Biosynthesis Also known as anabolism Construction of complex molecules from simple precursors Energy...
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Transcript of Biosynthesis Also known as anabolism Construction of complex molecules from simple precursors Energy...
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 phosphoadenosine-5-phosphosulfate
Sulfate is then reduced to sulfite (SO3
2) 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 malonyl-CoA 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