Q.17 In the process of protein sequencing, trypsin and chymotrypsin are used for generating fragments.
Select tryptic peptide from the list –
- Try
- Phe
- Trp
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Trypsin cleaves proteins specifically after lysine (Lys), making it the correct tryptic peptide from the options. Phe and Trp are targeted by chymotrypsin instead.
Question Breakdown
This MCQ tests enzyme specificity in protein sequencing. Trypsin generates “tryptic peptides” by cutting at basic residues, while chymotrypsin targets aromatic ones. Lys is the sole match here.
Option Analysis
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Phe (Phenylalanine): Aromatic side chain; chymotrypsin cleaves after it, not trypsin.
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Trp (Tryptophan): Aromatic; cleaved by chymotrypsin.
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Lys (Lysine): Basic residue; trypsin cleaves on its carboxyl side (unless followed by proline).
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Try: Likely a distractor for “tryptic” or mislabeled Trp/Tyr; not a standard trypsin site.Lys
In protein sequencing, generating tryptic peptide fragments using trypsin is essential for determining amino acid order, especially in competitive exams like GATE Life Sciences. This process relies on trypsin’s precise cleavage after basic residues like lysine (Lys), distinguishing it from chymotrypsin’s action on aromatic amino acids such as Phe and Trp.
Trypsin Specificity
Trypsin, a serine protease, hydrolyzes peptide bonds at the carboxyl side of lysine (Lys) or arginine (Arg), producing tryptic peptides ideal for mass spectrometry analysis. This specificity arises from its S1 pocket binding positively charged side chains. Exceptions occur if proline follows, blocking cleavage.
Chymotrypsin Role
Chymotrypsin complements trypsin by cleaving after bulky hydrophobics: phenylalanine (Phe), tryptophan (Trp), or tyrosine (Tyr). Overlapping fragments from both enzymes allow full sequence reconstruction in protein sequencing workflows.
Exam Relevance
For GATE Life Sciences PYQs, identify tryptic peptides by Lys/Arg sites. Here, Lys is correct; Phe/Trp suit chymotrypsin. Practice with sample proteins to master fragmentation patterns.
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