Question 1

Which of the following statements best describes the difference between the genome and the proteome?

Accepted Answer

The proteome is the complete set of proteins expressed and varies with cell type and environment, while the genome is the complete set of genes and is largely static.

Question 2

A researcher wants to separate proteins based on their net charge. Which technique should they use?

Accepted Answer

Isoelectric focusing

Question 3

During SDS-PAGE, proteins are separated primarily based on which property?

Accepted Answer

Molecular mass

Question 4

Which immunological technique is commonly used to detect and quantify specific proteins after separation by SDS-PAGE?

Accepted Answer

Western blot

Question 5

A protein is hydrolyzed and its amino acids are separated by ion-exchange chromatography. Which reagent is used to quantify the amino acids?

Accepted Answer

Fluorescamine

Question 6

Edman degradation is used to determine the primary structure of a protein by:

Accepted Answer

Removing one amino acid at a time from the amino end of a peptide.

Question 7

Affinity chromatography relies on which principle to purify a specific protein?

Accepted Answer

Specific binding of the protein to a ligand attached to a matrix

Question 8

In the Cuatrecasas experiment, why was Sepharose chosen as the matrix for affinity chromatography?

Accepted Answer

It is a bead form of a polysaccharide that is inert and can be easily modified.

Question 9

Why did the Cuatrecasas team use diisopropylphosphofluoridate (DIFP) in their experiment with chymotrypsin?

Accepted Answer

To covalently modify the active site and test if the inhibitor binds elsewhere on the enzyme.

Question 10

A peptide fails to undergo hydrolysis when treated with carboxypeptidase and also shows no modified N-terminal amino acid after fluorescamine treatment. What is the most likely structure of this peptide?

Accepted Answer

It is a cyclic peptide with no free N- or C-terminus.

Question 11

If a peptide antibiotic has a molecular weight of 1100 daltons and the average amino acid residue weighs about 110 daltons, how many amino acids are likely present in the peptide?

Accepted Answer

$$\frac{1100}{110} = 10$$

Question 12

Which method would be most appropriate for determining the evolutionary relationship between two proteins?

Accepted Answer

Analyzing their amino acid sequences

Question 13

A protein sample is analyzed by mass spectrometry. What information can be obtained from this technique?

Accepted Answer

Protein mass, identity, and primary structure

Question 14

Which of the following is NOT a common method for separating proteins based on their physical properties?

Accepted Answer

Dialysis

Question 15

A protein is released from an affinity column by treatment with 0.1 M acetic acid at pH 3. What is the most likely reason for this release?

Accepted Answer

The acidic conditions disrupt the binding between the protein and the ligand.

Question 16

Which of the following best explains why a small amount of DIFP-modified chymotrypsin still binds to the affinity column?

Accepted Answer

DIFP modification is incomplete, leaving some active sites unmodified.

Question 17

Which technique would you use to separate a mixture of proteins based on their size under native (non-denaturing) conditions?

Accepted Answer

Gel filtration chromatography

Question 18

A protein sample absorbs strongly at 280 nm during purification. What does this indicate?

Accepted Answer

The protein contains aromatic amino acids such as tryptophan and tyrosine.

Question 19

Which of the following steps is essential before determining the amino acid sequence of a large polypeptide?

Accepted Answer

Cleaving the polypeptide into shorter fragments using specific reagents

Question 20

A scientist is using ion-exchange chromatography to separate amino acids after protein hydrolysis. What property of amino acids is exploited in this technique?

Accepted Answer

Their net charge at a given pH

Biochemistry: A Short Course 5

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