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Sulphur is needed for the synthesis of
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Amino acids (cysteine & methionine)and several coenzymes(eg coenzyme A & biotin)
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It may be obtained from
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Two sources
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Many microorganisms use cysteine and methionine obtained from either
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External sources or intracellular amino acids reserves
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In addition sulphate can provide sulphur for
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Biosynthesis
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Sulphur atom in sulphate is more oxidised than it is in
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Cysteine and other organic molecules
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Thus sulphate must be reduced
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Before it can be assimilated
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This process is Known as
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Assimilatory sulphate reduction
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To distinguish it from the dissimilatory sulphate reduction that takes place when
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Sulphate acts as an electron acceptor during anaerobic respiration
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Assimilatory sulphate reduction involves
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Sulphate activation through formation of phosphoadenosine 5’-phosphosulphate followed by reduction of the sulphate
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In this process sulphate is first reduced to
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Sulphite and then to hydrogen sulphide
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Cysteine can be synthesized from hydrogen sulphide
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In two ways
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Process 1 :Fungi appear to combine hydrogen sulfide with serine to form
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Cysteine
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Process 2:wheras many bacteria join
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Hydrogen sulphide With O- acetylserine instead
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