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Ordering Cleaved Fragments quiz

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  • Why is Edman degradation limited to sequencing small peptides?
    Edman degradation can only sequence peptides with fewer than 50 amino acids. Larger proteins must be cleaved into smaller fragments first.
  • What is the main challenge after sequencing individual peptide fragments from a cleaved protein?
    The main challenge is determining the correct order of the peptide fragments in the original protein sequence.
  • Why is using only one cleavage method, such as cyanogen bromide, often insufficient for determining the original protein sequence?
    Using only one cleavage method can produce fragments that fit multiple possible sequences, making it impossible to determine the correct order with certainty.
  • How does cyanogen bromide cleave proteins?
    Cyanogen bromide cleaves proteins at the carboxyl side of methionine residues.
  • What is the benefit of using multiple cleavage techniques on the same protein?
    Multiple cleavage techniques generate overlapping fragments, which help reveal the original protein sequence by aligning shared amino acids.
  • What is the typical minimum number of cleavage techniques required to accurately order peptide fragments?
    At least two different cleavage techniques are typically required to accurately order peptide fragments and determine the protein sequence.
  • What is the first step in sequencing a large protein using Edman degradation?
    The first step is to cleave the large protein into smaller peptide fragments.
  • After cleaving a protein, what must be done before sequencing with Edman degradation?
    The peptide fragments must be separated before sequencing each one individually with Edman degradation.
  • How do overlapping fragments from different cleavage methods help in sequencing?
    Overlapping fragments allow for alignment of shared amino acids, confirming the order of fragments in the original sequence.
  • What is the strategy for starting to order fragments from multiple cleavage methods?
    The strategy is to start with the longest fragment and then look for overlaps with other fragments to build the sequence.
  • What does the presence of overlapping amino acids in fragments indicate?
    Overlapping amino acids confirm the correct alignment and order of fragments in the original protein sequence.
  • Why might two different fragment orders both seem valid after a single cleavage method?
    Because the cleavage may produce the same set of fragments for different possible sequences, making it ambiguous without additional information.
  • What role does chymotrypsin play in sequencing proteins?
    Chymotrypsin is a protease used as a second cleavage technique to generate a different set of peptide fragments for overlap analysis.
  • What is the outcome when two cleavage methods are used and their fragments are overlapped?
    The original protein sequence can be determined by aligning the overlapping regions of the fragments from both methods.
  • What is the main takeaway about ordering cleaved fragments for protein sequencing?
    Using two or more cleavage methods is essential to accurately order fragments and reveal the original protein sequence.