BIOLOGY
AMINO ACIDS
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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lead is a very dense heavy metal
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lead coordinates with the nitrogen lone pairs of amino acids
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cysteine is a super common amino acid contained in most proteins
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None of the above
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Detailed explanation-1: -Positive test: Formation of black precipitate indicate the presence of sulfur-containing amino acid. Negative test: No formation of black precipitate indicate the absence of sulfur-containing amino acid.
Detailed explanation-2: -Positive test: A positive test in the Lead sulfide test is represented by the formation of black precipitate at the bottom of the test tube. This indicates the presence of cysteine or cystine in the solution.
Detailed explanation-3: -Cysteine plays a critical role in protein structure by virtue of its ability to form inter-and intrachain disulfide bonds with other cysteine residues. Most disulfide linkages are found in proteins destined for export or residence on the plasma membrane.
Detailed explanation-4: -The test is positive for sulfur if the paper turns dark brown or black after exposure to the fumes from the sample and then turns white after exposure to hydrogen peroxide.