Question 1

Which of the following best describes the main purpose of Edman degradation in protein sequencing?

Accepted Answer

To sequentially remove and identify N-terminal amino acids from a peptide.

Question 2

A researcher wants to determine the sequence of a protein but finds that the protein contains multiple polypeptide chains linked by disulfide bonds. What should be the first step before sequencing?

Accepted Answer

Reduce and separate the polypeptide chains by breaking disulfide bonds.

Question 3

Which reagent is commonly used for complete hydrolysis of peptide bonds in proteins, resulting in free amino acids?

Accepted Answer

6M HCl

Question 4

Which of the following statements about chemical cleavage of proteins is correct?

Accepted Answer

Chemical cleavage can be used to break peptide bonds at specific amino acid residues.

Question 5

A scientist uses cyanogen bromide to cleave a protein. Which amino acid residue is specifically targeted by this reagent?

Accepted Answer

Methionine

Question 6

Which of the following best explains why proteins are often fragmented before sequencing?

Accepted Answer

Fragmentation produces smaller peptides that can be sequenced more efficiently.

Question 7

Which technique would you use to determine the amino acid composition (but not the sequence) of a protein?

Accepted Answer

Amino acid hydrolysis with $$6M\ HCl$$

Question 8

A protein is treated with trypsin, which cleaves at the carboxyl side of lysine and arginine residues. What is the expected result?

Accepted Answer

The protein is fragmented into peptides ending with lysine or arginine.

Question 9

Which of the following is NOT a direct protein sequencing technique?

Accepted Answer

Western blotting

Question 10

During Edman degradation, which chemical is used to label the N-terminal amino acid?

Accepted Answer

Phenyl isothiocyanate

Question 11

A protein sample is subjected to $$6M\ HCl at $$high temperature. Which of the following best describes the outcome?

Accepted Answer

The protein is completely hydrolyzed to free amino acids.

Question 12

Which of the following steps is essential before sequencing a protein with multiple subunits?

Accepted Answer

Breaking disulfide bonds to separate subunits

Question 13

Which of the following best describes the result of peptide cleavage by a specific protease?

Accepted Answer

Cleavage at specific amino acid residues

Question 14

Why is it important to know the primary structure of a protein?

Accepted Answer

It dictates all other levels of protein structure and function.

Question 15

Which of the following is a limitation of Edman degradation?

Accepted Answer

It is ineffective for peptides longer than about 50 residues.

Question 16

A protein is first reduced to break disulfide bonds, then fragmented with trypsin, and finally sequenced by Edman degradation. What is the main advantage of this approach?

Accepted Answer

It allows sequencing of large proteins by analyzing smaller peptide fragments.

Question 17

Which of the following best matches the reagent to its function in protein sequencing?

Accepted Answer

6M HCl: Hydrolyzes all peptide bonds

Question 18

Which of the following steps is NOT typically part of the direct protein sequencing workflow?

Accepted Answer

Complete hydrolysis to free amino acids for sequence determination

Question 19

A protein is digested with a protease that cleaves at the carboxyl side of arginine residues. Which of the following best describes the resulting fragments?

Accepted Answer

Peptides ending with arginine

Question 20

Which of the following is a reason why multiple cleavage techniques are used in protein sequencing?

Accepted Answer

To generate overlapping peptide fragments for accurate sequence assembly.

Direct Protein Sequencing: Techniques and Applications

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