This set of Protein Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Methods of Protein Crystallization – 1”.
1. Which of the following is the process of the formation of a protein crystal?
a) Protein solubilization
b) Protein solidification
c) Protein concentration
d) Protein crystallization
View Answer
Explanation: Protein crystallization is the process of formation of a protein crystal. Like many other types of molecules, proteins can be prompted to form crystals. It is done for structural studies of protein.
2. Proteins can be prompted to form crystals when the solution in which they are dissolved becomes unsaturated.
a) True
b) False
View Answer
Explanation: The above statement is false. Proteins can be prompted to form crystals when the solution in which they are dissolved becomes supersaturated. Under these conditions, individual protein molecules can pack in a repeating array, held together by non-covalent interactions.
3. Protein crystallization is predominantly carried out in the water.
a) False
b) True
View Answer
Explanation: The above statement is true. Proteins are biological macromolecules and function in an aqueous environment. Thus, protein crystallization is predominantly carried out in the water.
4. Most proteins are soluble at physiological conditions, but as the concentration of solutes (ions, precipitants, etc.) rises, the protein becomes less soluble. Thus, it crystallizes or precipitates. What is this phenomenon known as?
a) Resolubilization
b) Coagulation
c) Salting in
d) Salting out
View Answer
Explanation: When the concentration of solutes (ions, precipitants, etc.) rises, the protein becomes less soluble and forms a precipitate. This phenomenon is known as salting out.
5. At very low solute concentration, proteins also become less soluble and form crystals. What is this phenomenon known as?
a) Salt precipitation
b) Salt minimization
c) Salting out
d) Salting in
View Answer
Explanation: At very low solute concentration, proteins also become less soluble, and form crystals. This happens because some solutes are necessary for the protein to remain in solution. This phenomenon is known as salting in.
6. Protein crystallization is inherently difficult because of the fragile nature of protein crystals.
a) False
b) True
View Answer
Explanation: The above statement is true. Protein crystallization is indeed inherently difficult because of the fragile nature of protein crystals. Proteins have irregularly shaped surfaces which results in the formation of large channels within any protein crystal.
7. Which of the following parameters does not influence the likelihood of protein crystallization?
a) Concentration of protein
b) Temperature
c) pH
d) Volume of sample
View Answer
Explanation: Concentration of protein, temperature, and pH are the parameters that influence the likelihood of protein crystallization. The volume of the sample does not influence the likelihood of protein crystallization.
8. Find the odd one out?
a) Hanging drop vapour diffusion method
b) Sitting drop vapour diffusion method
c) Micro-dialysis method
d) Standing drop vapour diffusion method
View Answer
Explanation: Hanging drop vapour diffusion method, sitting drop vapour diffusion method, and microdialysis method are methods of protein crystallization. Whereas, standing drop vapour diffusion method is not a method of protein crystallization.
9. Which of the following is not used to promote the formation of proteins crystals?
a) PEG
b) Ammonium sulfate
c) Tris-HCL
d) Ammonium nitrate
View Answer
Explanation: PEG and ammonium sulfate are precipitants and hence, promote the formation of proteins crystals. Tris-HCL is a buffer and is necessary to maintain pH. Ammonium nitrate is not used to promote the formation of proteins crystals.
10. Which of the following is not required for protein crystallization?
a) Buffer
b) Additive
c) Precipitants
d) Denaturants
View Answer
Explanation: Buffers are required to maintain the pH. Additives and precipitants are also required to promote protein crystallization. Denaturants are not required for protein crystallization.
11. Which is the most common method of protein crystallization?
a) Free-interface diffusion
b) Microdialysis
c) Micro-batch
d) Vapour diffusion
View Answer
Explanation: Vapour diffusion is the most common method of protein crystallization. Free-interface diffusion, microdialysis, and micro-batch are not so common methods of protein crystallization.
12. In the vapour diffusion method of protein crystallization, a droplet is allowed to equilibrate with a larger reservoir containing buffers and precipitants. Which of the following is not a constituent of this droplet?
a) Purified protein
b) Buffer
c) Precipitant
d) Denatured DNA
View Answer
Explanation: Denatured DNA is not a constituent of the droplet which is allowed to equilibrate with a larger reservoir containing buffers and precipitants. Purified protein, buffer, and precipitant are all constituents of the droplet.
13. Initially, the droplet of protein solution contains comparatively high precipitant and protein concentrations.
a) True
b) False
View Answer
Explanation: Initially, the droplet of protein solution contains comparatively low precipitant and protein concentrations, but as the drop and reservoir equilibrate, the concentration of protein and precipitant increase in the drop.
14. Which of the following is not related to vapour diffusion method of protein crystallization?
a) High concentration in reservoir
b) The Most commonly used method
c) Gentle and gradual change in concentration
d) An abrupt change in concentration
View Answer
Explanation: Abrupt change in concentration is not related to vapour diffusion method of protein crystallization. Vapour diffusion is the most commonly used method of protein crystallization. In this method, the reservoir contains higher concentrations of solutes. There is a gentle and gradual change in concentration of the droplet in this method.
15. Macromolecular crystals are composed of approximately how much percent solvent on average?
a) Zero percent
b) 10 percent
c) 95 percent
d) 50 percent
View Answer
Explanation: Macromolecular crystals are composed of approximately 50 percent solvent on average. It can also vary from 25 to 90 percent depending on the particular macromolecule. Protein occupies the remaining volume.
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