon dioxide• Electrons are temporarily on carrier molecules• 4 ATP total made by substrate level
phosphorylation
Regenerating NAD+
• From one glucose…
• Glycolysis = 2 NADH
• Kreb’s cycle = 8 NADH & 2 FADH2
• There is a limited amount of NAD in the cell, so it must be regenerated for reuse later.
Concept Check
What is the process of making ATP from the degradation of phosphoenolpyruate called?
ADP + Pi + PEP Pyruvate + ATP
A. Oxidative phosphorylation
B. Oxidative decarboxylation
C. Photophosphorylation
D. Substrate level phosphorylation
Fermentation
• Performed by anaerobic microorganisms
• Primary purpose: Regenerate NAD for reuse
• The electron acceptor is an organic molecule
• Secondary purpose: Generate additional energy
• Energy yields are very small
• As a consequence the growth rates are slower
Fermentation
• NADH oxidized
• Organic molecule reduced
• Many possible end products
• Lactic acid
• Ethanol
• Vinegar
• Acetone
C C
OO
C
H
H
H
OHC C
H
H
H
H
H
C C
O
H
H
H
H
CC C
H
H
H
H
O HO
OH
System: Homolactic bacteria;human muscleGlucose
System: Yeasts
Glycolysis
Lactic acidEthyl alcohol
Pyruvic acid
OH
NADH
NAD HNADH
NAD
NAD
CO2
Acetaldehyde
O2 is final electronacceptor.
ATP produced = 38 ATP produced = 2 to 36 ATP produced = 2
Non oxygen electron acceptors (examples: SO4
2–, NO3–, CO3
2– )
An organic molecule is finalelectron accept or (pyruvate,acetaldehyde, etc.).
AEROBIC RESPIRATION
Glycolysis
Glucose
ATP
NADH
2pyruvate (3C)
(6C)
CO2
Acety lCoA
FADH2
NADH
ATP
Krebs CO2
Electrons
Electron transport
ANAEROBIC RESPIRATION
Glycolysis
Glucose
ATP
NADH
2pyruvate (3C)
(6C)
CO2
Acety lCoA
FADH2
NADH
ATP
Krebs CO2
Electrons
Electron transport
FERMENTATION
CO2
Glycolysis
Glucose
ATP
NADH
2pyruvate
Lactic acid
Ethanol
Or other alcohols,acids, gases
Acetaldehyde
(6C)
(3C)
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Redox Potential Energy
• Molecules differ in their affinity for electrons
• Moving from a good donor to a good acceptor is favorable and releases energy
• NADH is a good donor
• Oxygen is the best acceptor
• Want to couple this to do work
Electron Transport System
• NADH oxidized
• Electrons pass through membrane carriers
• Protons pumped out (work is done)
• Electrons accepted by an inorganic molecule
H
H
HH
H
HH
H
H
H
HH
H
HH
H
H
H
H
H
Cell wall
Cytochromes
Cytoplasm
Cell membranewith ETS
ATP
ADP
ATP synthase
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Anaerobic Respiration
• The electron acceptor is not oxygen
• Examples: nitrate, nitrite, and sulfate
• These are mediocre acceptors – not as good as oxygen
• Yields other inorganic molecules upon reduction
• Less favorable reactions pump out fewer protons
Concept Check
Which of these is the best electron acceptor?
A. Oxygen
B. Nitrate
C. Pyruvate
D. NAD
Aerobic Respiration
• The electron acceptor is an oxygen
• This is a very good acceptor
• Yields water upon reduction
• Because so much energy is released, the cell can pumps out about 10 protons
• Occurs in bacterial membrane and mitochondria of eukaryotes
Chemiosmosis
• Proton gradient is potential energy
• Allowing protons back into the cell can be coupled to work
• 3 protons entering drive the synthesis of 1 ATP
• Oxidative phosphorylation
H+
F0
e–
HH
O
O
H+
1 /2 O2
(c) The distribution of electric potential and the concentration gradient of protons across the membrane drive the synthesis of ATP by ATP synthase. The rotation of this enzyme couples diffusion of H+ to the inner compartment with the bonding of ADP and Pi. The final event of electron transport is there action of the electrons with the Hand O2 to form metabolic H2O. This step is catalyzed by cytochrome aa3.
H+
H+
H+
H+
H+
ATPADP + Pi
ATPsynthase
H+
Outercompartment
e–
Cytochromeaa3
H+H+
H+
H+
H+
H+ H+
H+
H+H+
H+
H+
Innercompartment
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Aerobic Respiration Yield
• 1 Glucose 6 CO2
• 2 ATP from glycolysis
• 2 NADH from glycolysis 6 ATP
• 2 ATP from Krebs cycle substrate level
• 8 NADH from Krebs cycle 24 ATP
• 2 FADH2 from Krebs cycle 4 ATP
• Total 36-38 ATP per glucose
Amphibolism
CO2
H2O
Gly
coly
sis
An
abo
lism
Cat
abo
lism
Simpleproducts
Metabolicpathways
Building block
Macromolecule
Cellstructure
Chromosomes EnzymesMembranes
Cell wallStorage
MembranesStorage
LipidsFats
StarchCelluloseProteinsNucleic
acids
Nucleotides Amino acids Carbohydrates Fatty acids
Beta oxidationDeamination
GLUCOSE
Pyruvic acid
Krebscycle
Acetyl coenzyme A
NH3
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Oxygenic Photosynthesis
• Chlorophyll pigments
• Thylakoid membrane
• Capture light energy
• Electron transport
• Photophosphorylation
• Makes NADH and ATP
• Oxygen produced
• Algae, plants, and cyanobacteria
½ O2
2e–
2H+
Pi
Ph
oto
lys
is
Elec
tron
carr
iers
Ca
lvin
Cyc
les
A B
D C
N N
N
Mg
N
H+
H+
H+
H+
H+H+H+
1
2
3
4
5
6
(a) A cell of the motile alga Chlamydomonas,with a single large chloroplast (magnifiedcut away view). The chloroplast containsmembranous compartments called granawhere chlorophyll molecules and thephotosystems for the light reactionsare located.
(b) A chlorophyll molecule,with a central magnesiumatom held by a porphyrin ring.
Flagellum
Nucleus
Cell wall
Chloroplast
Photons
Granum
Stroma
Thylakoid membrane
NADPH
ATP
ADP +
NADP
2e–
P700
Electroncarriers
Photosystem I2e–
P680
Photosystem IIH2OH2O
ATPATPsynthasesynthase
ProtonpumpProtonpump
Interior of granum
(c) The main events of the light reaction shown as an exploded view in one granum.
When light activates photosystem II, it sets up a chain reaction, inwhich electrons are released from chlorophyll.
1
2
3
4
5
6 Both NADPH and ATP are fed into the stroma for the Calvin cycle.
The final electron and H+ acceptor is NADP, which receives these fromphotosystem I.
Pumping of H+ into the interior of the granum produces conditions forATP to be synthesied.
The empty position in photosystem II is replenished photolysis ofH2O.Other products of photolysis are O2 and H+
These electrons are transported along a chain of carriers tophotosystem I.
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Anoxygenic Photosynthesis
• Purple bacteria (similar to photosystem II)
• Make ATP
• Can’t make NADH
• No oxygen produced
• Green bacteria (similar to photosystem I)
• Make ATP
• Also make NADH
• No oxygen produced
Calvin Benson Cycle
• Fix carbon dioxide
• Autotrophs
• Reverse of glycolysis
• 6 CO2 Glucose
P P
PP
PP
P P
P P
PP
P
PH
H
Splitting
ADP
ATP × 2
ADP
ATP
Series of 7 Carbonand 5 Carbonintermediates
Ribulose-1,5-bisphosphate5Carbon
CO2
6 Carbonintermediate
NADPH × 2
NADP
Glyceraldehyde-3phosphate
Glucose
Fructose intermediates
1,3-bisphosphoglyceric acid
Calvin Cycle
3-phosphoglycericacid
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Concept Check
Where does aerobic respiration occur in a yeast?
A. Nucleus
B. Cell membrane
C. Mitochondria
D. Ribosome