Chapter7 Microbial metablism
Catabolism,anabolism
Fermentation
Respiration
Nitrogen fixtation
The synthesis of peptiglydogen
7.1 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
7.2 Fermentation,
The Embden-Meyerhof Pathway
A fermentation is an internally balanced
oxidation-reduction reaction in which some
atoms of the energy source (electron donor)
become more reduced whereas others become
more oxidized,and energy is produced by
substrate-level phosphorylation.
Energy conservation in fermentation and respiration
Embden-Meyerhof pathway
Glycolysis,A common biochemical pathway for the
fermentation of glucose is glycolysis,also named the
Embden-Meyerhof pathway for its major discoverers,Can
be divided into three major stages,
Stage I, A series of preparatory rearrangements,reactions
that do not involve oxidation-reduction and do not release
energy but that lead to the production from glucose of two
molecules of the key intermediate,glyceraldehyde 3-
phosphate,
Stage II,Oxidation-reduction occurs,energy is conserved
in the form of ATP,and two molecules of pyruvate are
formed,
Stage III,A second oxidation-reduction reaction occurs and
fermentation products (for example,ethanol and CO2,or
lactic acid) are formed.
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
6.6 Respiration and Electron Transport
The discussion of respiration deals with both the carbon
and electron transformations:
? (1) the biochemical pathways involved in the
transformation of organic carbon to CO2,
? (2) the way electrons are transferred from the organic
compound to the terminal electron acceptor,driving
ATP synthesis at the expense of the proton motive
force.
Respiration, in which molecular oxygen or some other
oxidant serves as the terminal electron acceptor.
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 -,)
(1) to accept electrons from an electron donor and
transfer them to an electron acceptor
Electron Transport
Electron transport systems are composed of membrane
associated electron carriers,These systems have two
basic functions:
(2) to conserve some of the energy released during
electron transfer for synthesis of ATP.
Biosynthesis of Peptidoglycan
Most bacterial cell walls contain a large,complex
peptidoglycan molecule consisting of long
polysaccharide chains made of alternating NAM
and NAG residues,NAM is N-acetylmuramic acid
and NAG is N-acetylglucosamine,The pentapeptide
contains L-lysine in S.aureus peptidoglycan,and
diaminopimelic acid (DAP) in E.coli,Inhibition by
bacitracin,cycloserine,and vancomycin.
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 UDP-
NAM 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 NAM-
pentapeptide to form the peptidoglycan repeat
unit.
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.
Eight stages of Peptidoglycan
synthesis
Peptidoglycan synthesis
Cytoplasm Cell wall
undecaprenol
sugar
amino
acid
Cell Membrane
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
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
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
Catabolism,anabolism
Fermentation
Respiration
Nitrogen fixtation
The synthesis of peptiglydogen
7.1 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
7.2 Fermentation,
The Embden-Meyerhof Pathway
A fermentation is an internally balanced
oxidation-reduction reaction in which some
atoms of the energy source (electron donor)
become more reduced whereas others become
more oxidized,and energy is produced by
substrate-level phosphorylation.
Energy conservation in fermentation and respiration
Embden-Meyerhof pathway
Glycolysis,A common biochemical pathway for the
fermentation of glucose is glycolysis,also named the
Embden-Meyerhof pathway for its major discoverers,Can
be divided into three major stages,
Stage I, A series of preparatory rearrangements,reactions
that do not involve oxidation-reduction and do not release
energy but that lead to the production from glucose of two
molecules of the key intermediate,glyceraldehyde 3-
phosphate,
Stage II,Oxidation-reduction occurs,energy is conserved
in the form of ATP,and two molecules of pyruvate are
formed,
Stage III,A second oxidation-reduction reaction occurs and
fermentation products (for example,ethanol and CO2,or
lactic acid) are formed.
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
6.6 Respiration and Electron Transport
The discussion of respiration deals with both the carbon
and electron transformations:
? (1) the biochemical pathways involved in the
transformation of organic carbon to CO2,
? (2) the way electrons are transferred from the organic
compound to the terminal electron acceptor,driving
ATP synthesis at the expense of the proton motive
force.
Respiration, in which molecular oxygen or some other
oxidant serves as the terminal electron acceptor.
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 -,)
(1) to accept electrons from an electron donor and
transfer them to an electron acceptor
Electron Transport
Electron transport systems are composed of membrane
associated electron carriers,These systems have two
basic functions:
(2) to conserve some of the energy released during
electron transfer for synthesis of ATP.
Biosynthesis of Peptidoglycan
Most bacterial cell walls contain a large,complex
peptidoglycan molecule consisting of long
polysaccharide chains made of alternating NAM
and NAG residues,NAM is N-acetylmuramic acid
and NAG is N-acetylglucosamine,The pentapeptide
contains L-lysine in S.aureus peptidoglycan,and
diaminopimelic acid (DAP) in E.coli,Inhibition by
bacitracin,cycloserine,and vancomycin.
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 UDP-
NAM 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 NAM-
pentapeptide to form the peptidoglycan repeat
unit.
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.
Eight stages of Peptidoglycan
synthesis
Peptidoglycan synthesis
Cytoplasm Cell wall
undecaprenol
sugar
amino
acid
Cell Membrane
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
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
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
