Question 1

Which method for protein concentration determination is most susceptible to interference from nucleic acids and other UV-absorbing compounds?

Accepted Answer

A280 Assay

Question 2

In SDS-PAGE, what is the primary reason that proteins are separated based solely on their size?

Accepted Answer

SDS binds to proteins, giving them a uniform negative charge and linear shape

Question 3

Which of the following statements about 2D electrophoresis is CORRECT?

Accepted Answer

It separates proteins by isoelectric point in the first dimension and by size in the second dimension

Question 4

Which reagent is used in the Edman degradation method for N-terminal sequencing of proteins?

Accepted Answer

Phenylisothiocyanate (PITC)

Question 5

A protein sample is analyzed by SDS-PAGE and shows a single band at 30 kDa. After treatment with β-mercaptoethanol, two bands at 18 kDa and 12 kDa appear. What does this indicate about the protein?

Accepted Answer

The protein is a heterodimer linked by disulfide bonds

Question 6

Which of the following best describes the principle of the Bradford assay for protein quantification?

Accepted Answer

Binding of Coomassie Brilliant Blue dye to proteins, causing a shift in absorbance

Question 7

Which enzyme would you use to generate peptides with C-terminal lysine or arginine residues for mass spectrometry analysis?

Accepted Answer

Trypsin

Question 8

In mass spectrometry, the mass-to-charge ratio ($$m/z) of an $$ion is determined by which of the following equations?

Accepted Answer

$$r = \frac{mv}{qB}$$

Question 9

Which ionization technique is most suitable for analyzing large, intact proteins while preserving post-translational modifications?

Accepted Answer

Matrix-Assisted Laser Desorption Ionization (MALDI)

Question 10

A researcher wants to determine the amino acid composition of a food protein. Which analytical sequence is most appropriate?

Accepted Answer

Hydrolysis with 6 M HCl, separation by ion exchange chromatography, quantification

Question 11

Which of the following is a limitation of the Bicinchoninic Acid (BCA) assay for protein quantification?

Accepted Answer

Interference from reducing agents and chelators

Question 12

In peptide mapping, why does trypsin digestion produce a unique peptide map for each protein?

Accepted Answer

Each protein has a unique sequence of lysine and arginine residues

Question 13

Which step in tandem mass spectrometry (MS/MS) allows for the reconstruction of a peptide's amino acid sequence?

Accepted Answer

Measuring the mass differences between fragment ions

Question 14

Which of the following best describes the main advantage of 2D electrophoresis over 1D SDS-PAGE?

Accepted Answer

It can resolve proteins with similar size but different isoelectric points

Question 15

A mass spectrometry experiment produces two peptides with identical masses but different sequences. What are these peptides called?

Accepted Answer

Isobaric peptides

Question 16

Which of the following is TRUE regarding the Kjeldahl method for protein quantification?

Accepted Answer

It measures the nitrogen content of proteins via acid digestion and titration

Question 17

Which of the following best explains why reducing agents like β-mercaptoethanol are used in SDS-PAGE?

Accepted Answer

To break disulfide bonds and fully denature proteins

Question 18

In mass spectrometry, what is the main purpose of the magnetic field in the analyzer?

Accepted Answer

To separate ions based on their mass-to-charge ratio ($$m/z)$$

Question 19

Which of the following statements about bottom-up proteomics is CORRECT?

Accepted Answer

It involves enzymatic digestion of proteins into peptides before mass spectrometry

Question 20

Which of the following is a key advantage of using mass spectrometry for protein identification in proteomics?

Accepted Answer

It provides a peptide mass fingerprint that can be matched to protein databases

Protein Analysis: Techniques and Applications in Biochemistry

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