This set of Cell Biology Multiple Choice Questions & Answers (MCQs) focuses on “Protein Techniques”.
1. Purification of a protein can be measured as an increase in _____________
b) pH value
c) specific activity
Explanation: Purification of a protein can be measured as an increase in the specific activity of the protein. Specific activity is the ratio of amount of that protein to the total amount of protein in that sample.
2. Total nitrogen measurement can be used to measure ____________
a) pH drift
b) total protein
c) specific enzyme
Explanation: Proteins are made up of amino acids which have a carbon and a nitrogen end. The nitrogen molecule takes part in the peptide bond formation thus the nitrogen content is an intrinsic property of protein. Therefore nitrogen count can help in estimation of protein content in a sample.
3. Protein’s solubility depends on the relative balance between protein-solvent and protein-protein interactions.
Explanation: Every protein has a different solubility and it is a relative balance between the protein-solvent and protein-protein interactions. The former causes the protein to remain in solution, and the latter causes it to aggregate.
4. Which of the following can be used for selective precipitation of proteins?
c) ammonium sulfate
d) sodium acetate
Explanation: Ammonium sulfate is commonly used for selective precipitation of proteins. It is highly soluble in water and has high ionic strength. Purification is achieved by gradually adding the salt solution to crude protein extract.
5. In the liquid column chromatography, there are two phases namely ___________________ and ____________________
a) mobile, immobile
b) liquid, gel
c) viscous, non-viscous
d) flammable, inflammable
Explanation: In the liquid chromatography, there are two columns namely the mobile phase and the immobile phase. The proteins bind to sites on the immobile (stationary phase) and pass through the column based on their affinity.
6. Which of the following uses non-compressible matrix and high pressure?
Explanation: High performance liquid chromatography (HPLC) uses long, narrow columns in while the mobile phase is forced through the non-compressible stationary phase under high pressure.
7. When the pH of a protein is lowered _________________________
a) temperature decreases
b) negatively-charged groups neutralize
c) positively-charged groups neutralize
d) positively-charged groups decrease
Explanation: When the pH (potential hydrogen) of a protein is lowered, the negatively charged groups become neutralized whereas the positively-charged groups become abundant. The opposite occurs when the pH increases.
8. A protein is neutral at the isoelectric point.
Explanation: Isoelectric point is the pH value at which the negative charges and the positive charges are equal in a protein, and the protein is neutral. Usually, the isoelectric point of proteins is below 7.
9. Which of the following is used as an ion-exchanger resin?
Explanation: Ion-exchange chromatography uses ionic bonding of proteins to an inert matrix material such as cellulose. Two types of cellulose resins commonly used are diethyl-aminoethyl (DEAE) cellulose and carboxymethyl (CM) cellulose.
10. In ion-exchange chromatography, proteins bound to the resin can be displaced by increasing the _____________________
a) strength of ionic buffer
b) size of sample
c) column volume
d) column width
Explanation: In ion-exchange chromatography, the proteins bind reversibly to the inert resin through ionic bonds. To displace and eventually elute the bound proteins the ionic strength of buffer can be increased.
11. Gel-filtration chromatography separates proteins based on their ___________________
d) effective size
Explanation: Gel-filtration chromatography separates the proteins based on their effective size (hydrodynamic radius). The column material consists of cross-linked polysaccharides like agarose and dextrans.
12. In gel-filtration chromatography, the proteins ______________________
a) bind to the column
b) diffuse through the column
Explanation: The gel used for this technique used small beads that are tightly packed in the column. This causes a small void to form between the beads. The proteins that are larger than the voids pass through or diffuse through the gel.
13. Proteins interacting with specific substances can be separated using ___________________
a) ion-exchange chromatography
b) paper chromatography
c) affinity chromatography
d) gel-filtration chromatography
Explanation: The proteins participating in interactions such as ligand-ligand, enzyme-substrate etc. can be purified using the affinity chromatography. In this technique, an interacting molecule is covalently attached to the inert matrix.
14. The yeast two-hybrid system is used for studying ________________________
a) protein-protein interactions
b) pressure changes
c) molecular size
d) differentiation pattern
Explanation: The yeast two-hybrid system is used for studying protein-protein interactions. It was developed in 1989 by Stanley Fields and Ok-kyu Song at the State University of New York in Stony Brook.
15. Polyacrylamide gel electrophoresis uses ___________________ to separate proteins.
a) pressure difference
b) temperature difference
c) electric field
d) magnetic field
Explanation: Polyacrylamide gel electrophoresis (PAGE) is a powerful technique that uses electric field to separate out proteins in a matrix. Small organic molecules of acrylamide are cross-linked to form a molecular sieve through which the proteins travel.
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