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Multiple Choice Questions on Protein Purification Methods

1. For the study of a protein in detail, an effort is usually made to first:
a) conjugate the protein to a known molecule.
b) determine its amino acid composition.
c) determine its amino acid sequence.
d) determine its molecular weight.
e) purify the protein.

2. In a mixture of the five proteins listed below, which should elute second in size-exclusion (gel- filtration) chromatography?
gel filtration chromatography
a) cytochrome c Mr = 13,000
b) immunoglobulin G Mr = 145,000
c) ribonuclease A Mr = 13,700
d) RNA polymerase Mr = 450,000
e) serum albumin Mr = 68,500

3.By adding SDS (sodium dodecyl sulfate) during the electrophoresis of proteins, it is possible to:
a) determine a protein’s isoelectric point.
b) determine an enzyme’s specific activity.
c) determine the amino acid composition of the protein.
d) preserve a protein’s native structure and biological activity.
e) separate proteins exclusively on the basis of molecular weight.


4. To determine the isoelectric point of a protein, first establish that a gel:
a) contains a denaturing detergent that can distribute uniform negative charges over the protein’s surface.
b) exhibits a stable pH gradient when ampholytes become distributed in an electric field.
c) is washed with an antibody specific to the protein of interest.
d) neutralizes all ionic groups on a protein by titrating them with strong bases.
e) relates the unknown protein to a series of protein markers with known molecular weights, Mr.

5. The first step in two-dimensional gel electrophoresis generates a series of protein bands by isoelectric focusing. In a second step, a strip of this gel is turned 90 degrees, placed on another gel containing SDS, and electric current is again applied. In this second step:
a) proteins with similar isoelectric points become further separated according to their molecular weights.
b) the individual bands become stained so that the isoelectric focus pattern can be visualized.
c) the individual bands become visualized by interacting with protein-specific antibodies in the second gel.
d) the individual bands undergo a second, more intense isoelectric focusing.
e) the proteins in the bands separate more completely because the second electric current is in the opposite polarity to the first current.

6. The term specific activity differs from the term activity in that specific activity:
a) is measured only under optimal conditions.
b) is the activity (enzyme units) in a milligram of protein.
c) is the activity (enzyme units) of a specific protein.
d) refers only to a purified protein.
e) refers to proteins other than enzymes.

7. In isoelectric focusing, separation of proteins are based on
a) relative content of positively charged groups
b) relative content of negatively charged groups
c) both a and b
d) pH
e) None of these

8. Which of the following statement is incorrect
a) In affinity chromatography, lectins are used to purify a glycoprotein
b) The separation in gel filtration chromatography is based on size, shape and net charge of the protein
c) In Ion exchange chromatography, the bound proteins are eluted using NaCl solution
d) In affinity chromatography, the binding of a protein to a ligand is by specific non-covalent interactions
e) all of these
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Answers
1. e) purify the protein.
2. b) immunoglobulin G Mr = 145,000
3. e) separate proteins exclusively on the basis of molecular weight.
4. b) exhibits a stable pH gradient when ampholytes become distributed in an electric field.
5. a) proteins with similar isoelectric points become further separated according to their molecular weights.
6. b) is the activity (enzyme units) in a milligram of protein.
7. c) both a and b
8. b) The separation in gel filtration chromatography is based on size, shape and net charge of the protein
Reference: Lehninger Principles of Biochemistry Fourth Edition (Nelson and Cox)

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