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...
![Page 1: Biosynthesis Also known as anabolism Construction of complex molecules from simple precursors Energy derived from catabolism used in biosynthesis.](https://reader036.fdocuments.us/reader036/viewer/2022062313/56649cc15503460f94988729/html5/thumbnails/1.jpg)
Biosynthesis
Also known as anabolism
Construction of complex molecules from simple precursors
Energy derived from catabolism used in biosynthesis
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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
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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)
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Sulfur assimilation
Cysteine is then formed from H2S and used in the formation of other sulfur containing molecules
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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
)
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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
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Ammonia incorporation
Ammonia can also be incorporated using two enzymes acting in sequence
Glutamine synthetase and glutamate synthetase
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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
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Assimilatory nitrate reduction
Nitrate must be converted to ammonia before incorporation into organic compounds
Nitrate is first reduced to nitrite by nitrate reductase
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Assimilatory nitrate reduction
Nitrite is reduced to ammonia by nitrite reductase
Ammonia is then incorporated into organic material
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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
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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
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Nitrogen fixation
Energetically expensive: requires 8 electrons and 16 ATPs
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Synthesis of amino acids
Carbon skeletons derived from acetyl-CoA and intermediates of glycolysis, the TCA cycle and the pentose phosphate pathway
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Synthesis of amino acids
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Synthesis of amino acids
Common intermediates are used to synthesize families of related amino acids
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Synthesis of amino acids
Common intermediates are used to synthesize families of related amino acids
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Anapleurotic reactions
TCA cycle intermediates used for biosynthesis could be depleted
Anapleurotic reactions serve to replenish cycle intermediates
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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
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Glyoxylate pathway
Some microorganisms can use acetate as the sole carbon source
Synthesize TCA cycle intermediates using the glyoxylate pathway
Modified TCA cycle
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Glyoxylate pathway
Isocitrate converted to succinate and glyoxylate
Glyoxylate combines with acetyl-CoA to form oxaloacetate
Prevents loss of acetyl-CoA carbons as CO2
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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
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Synthesis of purines and pyrimidines
Purine or pyrimidine joined to pentose sugar (ribose or deoxyribose) = nucleoside
Nucleoside + one or more phosphate group = nucleotide
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Synthesis of purines
Seven different molecules contribute parts to final skeleton
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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
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Synthesis of pyrimidines
Aspartic acid and carbamoyl phosphate combine
Eventually converted to orotic acid
Ribose then added and decarboxylation results in uridine monophosphate
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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)
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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
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Synthesis of fatty acids vs. -oxidation
Reverse process except uses CoA as carrier rather than ACP
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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
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Synthesis of lipids
Phosphatidic acid attached to cytidine diphosphate (carrier)
Reacts with serine to form phosphatidylserine
Decarboxylation yields phosphatidylethanolamine