Transcript Document

Metabolism IV:
VI. Anaerobic respiration
VII. Chemolithotrophy
VIII. Anabolism
349
VI. Anaerobic respiration
350
Reoxidation of reduced electron carriers by a
process analogous to aerobic respiration, but
using a terminal electron acceptor other than
O2.
PMF is formed and ATP is synthesized
by electron transport phosphorylation.
Used by microbes capable of anaerobic
respiration when O2 is not available.
TB
351
A. Anaerobic respiration
external terminal electron acceptor
is not O2
eg. NO3- (nitrate), Fe3+, SO4-,
CO2, CO32-, fumarate or
another organic molecule
352
Growth
substrates
Oxidized
products
Oxidized
Reduced
electron
electron
carriers
carriers
succinate
NO2-, N2
various electron
H2S
transport chains
CH4
PMF
fumarate
NO3SO42CO2
353
1. Nitrate reduction
• a form of anaerobic respiration in which
NO3- is the terminal electron acceptor
• used by Escherichia coli and some
other microorganisms when O2 is absent
NO3
nitrate
reductase
NO2
-
354
2. Denitrification
reduction of nitrate all the way to N2
through anaerobic respiration
NO3
denitrification
N2
gas
Important in agriculture and sewage
treatment
3. Respiration with sulfur or sulfate
355
• elemental sulfur or SO42- is the
terminal electron acceptor
2SO4
0
S
reduction
H2S
H2S
smelly gases
B. Less free energy is released in anaerobic 356
respiration than in aerobic respiration
Oxidized form / Reduced form
CO2 / glucose (C6H12O2)
2 H+ / H 2
NAD+ / NADH
SO42- / H2S
pyruvate / lactate
fumarate / succinate
NO3- / NO2O2 / H2O
Reduction potential
Eo' (Volts)
(- 0.43)
(- 0.42)
(- 0.32)
(- 0.22)
(- 0.19)
(+ 0.03)
(+ 0.42)
(+ 0.82)
VII. Chemolithotrophy
Use of inorganic compounds as
the energy source (primary
electron donor)
H2 + 1/2 O2
357
H2O
Many chemolithotrophs use O2 as
the terminal electron acceptor
A. Examples of chemolithotrophs
358
H2
H2 S
2+
Fe
NH3
hydrogen-oxidizing bacteria
sulfide-oxidizing bacteria
iron-oxidizing bacteria
ammonia-oxidizing bacteria
NO2-
nitrite-oxidizing bacteria
(NH3  NO2- )
(NO2-
 NO - )
3
1. Example of chemolithotrophy:
aerobic sulfide (H2S) oxidation
H2S + 2 O2  SO4 +
2-
359
+
2H
inorganic
electron donor
Boiling sulfur pot, Yellowstone National Park
360
2. Examples of chemolithotrophy:
ammonia oxidation and nitrite oxidation
Ammonia oxidizer
NH3  NO2-
Nitrite oxidizer
NO2-  NO3-
B. Possible metabolic strategies for
generating energy on early earth
anaerobic chemolithotrophy
fermentation
anaerobic respiration
anoxygenic photosynthesis
361
A hypothetical primitive energygenerating system on early earth
Proton motive
force (PMF)
2 H+
H2
primitive
hydrogenase
2
362
primitive
ATPase
Out
Cytoplasmic
membrane
e
inorganic electron
acceptor (not O2)
In
ADP
+ Pi
ATP
VIII. Anabolism (Biosynthesis)
Nutrients
363
Waste
Energy
Anabolism
Macromolecules and
other cell components
Energy
Catabolism
Nutrients
Energy source
(eg. sugar or H2)
364
Cells are made of molecules.
Polysaccharides
Proteins
Lipids
Nucleic acids
small molecules
A. Building cell components requires
energy (ATP)
reductant (NADPH)
a source of carbon
a source of nitrogen
some P and other nutrients
CHONPS
365
366
B. Classification of organisms according to
energy source
chemoorganotroph
phototroph
(organic chemical) chemolithotroph (light)
(inorganic chemical
e.g. H2S, H2, NH3)
carbon source
heterotroph
autotroph
367
C. Cell carbon
organic carbon source (e.g. glucose)
glycolysis,
heterotrophs
TCA
nucleotides
lipid
Cell carbon:
P, NH3
sugars
fatty
acetyl CoA NH
3
acids
organic acids
amino
acids
autotrophs
CO2
nucleic
acids
protein
368
D. Sugar / polysaccharide metabolism
Sugars are needed for
polysaccharides (cell wall, glycogen)
nucleic acids (DNA, RNA)
+
small molecules (ATP, NAD(P)
cAMP, coenzymes, etc.)
O
hexoses
O
pentoses
1. UDP-glucose is a precursor to
polysaccharides and peptidoglycan.
HOCH2
O
O
O
O


O= P-O — P-O- CH2


OO-
(don't memorize structure)
369
OH
NH
O
OH
N
O
UDP =
uridine
diphosphate
2. Gluconeogenesis
370
A pathway for making glucose-6-P
from noncarbohydrate sources
(e.g. acids from TCA).
3. Gluconeogenesis is the reversal of 371
glycolysis starting with PEP, but with a
few different enzymes.
glucose-6-P
gluconeogenesis
PEP
pyruvate
CO2
OAA
TCA
succinate
4. Pentose phosphate pathway
a. makes pentoses (ribulose-5-P)
from the decarboxylation of
glucose-6-P
b. also makes NADPH for
biosynthetic reactions
372
373
5. Deoxyribonucleotides for DNA are
made from the reduction of the 2'hydroxyl of ribonucleotides.
NH2
N
P P P OCH2
O N
ATP
NH2
N
N
N
O
P P P OCH2
O N
OH OH
NADPH
OH H
NADP+
N
N
O
deoxyATP
Sugar summary
glycolysis
glucose

pyruvate
glucose-6-P

glucose-1-P
UTP

UDP-glucose
Gluconeogenesis TCA374

PEP  OAA
pentose phosphate pathway
(uridine diphosphoglucose)
ribulose-5-P
ribose-5-P
ribonucleotides RNA
NADPH
NADP+
polysaccharides peptidoglycan, deoxyribocell walls
nucleotides  DNA
E. Amino acid biosynthesis
375
1. Requires an acid (carbon skeleton)
and an amino group
amino
group
O
C – OH
H2 N – C – H
R
carboxylic acid
2. Some carbon skeletons are made 376
in glycolysis and the TCA cycle
5 main amino acid precursors
a. -ketoglutarate (5C)
b. oxaloacetate (4C)
c. pyruvate (3C)
d. phosphoglycerate (3C)
e. PEP (3C), (erythrose-4-P)
Carbon skeletons for amino acids
(glucose)
 phosphoglycerate
 PEP
CO2
(acCoA)
 pyruvate
 OAA
TCA
-KG
377
3. The amino group for glutamate 378
can come directly from ammonia.
O
C-O
O=C
CH2
CH2
COO-
O
NH3
+ C-O
H3N - C - H
CH2
+
CH2
NADP
NADPH
COO-
-ketoglutarate
glutamate
379
4. The amino group for most other
amino acids comes from glutamate
through transamination (amino transfer).
O
C - O glutamate
O=C
CH2
COO
oxaloacetate (OAA)
O
-ketoglutarate
C
O
+
H3N - C - H
CH2
COO
aspartate
F. Purine and pyrimidine
is very complex.
380
biosynthesis
1. The carbons and nitrogens come
from amino acids, NH3, CO2, and
formyl (HCOO-) groups.
N
N
*
C
C
N
N
from formyl
* attached to
folic acid
2. Folic acid carries the formyl
groups in purine biosynthesis.
381
3. Sulfanilamide is a "growth factor
analog" that inhibits purine
biosynthesis by inhibiting the
production of folic acid.
382
D. Fatty acids
1. In general, saturated fatty acids
are built two carbons at a time
from acetyl CoA.
ATP, NADPH
palmitic acid
2. Unsaturated fatty acids
• have 1 or more cis-double bonds
• increase fluidity of membranes
383
COO-
3. Acetyl CoA and succinyl CoA and
play important roles in anabolism.
acetyl CoA

succinyl CoA 
384
fatty acid biosynthesis
heme biosynthesis
Study objectives
385
1. Understand anaerobic respiration and the examples presented in class.
Define nitrate reduction, denitrification, sulfate reduction.
2. Understand chemolithotrophy and the examples presented in class.
3. Examples of integrative questions:
Compare and contrast aerobic respiration, anaerobic respiration,
chemolithotrophy, and fermentation. Given the description of a catabolic
strategy, be prepared to identify the type of metabolism being used.
Contrast sulfate reduction and sulfide oxidation.
4. Be able to classify microorganisms based on energy source and carbon
source.
5. Understand the roles of glycolysis and the TCA cycle in the synthesis of
cellular macromolecules.
6. What type of polymers are synthesized from UDP-glucose?
7. What are the functions of gluconeogenesis and the pentose phosphate
pathway?
8. How are deoxyribonucleotides for DNA made from ribonucleotides?
386
10. Know the sources of carbon and nitrogen for amino acid biosynthesis.
How are amino groups transferred to acids to make amino acids?
11. Understand the role of folic acid in nucleotide biosynthesis.
12. How does sulfanilamide inhibit the growth of microorganisms?
13. Humans do not make their own folates. Why is the drug
sulfanilamide toxic to certain microorganisms but not to humans?
14. Know the anabolic roles of acetyl CoA and succinyl CoA as described in
class.