Biosynthesis
Also known as anabolism
Construction of complex
molecules from simple
precursors
Energy derived from catabolism
used in biosynthesis
Sulfur assimilation
Sulfur is required for the formation of cysteine, methionine and
many cofactors
Sulfate (SO42) is often used as a source of sulfur
Sulfate must be reduced before assimilation
 assimilatory sulfate reduction
Sulfur assimilation
Sulfate is activated by the
formation of phosphoadenosine5-phosphosulfate
Sulfate is then reduced to sulfite
(SO32) then to hydrogen sulfide
(H2S)
Sulfur assimilation
Cysteine is then formed from
H2S and used in the formation of
other sulfur containing molecules
Nitrogen assimilation
Nitrogen required for proteins, nucleic acids and other important
cell constituents
Most microorganisms are incapable of using nitrogen gas as a
nitrogen source
They must therefore incorporate either ammonia (NH3) or nitrate
(NO3)
Ammonia incorporation
Ammonia is easily incorporated because it is more highly
reduced than other forms of nitrogen
Can be combined with pyruvate to form alanine or ketoglutarate to form glutamate
Ammonia incorporation
Ammonia can also be
incorporated using two enzymes
acting in sequence
Glutamine synthetase and
glutamate synthetase
Ammonia incorporation
Ammonia used to synthesize glutamine from glutamate
Amino group of glutamine transferred to -ketoglutarate to form
2 molecules of glutamate
Amino group can then be transferred to form other amino acids
Assimilatory nitrate reduction
Nitrate must be converted to
ammonia before incorporation
into organic compounds
Nitrate is first reduced to nitrite
by nitrate reductase
Assimilatory nitrate reduction
Nitrite is reduced to ammonia by
nitrite reductase
Ammonia is then incorporated
into organic material
Nitrogen fixation
The reduction of gaseous nitrogen to ammonia
Rate of this process often limits plant growth
Carried out by a small number of microorganisms
Nitrogen fixation
Reduction of nitrogen to
ammonia is catalyzed by
nitrogenase
Sequential addition of electron
pairs results in formation of 2
molecules of ammonia from 1
molecule of N2
Nitrogen fixation
Energetically expensive:
requires 8 electrons and 16 ATPs
Synthesis of amino acids
Carbon skeletons derived from
acetyl-CoA and intermediates of
glycolysis, the TCA cycle and
the pentose phosphate pathway
Synthesis of amino acids
Synthesis of amino acids
Common intermediates are used
to synthesize families of related
amino acids
Synthesis of amino acids
Common intermediates are used
to synthesize families of related
amino acids
Anapleurotic reactions
TCA cycle intermediates used
for biosynthesis could be
depleted
Anapleurotic reactions serve to
replenish cycle intermediates
Anapleurotic reactions
Most microorganisms replace
TCA cycle intermediates by CO2
fixation
Different from autotrophs since
only used to replace
intermediates
Pyruvate or PEP used as acceptor
molecule to form oxaloacetate
Glyoxylate pathway
Some microorganisms can use
acetate as the sole carbon source
Synthesize TCA cycle
intermediates using the
glyoxylate pathway
Modified TCA cycle
Glyoxylate pathway
Isocitrate converted to succinate
and glyoxylate
Glyoxylate combines with
acetyl-CoA to form oxaloacetate
Prevents loss of acetyl-CoA
carbons as CO2
Synthesis of purines and pyrimidines
Cyclic nitrogen containing bases that are used in the synthesis of
ATP, DNA, RNA and other cell components
Purines contain two joined rings: adenine and guanine
Pyrimidines have a single ring: cytosine, thymine and uracil
Synthesis of purines and pyrimidines
Purine or pyrimidine joined to
pentose sugar (ribose or
deoxyribose) = nucleoside
Nucleoside + one or more
phosphate group = nucleotide
Synthesis of purines
Seven different molecules
contribute parts to final skeleton
Synthesis of purines
Inosinic acid is the first common
intermediate
Adenosine and guanosine
monophosphates formed
Nucleoside diphosphates and
triphosphates formed by
phosphate transfers from ATP
Synthesis of pyrimidines
Aspartic acid and carbamoyl
phosphate combine
Eventually converted to orotic
acid
Ribose then added and
decarboxylation results in uridine
monophosphate
Synthesis of fatty acids
Uses acetyl-CoA and malonylCoA as substrates
Malonyl-CoA formed from
acetyl-CoA and CO2
Both are transferred to acyl
carrier protein (ACP)
Synthesis of fatty acids
Malonyl-ACP reacts with fatty
acyl-ACP to yield CO2 and fatty
acyl-ACP + 2 carbons
Followed by 2 reductions and a
dehydration
Fatty acyl-ACP then ready to
accept another malonyl-ACP
Synthesis of fatty acids vs. -oxidation
Reverse process except uses CoA as carrier rather than ACP
Synthesis of lipids
Dihydroxyacetone phosphate
reduced to glycerol 3-P
Glycerol 3-P combines with 2
fatty acids to form phosphatidic
acid
Attachment of third fatty acid
yields triglyceride
Synthesis of lipids
Phosphatidic acid attached to
cytidine diphosphate (carrier)
Reacts with serine to form
phosphatidylserine
Decarboxylation yields
phosphatidylethanolamine