Question

1. how could you get an estimate of the size or weight of a particular polypeptide?

Explanation:

Gel - electrophoresis can separate polypeptides based on size. Smaller polypeptides move faster through the gel. By comparing the migration distance of the target polypeptide with known molecular weight standards (markers) in the gel, an estimate of its size (and thus an indirect estimate of its weight, as size and weight are related for polypeptides) can be made.

Answer:

Use gel - electrophoresis.