This set of Protein Engineering Problems focuses on “Structural Study – ESI-MS”.
1. Which of the following ionization techniques involves the production of ions by spraying a solution of the analyte into an electric field?
a) CI
b) MALDI
c) FAB
d) ESI
View Answer
Explanation: ESI is an ionization technique that involves the production of ions by spraying a solution of the analyte into an electric field. ESI is Electrospray Ionization. CI, MALDI, and FAB are the techniques that do not involve the production of ions by spraying a solution of the analyte into an electric field.
2. ESI is not a soft ionization technique.
a) True
b) False
View Answer
Explanation: The above statement is false. ESI is a soft ionization technique. In ESI the sample is present in the liquid form and ion are created by spraying a dilute solution of the analyte at atmospheric pressure from the tip of fine metallic capillary creating a mist of droplets.
3. ESI technique does not allow the analysis of large (underivatized) biomolecules, such as proteins and DNA.
a) True
b) False
View Answer
Explanation: The above statement is false. ESI technique does indeed allow the analysis of large (underivatized) biomolecules, such as proteins and DNA. It is a soft ionization technique and hence, shows this property.
4. What is the essential principle in ESI?
a) Solubilization
b) Nucleation
c) Sublimation
d) Nebulisation
View Answer
Explanation: Nebulisation is the essential principle in ESI. The electrospray creates very small droplets of the solvent-containing analyte. The essential principle in ESI is that a spray of charged liquid droplets is produced by atomization or nebulization.
5. The ions created in ESI are accelerated towards mass analyzer depending upon which criteria of ions?
a) Mass of the ion
b) Charge on the ion
c) Weight of the ion
d) Mass and charge of the ion
View Answer
Explanation: The ions created in ESI are accelerated towards mass analyzer depending upon mass and charge of the ion. It does not depend on the weight of the ion.
6. What is ESI is also known?
a) Standard Pressure Ionization (SPI)
b) High-Pressure Ionization (HPI)
c) Low-Pressure Ionization (LPI)
d) Atmospheric Pressure Ionization (API)
View Answer
Explanation: ESI is also known as Atmospheric Pressure Ionization (API). Ionization can occur at atmospheric pressure therefore; this method is also referred to as Atmospheric Pressure Ionization (API).
7. Which of the following ionization technique was able to overcome the propensity of the analyte fragmentation?
a) Electron ionization
b) FAB
c) Chemical ionization
d) ESI
View Answer
Explanation: ESI was the technique that was able to overcome the propensity of the analyte fragmentation. ESI-MS can also be used to precisely measure the molecular mass of the biologically important supramolecules like proteins.
8. Generally in ESI, very little residual energy is retained by the analyte, and no fragmentation occurs upon ionization.
a) False
b) True
View Answer
Explanation: The above statement is true. In ESI very little residual energy is retained by the analyte, and no fragmentation occurs upon ionization. Hence, it is called a soft ionization technique.
9. Who is the inventor of ESI-MS?
a) Benjamin Franklin
b) Franz H. Kemp
c) Michael Barber
d) John B. Fenn
View Answer
Explanation: John B. Fenn is the inventor of ESI-MS. He was awarded Noble prize in chemistry in 2002. Benjamin Franklin invented electricity. Franz H. Kemp invented an ionization technique known as MALDI. Michael Barber invented the FAB ionization technique.
10. Which of the following is not a component of ESI-MS mass spectrometry?
a) Electrospray ionizer
b) Detector
c) Mass analyzer
d) MALDI
View Answer
Explanation: MALDI is not a component of ESI-MS mass spectrometry. Electrospray ionizer, detector, and mass analyzer are components of ESI-MS mass spectrometry. MALDI is a component of MALDI-TOF mass spectrometry.
11. In ESI-MS vacuum should be maintained in which of the following components?
a) Detector only
b) Mass analyzer only
c) Ion source and mass analyzer
d) Mass analyzer and detector
View Answer
Explanation: In ESI-MS vacuum should be maintained in a mass analyzer and detector. This is done to reduce the collision between ions. A vacuum is not supposed to be present in the ion source.
12. In which of the following techniques the gaseous ions are subjected to two or more sequential stages of mass analysis according to the m/z ratio?
a) NMR spectroscopy
b) X-ray crystallography
c) Mass spectrometry
d) Tandem mass spectrometry
View Answer
Explanation: In tandem mass spectrometry the gaseous ions are subjected to two or more sequential stages of mass analysis according to the m/z ratio. This technique is also called as MS-MS. A particular ion from the spectrum is selected in the first MS and then it is fragmented in the collision box and selected in the second MS.
13. Which of the following is not an application of ESI-MS?
a) Protein identification and characterization
b) In the clinical laboratory
c) Studying non-covalent interactions
d) Studying covalent interactions
View Answer
Explanation: Studying covalent interactions is not an application of ESI-MS. ESI-MS finds application in protein identification and characterization, in the clinical laboratory, and the study of non-covalent interactions.
14. ESI-MS can successfully detect post-translational modifications and mutations.
a) False
b) True
View Answer
Explanation: The above statement is true. ESI-MS can successfully detect the post-translational modifications and the mutations because these processes lead to the change of proteins.
15. Sometimes intact charged protein generated by ESI is introduced into the mass analyzer and is subjected to gas-phase fragmentation. What is this type of approach called?
a) “Fragmentation” strategy of protein analysis
b) “Left-to-right” strategy of protein analysis
c) “Bottom-up” strategy of protein analysis
d) “Top-down” strategy of protein analysis
View Answer
Explanation: In the “top-down” strategy of protein analysis the charged protein generated by ESI is introduced into the mass analyzer and is subjected to gas-phase fragmentation. This approach starts with intact protein and leads to fragmented protein, therefore, it is known as the “top-down” strategy of protein analysis.
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