BIOLOGY
AMINO ACIDS
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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hydroxyl group
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sulfhydryl group
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amide group
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carboxyl group
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Detailed explanation-1: -SO WHY CYSTEINE IS SPECIAL? Because it has a very reactive sulfhydryl group at its side chain. This puts cysteine in special position that cannot be replaced or substituted by any other amino acid. Because disulfide bridges formed by cysteine residues are permanent component of protein primary structure.
Detailed explanation-2: -Unlike methionine, which has its sulfur in a relatively less reactive thioether form, the thiol (or “sulfhydryl”) group of cysteine is ionizable, with a negatively-charged thiolate group being generated after deprotonation, boosting its reactivity (Fig. 1).
Detailed explanation-3: -Six amino acids have side chains that are polar but not charged. These are serine (Ser), threonine (Thr), cysteine (Cys), asparagine (Asn), glutamine (Gln), and tyrosine (Tyr).