MIT Department of Biology
7.014 Introductory Biology, Spring 2005
7.014
7.014
Lecture 17:
17:
Carbon and Energy Metabolism
Metabolism
March 14, 2005
Summary of the options for Life
(the simplified view – see also Freeman Ch 25)
Organism
Carbon Source
Energy Source
Autotrophs
Oxygenic Photosynthesis
pro and euk
CO2
sun
Anoxygenic
Photosynthesis
prokaryotic
CO2
sun
Chemosynthesis
prokaryotic
CO2
Reduced chemical
compounds
Aerobic Respiration
pro or euk
organic C
organic C
Anaerobic Respiration
pro or euk
organic C
organic C
Fermentation
pro or euk
organic C
organic C
Heterotrophs
euk = eukaryotic
1
PHYCOER
YTHRIN
YLL b
CHLOROPH
B- CAROTENE
YLL a
400
WAVELENGTH OF LIGHT (nm)
CHLOROPH
ABSORPTION
YANIN
PHYCOC
UV
700
Figure by MIT OCW.
Figure removed due to copyright considerations.
Please see:
Freeman, Scott. Biological Science. Upper Saddle River, NJ:
Prentice Hall, 2002. ISBN: 0130819239. Fig 25-6.
2
“Dark reactions”
(common to all)
NADPH+
NADP+
CO2
glucose
ATP
ADP + Pi
Photosynthesis
Light
O2
B
e-
+
NADP
H2O A
(Photo)Autotrophs
NADPH
H
+
Plant Photosynthesis
⎯→ ATP
ADP + Pi ⎯
“Dark reactions”
(common to all)
NADPH+
NADP+
CO2
glucose
ATP
ADP + Pi
Photosynthesis
Light
S, SO4
B
-
e
+
NADP
H2S A
(Photo)Autotrophs
NADPH
H
+
Bacterial Photosynthesis
(anaerobic)
⎯→ ATP
ADP + Pi ⎯
3
“Dark reactions”
(common to all)
NADPH+
NADP+
CO2
glucose
ATP
ADP + Pi
Photosynthesis
Light
B
(Photo)Autotrophs
-
e
+
NADP
A
NADPH
H
ATP and NADPH produced in
light reaction used on dark
reaction
+
⎯→ ATP
ADP + Pi ⎯
“Dark reactions”
(common to all)
Photosynthesis
Type
A
B
oxygenic (plant)
H2O
⇒
O2
anyoxygenic
H2S
⇒
S, SO42−
NADPH+
NADP+
CO2
glucose
ATP
ADP + Pi
Net Reaction
Light
B
(Photo)Autotrophs
-
e
+
NADP
A
NET: Light energy used to
convert CO2 to glucose
NADPH
H
+
⎯→ ATP
ADP + Pi ⎯
Type
A
B
oxygenic (plant)
H2O
⇒
O2
anyoxygenic
H2S
⇒
S, SO42−
4
(Chemo) Autotrophs “Dark reactions”
NADPH+
NADP+
CO2
glucose
ATP
ADP + Pi
(common to all)
Chemosynthesis
e−
D
E
F
C
(releases energy)
H+ gradient
ADP + Pi
(requires energy)
e−
(requires energy)
ATP
NADP+
D
C
Type
C
sulfur-oxidizing
H2S
H2S
⇒
⇒
nitrifying
NH3
NO2
⇒
NADPH
D
E
S, SO42−
S, SO42−
O2
NO3−
⇒
⇒
H2O
N2O
O2
⇒
H2O
NO3
−
F
(Chemo) Autotrophs“Dark reactions”
NADPH+
NADP+
CO2
glucose
ATP
ADP + Pi
(common to all)
Chemosynthesis
e−
D
E
F
C
(releases energy)
H+ gradient
ADP + Pi
(requires energy)
e−
(requires energy)
ATP
Type
C
sulfur-oxidizing
H2S
H2S
⇒
⇒
nitrifying
NH3
NO2
⇒
D
NADP+
C
NADPH
D
E
S, SO42−
S, SO42−
O2
NO3−
⇒
⇒
H2O
N2O
O2
⇒
H2O
NO3
−
F
Chemical energy
used to convert
CO2 to glucose
5
Figure removed due to copyright considerations.
Please see:
Freeman, Scott. Biological Science. Upper Saddle River, NJ:
Prentice Hall, 2002. ISBN: 0130819239. Fig 25-5.
glucose
Respiration
+
NAD
ATP
NADH
pyruvate
+
NAD
Krebs’
cycle
Heterotrophs
NADH
CO2
+
NAD
−
e
NADH
A
O2
B
H2O
Aerobic Respiration
+
H gradient
⎯→ ATP
ADP + Pi ⎯
6
glucose
Respiration
Fermentation
+
NAD
ATP
Lactate (3C)
or
Ethanol (2C)
NADH
pyruvate
+
NAD
Krebs’
cycle
Heterotrophs
NADH
Fermentation
CO2
+
NAD
−
e
A
NADH
B
+
H gradient
⎯→ ATP
ADP + Pi ⎯
glucose
Respiration
+
NAD
ATP
NADH
pyruvate
+
NAD
Krebs’
cycle
NADH
Heterotrophs
Anaerobic Respiration
CO2
+
NAD
−
e
NADH
A
NO3 --
B
NO, N2, N2O,NH3
+
H gradient
⎯→ ATP
ADP + Pi ⎯
7
glucose
Respiration
+
NAD
ATP
NADH
pyruvate
+
NAD
Krebs’
cycle
Heterotrophs
Anaerobic Respiration
NADH
CO2
+
NAD
−
e
A
NADH
These are examples: Many things
can serve as electron acceptors
B
+
H gradient
⎯→ ATP
ADP + Pi ⎯
Type
A
aerobic
O2
B
2−
sulfate-reducing
SO4
denitrifying
NO3−
⇒
H2O
⇒
H2S or S
⇒
NO, N2, N2O, NH3
Figure removed due to copyright considerations.
Please see:
Freeman, Scott. Biological Science. Upper Saddle River, NJ:
Prentice Hall, 2002. ISBN: 0130819239. Fig 25-5.
8
Glucose
Oxidized
Compounds
SO4 –
NO 3–
H 2S
SO4
Bacterial photosynthesis
O2
NH4 +
H 2S
Anaerobic respiration
H 2O
Chemosynthesis
“CH2O”
Aerobic respiration
Photosynthesis
Reduced
Compounds
CO2
Oxic
Conditions
Anoxic
Conditions
Take Home Messages
¾ There is more than one way to be alive –
energy and carbon and electrons
¾ Microbes have most of the metabolic diversity
available
¾ Products of one organism are the substrate for
another
¾ Where metabolic pathway is energetically
favorable, a microbe has evolved to take
advantage of it
9