This set of Protein Engineering Quiz focuses on “Methods of Protein Crystallization – 2”.
1. Macromolecular crystals are temperature sensitive.
a) False
b) True
View Answer
Explanation: The above statement is true. Macromolecular crystals are indeed temperature sensitive. They undergo extensive damage after prolonged exposure to radiation.
2. The extent of the diffraction pattern from a crystal is inversely correlated with its degree of internal order.
a) True
b) False
View Answer
Explanation: The above statement is false. The extent of the diffraction pattern from a crystal is directly correlated with its degree of internal order. The vaster the pattern or the higher the resolution to which it extends, the more structurally uniform are the molecules in the crystal and the more precise is their periodic arrangement.
3. Crystallization of proteins proceeds in two distinct steps. Which are these steps?
a) Solidification and crystallization
b) Crystallization and expansion
c) Growth and solidification
d) Nucleation and growth
View Answer
Explanation: Nucleation and growth are the two steps in which the crystallization of proteins proceeds. These steps are rather distinct but inseparable. Nucleation is the most difficult problem to address theoretically and experimentally.
4. Nucleation represents which order phase transition?
a) Zero-order
b) Third-order
c) Second-order
d) First-order
View Answer
Explanation: Nucleation represents a first-order phase transition by which molecules pass from a completely disordered state to an ordered one. Therefore, it is the most difficult problem to address theoretically and experimentally.
5. Which of the following is not a method for creating supersaturation?
a) Salting in
b) Salting out
c) Evaporation
d) Dilution
View Answer
Explanation: Dilution is not a method for creating supersaturation. It inhibits supersaturation. Salting in, salting out, and evaporation are methods for creating supersaturation.
6. Which of the following does not promote protein crystal formation?
a) Addition of organic solvents
b) Direct mixing of protein and precipitant solutions
c) Altering the temperature
d) Addition of a solubilizing agent
View Answer
Explanation: The addition of a solubilizing agent does not promote protein crystal formation. The addition of organic solvents, direct mixing of protein and precipitant solutions, and altering the temperature promotes protein crystal formation.
7. Find the odd one out.
a) Removal of water through a membrane
b) Altering the dielectric of the medium
c) Altering the pH
d) Addition of detergent
View Answer
Explanation: Removal of water through a membrane, Altering the dielectric of the medium, and Altering the pH promote the formation of crystals in protein crystallization. The addition of detergent does not promote protein crystallization. Hence, the addition of detergent is the odd one out.
8. Which of the following does not make the protein solution supersaturated?
a) Addition of salt
b) Change of pH
c) Addition of bridging ions
d) Addition of water
View Answer
Explanation: The addition of salt, change of pH, and addition of bridging ions make the protein solution supersaturated. The addition of water does not make the protein solution supersaturated.
9. In the sitting drop vapour diffusion method the protein drop is suspended from a coverslip over the reservoir.
a) True
b) False
View Answer
Explanation: The above statement is false. In the hanging drop vapour diffusion method the protein drop is suspended from a coverslip over the reservoir. Then, dehydration of drop occurs and nucleation and crystal growth take place.
10. In which of the following method, the protein drop is on the elevated platform?
a) Hanging-drop vapour diffusion method
b) Elevated-drop vapour diffusion method
c) Standing-drop vapour diffusion method
d) Sitting-drop vapour diffusion method
View Answer
Explanation: In the sitting-drop vapour diffusion method the protein drop is on the elevated platform. In the hanging-drop vapour diffusion method, a droplet is suspended on the inner side of the cover.
11. Which of the following method takes advantage of a semi-permeable membrane for protein crystallization?
a) Vapour diffusion
b) Micro-batch crystallization
c) Free-interface diffusion
d) Microdialysis
View Answer
Explanation: The microdialysis method of protein crystallization takes advantage of a semi-permeable membrane for protein crystallization.
12. Which of the following method utilizes free diffusion between a concentrated protein solution and a precipitant solution?
a) Micro-batch crystallization
b) Vapour diffusion
c) Microdialysis
d) Free-interface diffusion
View Answer
Explanation: The free-interface diffusion method utilizes free diffusion between a concentrated protein solution and a precipitant solution. This is done to attain the conditions of protein supersaturation, which is required for nucleation and subsequent growth.
13. In which of the following method, the droplet must be covered with paraffin oil to prevent evaporation?
a) Microdialysis
b) Free-interface diffusion
c) Vapour diffusion
d) Micro-batch crystallization
View Answer
Explanation: In micro-batch crystallization, the droplet must be covered with paraffin oil to prevent evaporation. This is done because a very small volume of the droplet is used.
14. Which of the following method uses different conditions for nucleation and growth to achieve improved crystal quality?
a) Vapour diffusion
b) Microdialysis
c) Free-interface diffusion
d) Micro-batch crystallization
View Answer
Explanation: The Micro-batch crystallization method uses different conditions for nucleation and growth to achieve improved crystal quality. It involves the simple combination of protein with precipitants, buffers, etc. generally without any subsequent concentration steps.
15. Which of the following is a correct feature for the free-interface diffusion method of protein crystallization?
a) Only one layer of precipitant solution
b) Only one layer of protein solution
c) The upper layer of a precipitant solution and lower layer of protein solution
d) The upper layer of protein solution and lower layer of precipitant solution
View Answer
Explanation: The upper layer of protein solution and lower layer of precipitant solution is a correct feature for the free-interface diffusion method of protein crystallization. These two layers are allowed to diffuse to equilibrium. The transient protein supersaturation near the interface induces the formation of nuclei.
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