Question

Select the true statements about SDS‑PAGE, a method of separating proteins. Assume that SDS‑PAGE is performed under reducing conditions. A) Proteins are visualized using a dye that binds to the gel matrix, but not to proteins. B) Sodium dodecyl sulfate binds proteins, resulting in protein‑SDS complexes that are similar in size. C) Protein‑SDS complexes migrate toward the positive electrode. D) SDS‑PAGE utilizes agarose gel to separate proteins. E) Smaller proteins migrate faster through the polyacrylamide gel. F) A protein binds roughly 1.4 times its mass of SDS, resulting in a large overall negative charge.

Answer 1

The true statements about SDS-PAGE are that SDS binds to proteins leading them to migrate towards the positive electrode (B, C), and smaller proteins migrate faster through the polyacrylamide gel (E). The method does not use agarose gel (D is false) and proteins are visualized with dyes binding to proteins, not the gel matrix (A is false). Furthermore, while proteins have a large negative charge due to SDS binding, the exact mass ratio may vary (F is misleading).

Step-by-step explanation:

Selecting the true statements about SDS-PAGE, a method of separating proteins under reducing conditions, several points are to be considered. Sodium dodecyl sulfate (SDS) is a detergent that binds to proteins, resulting in protein-SDS complexes that have a uniformly negative charge, which causes these complexes to migrate towards the positive electrode during the electrophoresis process. The SDS-PAGE technique utilizes a polyacrylamide gel, not agarose, to separate proteins. Smaller proteins typically migrate faster through the polyacrylamide gel due to the size-dependent nature of this electrophoretic technique. Lastly, proteins bind SDS in a ratio that results in a significant overall negative charge, often described with the rule of thumb that a protein binds roughly 1.4 times its mass of SDS.

Referring to the provided statements:

• (B) is true as SDS binds to proteins, resulting in complexes that have a similar size-to-charge ratio.
• (C) is true because protein-SDS complexes move toward the positive electrode during electrophoresis.
• (E) is true as smaller proteins indeed migrate faster through the polyacrylamide gel.

Conversely:

• (A) is false because proteins are typically visualized using dyes that specifically bind to proteins, not the gel matrix.
• (D) is false as SDS-PAGE uses polyacrylamide gel instead of agarose gel for protein separation.
• (F) is somewhat misleading as although proteins do bind a significant amount of SDS, stating that proteins bind exactly 1.4 times their mass in SDS may not be accurate for all proteins.

Answer 2

The correct statements are options C, E and F.

Step-by-step explanation:

The SDS-PAGE refers to a broadly utilized technique for distinguishing proteins. The SDS or the sodium dodecyl sulfate refers to an ionic detergent. The SDS-protein complexes possess negative charge with identical charge to mass ratio such that when the proteins are run on the gel they are distinguished on the basis of their size.

As the SDS entices a negative charge to the proteins, the migration of the proteins takes place towards the positive electrode. The migration of protein takes place on the basis of the size. Thus, smaller proteins seem to migrate quickly via the gel in comparison to the bigger proteins. The binding of the protein takes place with about 1.4 times its mass of SDS resulting in the formation of a large overall negative charge.