Which option is not a major class of natural polymers?

Natural polymers are typically derived from biological sources and play significant roles in various biological processes. Major classes of natural polymers include polysaccharides (like cellulose and starch), which are composed of sugar monomers; nucleic acids (like DNA and RNA), which are essential for genetic information storage and transfer; and proteins, which are polymers of amino acids and perform numerous functions in cells.

The option that is not classified as a natural polymer is polyethylene (PE). Polyethylene is a synthetic polymer made from petrochemical products through polymerization processes. Unlike the other options, which occur naturally in living organisms and are crucial for life, polyethylene is engineered and widely used in manufacturing plastics for various applications. Its origin from non-renewable resources and its synthetic nature distinctly separate it from natural polymers, which are derived from renewable biological sources.