Download Catabolism

Microbial metablism
Catabolism, anabolism
Fermentation
Respiration
Nitrogen fixtation
The synthesis of peptiglydogen
An overview of metabolism
• Metabolism may be divided into two major
parts: catabolism and anabolism.
• Catabolism: larger and more complex
molecules are broken down into smaller,
simpler molecules with the release of
energy.
• Anabolism: the synthesis of complex
molecules from simpler ones with the
input of energy.
The
three
stages
of
catabolism
• Much of the ATP derived from the TCA cycle
comes from the oxidation of NADH and FADH2
by the electron transport chain.
•
Carbohydrates and other nutrients serve two
functions in the metabolism of heterotrophic
microorganisms:
1. They are oxidized to release energy
2. They supply carbon or building blocks for the
synthesis of new cell constituents.
• Amphibolic pathways: function both
catabolically and anabolically
SUGAR CATABOLISM
• Glycolysis (Embden, Meyerhof Parnas
Pathway)
– most bacteria
– also animals and plants
Other pathways for catabolizing
sugars
• Pentose phosphate pathway (hexose
monophosphate shunt)
– generates NADPH
– common in plants and animals
• Entner Doudoroff Pathway
– a few bacterial species
Glycolysis
NAD
NADH
Glucose
Pyruvate
C6
C3
ADP
ATP
Fermentation
The energy substrate is oxidized and degraded
without the participation of an exogenous or extrenally
derived electron acceptor.
Usually an intermediate such as pyruvate acts the
electron acceptor.
Anaerobic conditions
Two unifying themes should be kept in mind when
microbial fermentation are examined:
1.
NADH
2. Pyruvate
NAD
Short chain alcohols,
fatty acids
(C3)
(C2-C4)
Three type fermentation of
Saccharomyces cerevisiae
I: pyruvateacetaldehydeethanol
II: pH7: glycerol
III: NaHSO3
Lactic acid fermentation
• The reduction of pyruvate to lactate
• Homofermentative（同型发酵的）
group: produces only lactic acid as sole
product
• Heterofermentative（异型发酵的）
group: produces ethanol, CO2 and lactic
acid
Respiration
Energy-yielding metablism can make use of
exogenous or externally derived electron
acceptors.
Two different type:
aerobic respiration: the final
electron acceptor is oxygen
anaerobic respiration: most often is
inorganic such as NO3-, SO42-, CO2 , Fe3+,
SeO42 -,)
Anaerobic Respiration =
Glycolysis + Fermentation
NAD
NADH
ATP
NADH
NAD
Krebs Cycle (C4-C6 intermediate compounds)
NAD
Pyruvate
NADH
3CO2
(C3)
(C1)
Oxidative phosphorylation
NADH
NAD
O2
H2O
ADP
ATP
Aerobic Respiration =
Glycolysis +
Krebs Cycle/oxidative phosphorylation
•
Pyruvate to CO2
–
NAD to NADH
–
glycolysis
– Krebs cycle
•
Oxidative phosphorylation
–
NADH to NAD
– ADP to ATP
Oxidative phosphorylation
• converts
O2 to H20 (oxidative)
• converts ADP to ATP (phosphorylation)
• electron transport chain
• ubiquinones/cytochrome intermediates
Sugar as sole carbon source
Krebs Cycle
C6
Pyruvate
(C3)
-CO2
Acetate
(C2)
+ CO2
Pyruvate
(C3)
C4
FATTY ACIDS AS SOLE CARBON
SOURCE
Krebs Cycle
C6
Fatty acids
Acetate
(C2)
C4
C4 + C2
The glyoxylate cycle
C3
C6
C6
C2
+
C5
C4
C2
C2
C4
C4
C4
Krebs Cycle
– biosynthetic
– energy producing
• Removal of intermediates
– must be replenished.
• Unique enzymatic replenishment pathway
– sugars
– fatty acids
Nitrogen fixation
The reduction of atmospheric gaseous nitrogen
to ammonia is callled
nitrogen fixation.
Nitrogen fixation occurs in:
1. Free-living bacteria.(Azotobacter)
2. Bacteria living in symbiotic association with
plants such as legumes(Rhizobium)
3. cyanobacteria
Nitrogenase
Consistiong of two major protein
components: a MoFe protein joined
with one or two Fe proteins.
1. The MoFe protein contains 2 atoms of
molybdenum and 28 to 32 atoms of iron;
2. The Fe protein has 4 iron atoms
Mechnisms of anti-oxygen
Nitrogenase is quite sensitive to O2 and
must be protected from O2
inactivation within the cell.
1.Respiration protection
2.Hetercyst formation
3.Membrane
Nitrogen reduction
N2+8H++8e-+16ATP2NH3+H2+16ADP+16Pi
Root Nodule Bacteria and
Symbiosis with legumes
Soybean root nodules
Unnodulated soybean
Nodulated soybean
Steps in the formation of
root nodule in a legume
infected by Rhizobium
Peptidoglycan synthesis
Staphylococcus aureus
Two carriers participate:
uridine diphosphate (UDP) and bactoprenol
Bactoprenol is a 55-carbon alcohol that
attaches to NAM by a pyrophosphate group
and moves peptidoglycan components
through the hydrophobic membrane
Eight stages of Peptidoglycan
synthesis
1. The formation of UDP-NAM and UDP-NAG
2. Amino acids are sequentially added to UDPNAM to form the pentapeptide chain.
3. The NAM-pentapeptide is transferred from
UDP to a bactoprenol phosphate at the
membrane surfacre.
4. UDP-NAG adds NAG to the NAMpentapeptide to form the peptidoglycan repeat
unit.
Eight stages of Peptidoglycan
synthesis
5. Repeat unit is transported across the
membrane to its outer surface by the
bactoprenol pyrophosphate carrier.
6. The peptidoglycan unit is attached to the
growing end of a peptidoglycan chain to
lengthen it by one repeat unit.
7. The bactoprenol carrier returns to the inside
of the membrane. A phosphate is released.
8. Peptide cross-links between the peptidoglycan
chains are formed by transpeptidation.
Peptidoglycan synthesis
Cytoplasm
Cell Membrane
undecaprenol
sugar
amino
acid
Cell wall
Peptidoglycan Synthesis
Transport of peptidoglycan precursors across the
cytoplasmic membrane to the growing point of the cell wall
The transpeptidation reaction that lead to the final
cross-linking of two peptidoglycan chains
Penicillin inhibits this reaction
Questions
•
•
•
•
•
•
What are catabolism and anabolism?
What are Fermentation and Respiration?
Lactic acid fermentation
aerobic respiration, anaerobic respiration
Nitrogen fixation
Why is Root nodule bacteria and symbiosis
so important for legumes?
• Eight stages of Peptidoglycan synthesis