Question

A protein sample has been treated differently before being loaded onto the gel for SDS-PAGE. The first aliquot of the sample is treated with SDS. The second aliquot of the sample is treated with SDS and a reducing agent. If there is no difference in the number of bands when comparing the results of the two experiments, the results most likely indicate...

Select one:
a. experimental contamination
b. that the proteins' non-covalent forces were additively stronger than the force of the disulfide bond(s)
c. that the protein was not denatured fully
d. that the protein being studied contain disulfide bonds in its quaternary structure
e. that the protein being studied does not contain disulfide bonds in its quaternary structure

Answer 1

e. that the protein being studied does not contain disulfide bonds in its Quaternary structure

Step-by-step explanation:

SDS-PAGE is an analytical method that is used to separate charged molecules such as proteins.

In the above experiment, the protein sample was treated with SDS. SDS disrupts the hydrogen bonding in proteins making it linear in conformation.

It also provides a negative charge enabling the proteins be separated according to size only.

On the other hand, reducing agents serve to break disulfide bonding in the proteins.

Therefore, the protein being studied in the experiment lacked disulfide bonds hence there was no difference in bands.

Answer 2

The correct answer is option e. "that the protein being studied does not contain disulfide bonds in its quaternary structure".

Step-by-step explanation:

Reducing agents, such as ß-mercaptoethanol (BME) or dithiothritol (DTT), are elements or compounds that break down disulfide bonds. These agents reduce the disulfide bonds and prevent the oxidation of the thiol groups of the cysteine residues that form the disulfide bonds. If one protein that was not treated with a reducing agent have the same electrophoretic behavior than a protein that was treated with a reducing agent in a SDS-PAGE experiment, then the results most likely indicate that the protein being studied does not contain disulfide bonds in its quaternary structure.