Two distinct bands appear in a single lane at the completion of an SDS-PAGE analysis of an unknown protein. Select one: a. These bands represent two subunits of a homodimer. b. Each band represents a different sized subunit of a multimeric protein. c. Each band represents a protein subunit with different charge to mass ratio. d. These bands represent two subunits of a heterodimer. e. These bands represent two separate subunits of identical size.

b. Each band represents a different-sized subunit of a multimeric protein.

Explanation:

SDS-PAGE analysis allows the separation and discrimination of proteins according to their molecular weight. The technique separates proteins in an electromagnetic field.

The SDS-PAGE technique makes proteins move in solid support -gel- by the action of the electric field. The distance reached by each protein is proportional to their molecular weight. The protein separation from a mixture results in bands that reflect their size.

SDS is a detergent that denaturalizes the protein and sets a relation charge size, such as that the motion of the protein in the gel is proportional to its weight. The bigger the protein is, the stronger interaction with the polyacrylamide gel there will be.  The speed of displacement in the electromagnetic field is inversely proportional to the protein size.

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