A small protein was isolated in the lab, and the following fragments were sequenced using the Edman degradation. Determine the polypeptide sequence of this small protein.
The correct answer and explanation is:
To determine the correct polypeptide sequence of a small protein using Edman degradation, the actual fragment sequences must be provided. Since the fragments are not included in your question, I will explain how to determine the full sequence once the fragments are known and also provide a sample answer using a hypothetical set of fragments to guide you.
Correct Answer (Based on Sample Fragments):
Polypeptide sequence: GLY-ALA-VAL-LEU-ARG
Explanation:
Edman degradation is a method used to sequence amino acids in a peptide. It works by labeling and cleaving the N-terminal (first) amino acid of a peptide, which is then identified, and the process repeats with the remaining peptide chain. This technique works best for short peptides or fragments obtained from breaking down a longer protein.
To determine the full sequence of a protein, scientists often cleave the protein using specific enzymes such as trypsin or chymotrypsin. These enzymes cut the protein at known amino acid residues, producing overlapping fragments. Each of these fragments is then sequenced individually using Edman degradation. Because the fragments overlap, the original sequence of the entire protein can be deduced.
Here is an example using hypothetical fragments:
- Fragment 1: GLY-ALA-VAL
- Fragment 2: ALA-VAL-LEU
- Fragment 3: VAL-LEU-ARG
By aligning the overlapping parts:
- Fragment 1 ends in VAL
- Fragment 2 starts with ALA-VAL and continues with LEU, matching Fragment 1
- Fragment 3 continues from VAL-LEU and ends in ARG
From this, the correct order is:
GLY-ALA-VAL-LEU-ARG
This method requires careful alignment and comparison of overlapping sequences