Gel Electrophoresis

Q1: In SDS-PAGE, the protein sample is first

A treated with a reducing agent and then with anionic detergent followed by fractionation by electrophoresis

B fractionated by electrophoresis then treated with an oxidizing agent followed by anionic detergent.

C treated with a oxidizing agent and then with anionic detergent followed by fractionation by electrophoresis

D none of the above

ANS:A - treated with a reducing agent and then with anionic detergent followed by fractionation by electrophoresis

No answer description is available.

Q2: Proteins can be visualized directly in gels by

A staining them with the dye

B using electron microscope only

C measuring their molecular weight

D none of these

ANS:A - staining them with the dye

The staining of the protein helps in the visualizing the protein in the form of the coloured band that also ease the identification of the protein and the isolation of the protein.

The staining of the protein can be done with the help of coomassie blu dye G250. This dye binds to the protein and thus help in the estimation of the protein. When DNA electrophoresis is been carried out the dye used is ethylene bromide.

Q3: In a gel filtration column

A smaller proteins enter the beads more readily

B large proteins elute first

C both (a) and (b)

D large proteins enter the beads more readily

ANS:C - both (a) and (b)

Small protein enters the gel beads easily whereas larger protein cannot enters the gel hence its elute easily.

Q4: The subunit molecular weight as well as the number of subunits in the quaternary structure can be determined by

A SDS-PAGE electrophoresis

B gel filtration chromatography

C combining information from (a)and (b)

D isoelectric focusing

ANS:C - combining information from (a)and (b)

The molecular weight of each subunit will be given by SDS-PAGE while the total number of subunits will be given by gel filtration chromatography.

Q5: Proteins are separated in an SDS-PAGE experiment on the basis of their

A positively charged side chains

B molecular weight

C negatively charged side chains

D different isoelectric points

ANS:B - molecular weight

Let say we have a approximately 10ug of protein running in a gel, what would look like if we load 1ug of protein on top of it?

Q6: Electrophoresis of histones and myoglobin under non-denaturing conditions (pH = 7.0) results in

A both proteins migrate to the anode

B histones migrate to the anode and myoglobin migrates to the cathode

C histones migrate to the cathode and myoglobin migrates to the anode

D both proteins migrate to the cathode

ANS:C - histones migrate to the cathode and myoglobin migrates to the anode

As compared to PI, Increased pH leads increased the H+ ion concentration, so it migrates towards -vely charged electrode (Cathode). When in decreased pH, increases the OH- ion concentrations, then it migrates towards +vely charged electrode (Anode).

Q7: In an SDS-PAGE

A proteins are denatured by the SDS

B proteins have the same charge-to-mass ratio

C smaller proteins migrate more rapidly through the gel

D all of the above

ANS:D - all of the above

SDS is an ionic detergent which imparts the negative charge to denatured proteins, generally, one SDS molecule binds with two amino acids hence all proteins in the sample have a negative charge so that the protein in the gel will migrate on the basis of charge to mass ratio. The proteins having less molecular weight will migrate faster in the gel as compare to the proteins having the higher mass to charge ratio.

Q8: In isoelectric focusing, proteins are separated on the basis of their

A relative content of positively charged residue only

B relative content of negatively charged residue only

C size

D relative content of positively and negatively charged residue

ANS:D - relative content of positively and negatively charged residue

Isoelectric focusing means the separation of the protein based on the isoelectric pH. Isoelectric pH is the pH at which the protein can exist at the neutral state.

For being neutral it should have both positive and negative charged residue. Thus isoelectric focusing is based on the relative content of positively and negatively charged residue.

Q9: In a native PAGE, proteins are separated on the basis of

A net negative charge

B net charge and size

C net positive charges size

D net positive charge

ANS:B - net charge and size

If two proteins have the same charges but differ in their molecular weight. Which of the protein will come out first in a native page?

Is it the smaller molecular weight or large molecular weight?



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