Question 1

Which of the following best describes the main advantage of tandem mass spectrometry (MS/MS) over single-stage mass spectrometry for protein analysis?

Accepted Answer

It enables the sequencing of proteins by fragmenting selected ions and analyzing their fragments.

Question 2

In tandem mass spectrometry, what is the primary purpose of the first mass spectrometer (MS1)?

Accepted Answer

To filter and select a specific ion of interest for further fragmentation.

Question 3

A researcher uses tandem mass spectrometry to analyze a protein mixture. After the first MS, a peptide ion with $$m/z = 1,169 is $$selected and fragmented. The second MS detects fragments with $$m/z$$ values of $$1,137$$ and $$1,082. If $$the mass of the lost amino acid is $$113$$, which amino acid was cleaved off? (Amino acid masses: G = 57, A = 71, S = 87, L = 113, M = 131)

Accepted Answer

Leucine (L)

Question 4

Which combination of analytical techniques is most commonly used in tandem mass spectrometry for protein sequencing?

Accepted Answer

Mass spectrometer with a mass spectrometer

Question 5

During tandem mass spectrometry, why is it important to fragment the selected ion before the second mass analysis?

Accepted Answer

Fragmentation allows for the determination of the amino acid sequence of the peptide.

Question 6

A peptide is fragmented in a tandem mass spectrometer, and the resulting fragment ions are analyzed. If the mass difference between two consecutive fragments is $$129$$, which amino acid is likely present between these fragments? (Amino acid masses: E = 129, D = 115, G = 57, L = 113, M = 131)

Accepted Answer

Glutamic acid (E)

Question 7

In the context of tandem mass spectrometry, what does the term 'precursor ion' refer to?

Accepted Answer

The ion selected by the first mass spectrometer for fragmentation.

Question 8

A tandem mass spectrometry experiment produces a series of fragment ions with mass differences corresponding to the masses of amino acids. What information can be directly obtained from this data?

Accepted Answer

The primary sequence of the peptide.

Question 9

Which of the following best explains why tandem mass spectrometry is considered a gold standard for sequencing proteins?

Accepted Answer

It allows for the identification and sequencing of proteins even in complex mixtures.

Question 10

In a tandem mass spectrometry experiment, a peptide fragment with $$m/z = 1,268 is $$observed. If the possible amino acid masses are D (115), G (57), L (113), and M (131), and the order of the first two residues from N- to C-terminus is required, which pair is correct if the mass difference between the first two fragments is $$244$$?

Accepted Answer

N-terminal M, then L

Question 11

Which step in tandem mass spectrometry is most critical for distinguishing between two peptides that differ by a single amino acid?

Accepted Answer

Fragmentation of the selected ion and analysis of the resulting fragment ions.

Question 12

A scientist is analyzing a protein mixture using tandem mass spectrometry. Which of the following best describes how the technique can be used to identify a specific protein in the mixture?

Accepted Answer

By selecting and fragmenting ions unique to the protein of interest and analyzing the resulting fragments.

Question 13

Which of the following is a common misconception about tandem mass spectrometry?

Accepted Answer

It can only be used for purified proteins and not for mixtures.

Question 14

In tandem mass spectrometry, what is the role of the collision cell?

Accepted Answer

To fragment the selected precursor ion into smaller ions for further analysis.

Question 15

A peptide is analyzed by tandem mass spectrometry, and the following fragment ions are observed: $$m/z = 1,200$$, $$1,069$$, and $$956. If $$the mass differences correspond to amino acids D (115) and G (57), what is the likely sequence of the peptide from N- to C-terminus?

Accepted Answer

D-G

Tandem Mass Spectrometry in Protein Analysis

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