This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Techniques – Structure Analysis”.
1. Which of the following is used in PAGE to prevent the mixing of the sample with running buffer?
Explanation: For polyacrylamide gel electrophoresis (PAGE), the protein samples are prepared in a solution of sucrose or glycerol to provide density. This prevents the mixing of protein samples with the running buffer.
2. Proteins with greater charge density move faster in the PAGE.
Explanation: Charge density is the charge per unit mass of the protein molecule. The rate of movement of a protein through the gel matrix depends on its charge density, the more the charge density, the faster the protein will reach the electrode.
3. In gel electrophoresis, the globular proteins move slower than the fibrous proteins.
Explanation: In polyacrylamide gel electrophoresis, a sieve of molecular matrix is formed through which the proteins migrate depending on their shape and size. The compact globular proteins move faster than the elongated fibrous proteins.
4. When was the technique of two-dimensional gel electrophoresis developed?
Explanation: The technique of two-dimensional gel electrophoresis was developed in 1975 by Patrick O’Farrell at the University of California, San Francisco for fractionating proteins based on two different properties.
5. Which of the following amino acid absorbs the light of 280 nm?
Explanation: Spectrophotometry is a technique used to measure the protein content of a sample. Out of the 20 amino acids that make a protein, two amino acids – tyrosine and phenylalanine absorb light of 280 nm.
6. For a mass spectrometric analysis, the compounds are converted into ___________________
a) gaseous ions
b) soluble form
Explanation: For the mass spectrometric analysis of proteins, they are converted into positively-charged gaseous ions that are accelerated through a curved tube (under the influence of a magnetic field) to a negatively-charged plate.
7. In mass-spectrometry, proteins are separated base on their _____________________
c) m/z ratio
d) e/m ratio
Explanation: In mass spectrometry, proteins get separated based on their mass-to-charge (m/z) ratios. Smaller ions travel faster and strike the detector while the larger, heavier ions move slower.
8. Which is the main ingredient in the sample preparation of mass spectrometry?
Explanation: Trypsin is used in a mass spectrometric analysis to digest proteins. After protein digestion, there is a fractionation step using the liquid chromatographic procedures. After that the samples are ionized and made gaseous.
9. MALDI is a technique of ______________________
d) cell counting
Explanation: Matrix-assisted laser desorption ionization is a technique of sample ionization wherein the protein is applied as a part of crystalline matrix and irradiated by a laser pulse. As a result, the matrix is excited and the peptides are converted to a gaseous state.
10. Electrospray ionization is suited for proteins that are __________________
a) in matrix
b) in glycerol
c) in solution
d) of large size
Explanation: Electrospray ionization is an alternate procedure to Matrix-assisted laser desorption ionization, which is well suited for proteins in solution (the ones fractionated using liquid chromatography).
11. Which of the following techniques delivers the amino-acid sequence of a peptide?
a) Tandem MS
Explanation: Tandem MS (also termed MS/MS) is a two-step procedure that gives amino acid sequence of a polypeptide and hence a complete unmistakable identification of an unidentified protein.
12. In X-ray diffraction, the protein crystals are bombarded with ____________
a) UV rays
b) X rays
c) Gamma rays
d) Infrared rays
Explanation: In the technique of X-ray diffraction (also termed X-ray crystallography), the protein crystals are bombarded with X-rays in order to elucidate their crystalline structure and diffraction pattern.
13. Which was the first protein to have its structure determined using X-ray crystallography?
Explanation: Myoglobin was the first protein whose structure was determined using X-ray diffraction. Resolution obtainable by the method of X-ray crystallography depends on the spots being analyzed.
14. Synchrotrons generate _____________________
b) X rays
c) Infrared rays
Explanation: Synchrotron is a high energy cyclic-particle accelerator that produces X-rays as a by product. The highly focused X-ray beams generated are then used for creating diffraction patterns out of a protein crystal.
15. Electron cryomicroscopy is used mainly for _______________
a) soluble proteins
b) non-soluble proteins
Explanation: Electron cryomicroscopy (also termed CryoTEM or cryo-EM). This technique is used mainly for non-soluble proteins and organelles such as ribosomes. In this techniques sample are studied at cryogenic temperatures.
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