Cheryl is performing SDS-PAGE gel electrophoresis but she forgets to heat her samples with SDS. Which of the following occurs as a result of Cheryl's mistake?

A. Proteins separate by charge instead of by molecular mass B. Polypeptides do not unfold and thus migrate at slower rates through the gel C. Proteins do not migrate through the gel D. All of the above may occur as a result of Cheryl's mistake

Answer: B. Polypeptides do not unfold and thus migrate at slower rates through the gel.

Explanation:

SDS-PAGE is a gel electrophoresis used to separate charged molecules by their molecular masses in an electric field. To do this, it uses SDS (sodium dodecyl sulfat) to isolate proteins.

SDS is an amphipathic surfactant which covers the intrinsic charge of the proteins. It denatures proteins by binding to the chain and coating the protein with surfactant molecules. So it disrupts the tertiary structure of proteins, and this brings the folded proteins down to linear molecules which makes them have similar charge-to-mass ratios.

Proteins treated with SDS will have a negative charge, and during the application of a constant electric field, the protein migrate towards the anode (positive charge), each with a different speed according to the mass.

Without SDS, proteins do not unfold and wont be uniformly negatively charged. This means migrate slower.