What should be done with the supernatant after centrifugation?

The choice to discard the supernatant after centrifugation is generally correct in the context of GFP purification when the goal is to isolate the protein of interest. During centrifugation, the cellular debris and precipitated proteins collect in the pellet at the bottom of the tube, while the supernatant typically contains soluble proteins, which may include unwanted components and contaminants.

In the purification process, especially when focusing on extracting the Green Fluorescent Protein, the ideal scenario is to concentrate on the pellet, which ideally should have had the target protein retained during the lysis and extraction processes. Therefore, once the centrifugation step is complete, discarding the supernatant makes sense to ensure that focus remains on the pellet, which can then be further processed to obtain the GFP.

It's important to note that there are instances in experimental procedures where the supernatant could be analyzed for other proteins or components, but in many GFP purification protocols, the emphasis is placed on the pellet containing the desired product. This is likely why the other options would not align with the objective of isolating and purifying GFP effectively.