Proteins Structural Study Questions and Answers

This set of Protein Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Structural Study – MALDI-TOF”.

1. Which mass analyzer is most frequently used with MALDI?
a) Magnetic sector
b) Quadrupole
c) Ion trap
d) TOF
View Answer

Answer: d
Explanation: TOF is most commonly used with MALDI. It is best suited for MALDI as it can sort virtually all range of masses. The magnetic sector, Quadrupole, and ion trap are not used frequently with MALDI.

2. Which of the following ionization technique uses a short laser pulse to achieve ionization?
a) ESI
b) Chemical Ionization
c) FAB
d) MALDI
View Answer

Answer: d
Explanation: MALDI is the ionization technique that uses a short laser pulse to achieve ionization. ESI, Chemical Ionization, and FAB do not use a short laser pulse to achieve ionization. The target plate containing the sample is placed in a vacuum chamber with high voltage and short laser pulses are applied.

3. Sublimation occurs in which of the following ionization methods?
a) ESI
b) FAB
c) Chemical Ionization
d) MALDI
View Answer

Answer: d
Explanation: Sublimation occurs in MALDI. The laser energy applied on the target plate gets adsorbed by the matrix and is transferred to the analyte molecules which undergo rapid sublimation resulting in gas-phase ions. Whereas, sublimation does not occur in ESI, FAB, and chemical ionization.

4. Which of the following ionization method uses aromatic compounds and organic solvents to achieve ionization?
a) ESI
b) Chemical ionization
c) FAB
d) MALDI
View Answer

Answer: d
Explanation: The ionization method which uses aromatic compounds and organic solvents to achieve ionization is MALDI. ESI, chemical ionization, and FAB do not use aromatic compounds and organic solvents to achieve ionization.

5. In the TOF analyzer, all the ions are accelerated at the same velocity.
a) True
b) False
View Answer

Answer: b
Explanation: The above statement is false. In TOF, ions of lower mass are accelerated to higher velocities. Thus, in the TOF analyzer, all the ions are not accelerated at the same velocity.

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6. What is the relation of time of flight with the molecular mass of the ion in the TOF mass analyzer?
a) Time of flight is inversely proportional to the square root of the molecular mass of the ion
b) Time of flight is inversely proportional to the molecular mass of the ion
c) Time of flight is directly proportional to the molecular mass of the ion
d) Time of flight is directly proportional to the square root of the molecular mass of the ion
View Answer

Answer: d
Explanation: In TOF mass analyzer, the time of flight is directly proportional to the square root of the molecular mass of the ion. Hence, a charge having a small mass will have a smaller time of flight and an ion having a large mass would have a large time of flight.

7. Which of the following type of mass analyzer uses a magnetic field and cyclotron motion to trap ions?
a) Quadrupole
b) Orbitrap
c) TOF
d) Fourier transform ion cyclotron resonance
View Answer

Answer: d
Explanation: Fourier transform ion cyclotron resonance is a type of mass analyzer that uses a magnetic field and cyclotron motion to trap ions. Quadrupole, orbitrap, and TOF do not use magnetic field and cyclotron motion to trap ions.

8. In TOF, ions of lower mass are accelerated to lower velocities and reach the detector last.
a) True
b) False
View Answer

Answer: b
Explanation: The above statement is false. In TOF, ions of lower mass are accelerated to higher velocities and reach the detector first. Thus, ions are accelerated at different velocities depending on their mass-to-charge ratio.

9. If a charge has a mass of 3 kg and it is traveling at a speed of 10 m/s in-flight tube, then what will be it’s kinetic energy?
a) 300 J
b) 90 J
c) 100 J
d) 150 J
View Answer

Answer: d
Explanation: The kinetic energy of that charge would be 150 J.
Formula: K.E=\(\frac{1}{2}\)mv²
: K.E=\(\frac{1}{2}\) x 3 x 10²
K.E=150 J.

10. Which of the following cannot be used as a MALDI matrix compound?
a) α-Cyano-4-hydroxycinnamic acid
b) Sinapinic acid
c) 3-Hydroxypicolinic acid
d) 2,3-Dihydroxybenzoic acid
View Answer

Answer: d
Explanation: 2,3-Dihydroxybenzoic acid cannot be used as a MALDI matrix compound. α-Cyano-4-hydroxycinnamic acid, sinapinic acid, and 3-Hydroxypicolinic acid can be used as a MALDI matrix compound.

11. Which of the following is the correct equation of the time of flight?
a) t=(\(\frac{m}{2q}\))^0.5 x l
b) t=(\(\frac{m}{2q}\))^2.0 x l
c) t=(\(\frac{m}{2v^{\circ}}\))^2.0 x l
d) t=(\(\frac{m}{2v^{\circ}q}\))^0.5 x l
View Answer

Answer: d
Explanation: The correct equation for the time of flight is t=(\(\frac{m}{2v^{\circ}q}\))^0.5 x l.
Where, t is the time of flight,
m is the mass of ion,
q is the charge on ion,
v° is the accelerating potential.

12. Which of the following charge has the lowest m/z ratio?
Given data: q₁ has a charge +1 and mass of 800 Da,
q₂ has a charge +3 and mass of 3900 Da,
q₃ has a charge +2 and mass of 2970 Da,
q₄ has a charge +4 and a mass of 3480 Da.
a) q₄
b) q₃
c) q₂
d) q₁
View Answer

Answer: d
Explanation: The charge q₁ has the lowest m/z ratio.
Formula: \(\frac{m}{z}\)=\(\frac{mass \, of \, the \,ion}{charge \,on \,the \, ion}\)
For q₁\(\frac{m}{z}\)=\(\frac{800}{+1}\)=800
For q₂\(\frac{m}{z}\)=\(\frac{3900}{+3}\)=1300
For q₃\(\frac{m}{z}\)=\(\frac{2790}{+2}\)=1485
For q₄\(\frac{m}{z}\)=\(\frac{3480}{+4}\)=870
Hence, the m/z ratio of q₁ is lowest.

13. Which of the following provides higher resolution in MALDI-TOF?
a) Blocker
b) Channel
c) Transmitter
d) Reflector
View Answer

Answer: d
Explanation: Reflector provides higher resolution in MALDI-TOF. A reflector (or reflectron) is a type of ion mirror. It increases the overall path length for an ion and it corrects for minor variation in the energy spread of ions of the same mass.

14. Which of the following lasers can be used for laser radiation in MALDI?
a) Infrared lasers
b) Greenlight lasers
c) Red light lasers
d) Ultraviolet lasers
View Answer

Answer: d
Explanation: Ultraviolet lasers can be used for laser radiation in MALDI. Infrared lasers, green-light lasers, and red-light lasers cannot be used for laser radiation in MALDI. This laser radiation is done for a few nanoseconds’ duration. It is then absorbed by matrix molecules which causes rapid heating of that region.

15. Consider four ions q₁, q₂, q₃ and q₄. q₁ has a charge +3 and mass of 290 Da, q₂ has a charge +2, and mass of 290 Da, q₃ has a charge +3 and mass of 390 Da, and q₄ has a charge +2 and mass of 390 Da. Which one of these ions has a maximum m/z ratio?
a) q₁
b) q₂
c) q₃
d) q₄
View Answer

Answer: d
Explanation: The ion q₄ has a maximum m/z ratio.
Formula: \(\frac{m}{z}\)=\(\frac{mass \, of \, the \,ion}{charge \,on \,the \, ion}\)
For q₁\(\frac{m}{z}\)=\(\frac{290}{+3}\)=96.66
For q₂\(\frac{m}{z}\)=\(\frac{290}{+2}\)=145
For q₃\(\frac{m}{z}\)=\(\frac{390}{+3}\)=130
For q₄\(\frac{m}{z}\)=\(\frac{390}{+2}\)=195
Hence, the m/z ratio of q₄ is maximum.

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