Answer:
Sulphur, because it is the major building element for protein synthesis.
Explanation:
A diet of only canned spaghetti has no Sulphur contents ( the only mineral in spaghetti is iron( 4mg ). But most enriched canned spaghetti contains 4g protein. However the sulphur in this protein would have been broken down during heat processing and packaging to sulphides(picked up by sulphur resistant enamel in the can). Therefore she has been on no protein diet but just on purely carbohydrate diet, hence protein deficiency.
Consequently,her body sulphur content is very low. Sulphur is the major content of some amino acids in the body of animals; especially in formation of methionine and Cysteine structures.
The sulphur content of Cysteine residues provides disulphide bridges(S-S) in polypeptide chains which is important for assemblage,storage and stability (as covalent bonds) of protein structure needed for protein synthesis. In addition, Methionine is an essential amino acid, needed in protein synthesis,
Thus lack of sulphur results in lack of methionine and cystenine and therefore ,deficiency of protein .
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