This set of Protein Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Structural Study – NMR Spectroscopy”.
1. Which of the following is a technique for the determination of the three-dimensional structure of a protein?
a) Gas chromatography
b) Mass spectroscopy
c) Radiotherapy
d) NMR spectroscopy
View Answer
Explanation: NMR spectroscopy is a technique for the determination of the three-dimensional structure of a protein. NMR spectroscopy stands for Nuclear Magnetic Resonance spectroscopy. Gas chromatography, mass spectroscopy, and radiotherapy cannot be used for the determination of the three-dimensional structure of a protein.
2. Which of the following is a spectroscopic technique used to observe local magnetic fields around atomic nuclei?
a) Optical spectroscopy
b) Atomic spectroscopy
c) Massspectroscopy
d) NMR spectroscopy
View Answer
Explanation: NMR spectroscopy is a spectroscopic technique that is used to observe local magnetic fields around atomic nuclei. In this technique, the sample is placed in a magnetic field and the NMR signal is produced by the excitation of the nuclei sample with radio waves into nuclear magnetic resonance, which is then detected with sensitive radio receivers.
3. Which of the following is the definitive method to identify monomolecular organic compounds?
a) Mass spectroscopy
b) Infrared spectroscopy
c) X – ray crystallography
d) NMR spectroscopy
View Answer
Explanation: NMR spectroscopy is the definitive method to identify monomolecular organic compounds. This is because the intramolecular magnetic fields around an atom are unique or highly characteristic to individual compounds.
4. Which of the following isotope is NMR inactive?
a) 1H
b) 13C
c) 15N
d) 12C
View Answer
Explanation: 1H, 13C, and 15N are the isotopes that are NMR active. 12C is an NMR inactive isotope. Only certain isotopes have a magnetic spin; hence they are called NMR active isotopes.
5. Which of the following isotope is NMR inactive?
a) 1H
b) 13C
c) 31P
d) 16O
View Answer
Explanation: 1H, 13C, and 31P are the isotopes that are NMR active. 16O is an NMR inactive isotope. The isotopes that have a magnetic spin are termed as NMR active isotopes, and those that do not have a magnetic spin are termed as NMR inactive isotopes.
6. Which of the following isotopes has a magnetic spin?
a) 16O
b) 12C
c) 14N
d) 31P
View Answer
Explanation: 12C, 16O, and 14N are the isotopes that do not have a magnetic spin; hence, they are also called as NMR inactive isotopes. 31P has a magnetic spin hence, it is called NMR active isotope.
7. Which of the following isotopes has a magnetic spin?
a) 12C
b) 16O
c) 14N
d) 15N
View Answer
Explanation: 12C, 16O, and 14N are the isotopes that do not have a magnetic spin; hence, they are also called as NMR inactive isotopes. 15N has a magnetic spin hence, it is called NMR active isotope.
8. The chemical shift of an atomic nucleus depends on its molecular environment and is different for each atom in a protein molecule.
a) False
b) True
View Answer
Explanation: The above statement is true. The chemical shift of an atomic nucleus depends on its molecular environment and is different for each atom in a protein molecule. The chemical shift is the same for two magnetically equivalent atoms.
9. Three-dimensional structural information is obtained primarily from ‘through space’ NMR experiments involving the ‘nuclear Overhauser effect (NOE)’.
a) False
b) True
View Answer
Explanation: The above statement is true. Three-dimensional structural information is obtained primarily from ‘through space’ NMR experiments involving the ‘nuclear Overhauser effect (NOE)’. The NOE is a nuclear relaxation effect.
10. NMR spectroscopy cannot be used to study which of the following?
a) Interaction of protein with other molecules
b) Dynamic motion within proteins
c) Protein folding
d) Protein sequence
View Answer
Explanation: NMR spectroscopy cannot be used to study the protein sequence. Interaction of protein with other molecules, dynamic motion within proteins, and protein folding can be studied with the help of NMR spectroscopy.
11. Which of the following is not a limitation of NMR spectroscopy?
a) Mostly used for small proteins (< 30 kDa)
b) Can only be used for proteins that are stable in solution
c) Problem arises with high frequencies (1000 MHz)
d) Cannot detect dynamic motion within proteins
View Answer
Explanation: NMR spectroscopy is mostly used for small proteins i.e. for proteins that have a molecular weight less than 30 kDa. NMR spectroscopy can only be used for proteins that are stable in solution. Problem arises with the use of high frequencies (1000 MHz) in NMR spectroscopy. NMR spectroscopy can detect dynamic motion within proteins.
12. Which of the following isotopes have a magnetic spin?
a) 2He and 13C
b) 2He and 12C
c) 1H and 12C
d) 1H and 13C
View Answer
Explanation: 2He and 12C are the isotopes that are NMR inactive i.e. they do not have a magnetic spin. 1H and 13C are the isotopes that are NMR active i.e. they have a magnetic spin.
13. Which of the following isotopes does not have a magnetic spin?
a) 1H and 15N
b) 1H and 16O
c) 12C and 31P
d) 12C and 16O
View Answer
Explanation: 1H, 15N, and 31P are among the few isotopes that have a magnetic spin, and hence, they are called NMR active. 12C and 16O are NMR inactive and they don’t have a magnetic spin.
14. Protein samples are now routinely enriched with which of the following isotopes to simplify the NMR data?
a) 1H and 31P
b) 31P and 15N
c) 1H and 15N
d) 13C and 15N
View Answer
Explanation: 1H and 31P are not used in the enrichment of proteins. 13C and 15N are NMR active isotope and have a magnetic spin. Hence, protein samples are now routinely enriched with 13C and 15N isotopes to simplify the NMR data.
15. What are the different frequencies obtained as NMR peaks called?
a) Chemical peaks
b) Biological shifts
c) Physical shifts
d) Chemical shifts
View Answer
Explanation: In NMR spectroscopy, when the samples are irradiated with a pulse of radiofrequency electromagnetic radiation, NMR active nuclei will resonate at characteristic frequencies. The different frequencies obtained as NMR peaks (relative to a reference signal) are called as chemical shifts.
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