Q: Which equation correctly represents the calculation of the mass-to-charge ratio ($m/z$) for an ion in mass spectrometry?

$m/z = \frac{\text{mass of ion}}{\text{charge of ion}}$

Question 1

Which of the following best describes what is plotted on a mass spectrum in peptide mass spectrometry?

Accepted Answer

Relative abundance of ions versus their $m/z$ (mass-to-charge) ratio

Question 2

In mass spectrometry, which type of ion always contains the C-terminal amino acid residue and is read from right to left?

Accepted Answer

y ions

Question 3

A peptide is fragmented and analyzed by mass spectrometry. If the mass difference between two adjacent y-ion peaks is approximately 147 Da, which amino acid is most likely present between those peaks?

Accepted Answer

Phenylalanine ($F$), with a mass of approximately 147 Da

Question 4

Which statement about b and y ions in peptide mass spectrometry is correct?

Accepted Answer

b ions contain the N-terminal amino acid and are read from left to right; y ions contain the C-terminal amino acid and are read from right to left

Question 5

During peptide sequencing by mass spectrometry, which of the following is a major challenge when differentiating amino acids?

Accepted Answer

Distinguishing between leucine and isoleucine due to their identical masses

Question 6

Given a mass spectrum with y-ion peaks at $m/z$ values of 582, 1131, and 1283, and knowing the masses of relevant amino acids: Y (163), N (114), W (186), Q (146), S (87), F (147), L (113), and M (131), which amino acid is most likely the C-terminal residue of the peptide?

Accepted Answer

W (Tryptophan)

Question 7

If a peptide has a sequence ending in Lysine (K) and the mass spectrum shows a y-ion peak at $m/z = 147$, which amino acid is most likely present at the position before Lysine?

Accepted Answer

Phenylalanine ($F$)

Question 8

Which of the following best explains why y-ion peaks are often more prominent than b-ion peaks in a mass spectrum?

Accepted Answer

y ions are more stable and thus have higher intensity/abundance

Question 9

A peptide is fragmented and analyzed by mass spectrometry. If the mass difference between two adjacent b-ion peaks is 87 Da, which amino acid is most likely present between those peaks?

Accepted Answer

Serine ($S$), with a mass of approximately 87 Da

Question 10

Which equation correctly represents the calculation of the mass-to-charge ratio ($m/z$) for an ion in mass spectrometry?

Accepted Answer

$m/z = \frac{	ext{mass of ion}}{	ext{charge of ion}}$

Question 11

In a mass spectrum, which type of ion is most useful for determining the N-terminal sequence of a peptide?

Accepted Answer

b ions

Question 12

A peptide is analyzed by mass spectrometry and the following y-ion peaks are observed: $m/z = 186$, $m/z = 333$, $m/z = 480$. If the mass of tryptophan ($W$) is 186 Da and phenylalanine ($F$) is 147 Da, which sequence is most likely present at the C-terminus?

Accepted Answer

W-F

Question 13

Which of the following is a real-world application of peptide mass spectrometry in biochemistry?

Accepted Answer

Identifying protein sequences in disease biomarker discovery

Question 14

If a peptide mass spectrum shows a series of b-ion peaks with mass differences corresponding to the sequence S-Q-N, what are the approximate mass differences you would expect between the peaks?

Accepted Answer

$87$ Da (Serine), $146$ Da (Glutamine), $114$ Da (Asparagine)

Question 15

Which step is essential for determining the amino acid sequence of a peptide using mass spectrometry?

Accepted Answer

Analyzing the mass differences between adjacent ion peaks

Question 16

A mass spectrum of a peptide shows a prominent y-ion peak at $m/z = 163$. Which amino acid is most likely present at the C-terminal position?

Accepted Answer

Tyrosine ($Y$)

Question 17

Which of the following is NOT a reason why mass spectrometry is a powerful tool for peptide sequencing?

Accepted Answer

It can distinguish between amino acids with identical masses

Question 18

In mass spectrometry, which ion type is typically not detected but can be formed during peptide fragmentation?

Accepted Answer

a ions

Question 19

A peptide mass spectrum shows y-ion peaks at $m/z = 114$ and $m/z = 260$. If the mass of asparagine ($N$) is 114 Da and glutamine ($Q$) is 146 Da, which two amino acids are most likely present at the C-terminus?

Accepted Answer

N-Q

Mass Spectrometry in Protein and Peptide Sequencing

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