Question 1

Which property is primarily used by mass spectrometry to identify and quantify molecules?

Accepted Answer

Mass-to-charge ratio ($$\frac{m}{z})$$

Question 2

In mass spectrometry, why is the charge ($$z) of an $$ion often assumed to be 1 when calculating $$\frac{m}{z}$$?

Accepted Answer

Because most ions formed have a single positive charge

Question 3

During the ionization step in mass spectrometry, what is the primary purpose of bombarding the sample with electrons?

Accepted Answer

To fragment the sample into smaller ions

Question 4

Which of the following best describes the path of ions in a mass spectrometer after they are accelerated by an electric field?

Accepted Answer

They are deflected by a magnetic field based on their $$\frac{m}{z}$$ ratio

Question 5

If a peptide bond between two Gly residues does not break during mass spectrometry, which amino acid would be identified in place of the two glycines?

Accepted Answer

Lys

Question 6

A peptide bond between Ser and Val does not break during mass spectrometry. Which amino acid would be identified?

Accepted Answer

Tyr

Question 7

Which step in mass spectrometry is responsible for separating ions based on their mass-to-charge ratio ($$\frac{m}{z}$$)?

Accepted Answer

Acceleration and deflection in a magnetic field

Question 8

Why do ions with a larger $$\frac{m}{z}$$ ratio experience less deflection in a magnetic field during mass spectrometry?

Accepted Answer

Because they are heavier and less affected by the magnetic field

Question 9

A mass spectrometer detects a peak at $$m/z = 186.21. $$Which amino acid is most likely responsible for this peak?

Accepted Answer

Tyrosine

Question 10

Which of the following is NOT a typical step in the operation of a mass spectrometer?

Accepted Answer

Covalent modification of the sample

Question 11

A peptide is analyzed by mass spectrometry, and a fragment with $$m/z = 75.07 is $$detected. Which amino acid does this most likely correspond to?

Accepted Answer

Glycine

Question 12

If a peptide bond does not break between two residues, how does this affect the mass spectrum?

Accepted Answer

It results in a peak corresponding to the combined mass of both residues

Question 13

Which of the following best explains why mass spectrometry is useful for protein sequencing?

Accepted Answer

It can determine the mass of peptide fragments, allowing deduction of amino acid sequence

Question 14

In a mass spectrometry experiment, which factor would most likely cause two ions to have the same $$\frac{m}{z}$$ value?

Accepted Answer

They have the same mass and charge

Question 15

A mass spectrometer is set to detect ions with $$z = 2. If a $$fragment has a mass of 200 Da, what $$m/z$$ value will be detected?

Accepted Answer

$$100$$

Question 16

Which of the following scenarios would most likely result in a misidentification of an amino acid in mass spectrometry?

Accepted Answer

Failure to break a peptide bond between two residues

Question 17

If a peptide fragment is detected with a mass of 105.09 Da, which amino acid is most likely present?

Accepted Answer

Serine

Question 18

Which of the following is a limitation of mass spectrometry in protein analysis?

Accepted Answer

Not all peptide bonds break, leading to ambiguous fragment identification

Question 19

A mass spectrometer separates ions based on their $$\frac{m}{z}$$ ratio. If two fragments have the same mass but different charges, how will their $$\frac{m}{z}$$ values compare?

Accepted Answer

The fragment with the higher charge will have a lower $$\frac{m}{z}$$ value

Question 20

Which of the following best describes the role of the detector in a mass spectrometer?

Accepted Answer

It measures the abundance of ions at each $$\frac{m}{z}$$ value

Mass Spectrometry in Protein and Amino Acid Analysis

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