A protein ladder position: 150 kDa at 1.0 cm, 50 kDa at 4.0 cm, 25 kDa at 6.0 cm. An unknown band migrates to 3.0 cm. Using linear interpolation on log10(MW) between 150 kDa and 50 kDa, estimate the molecular weight of the unknown. Show calculations.

• A. Approximately 50 kDa because the gel distances always convert to the mid-range marker by default and the unknown falls within that general band for routine reporting purposes.
• B. Approximately 150 kDa because the protein is likely aggregated on the gel reducing migration and giving an appearance near the high molecular weight marker.
• C. Approximately 72 kDa (via log-linear interpolation between 150 kDa and 50 kDa markers).
• D. Approximately 25 kDa since the unknown migrated closer to the 25 kDa marker and therefore should be reported as the nearest lower standard value.

Answer: (C)