Which of the following are not polysaccharides?

The choice identifying elastin as the correct answer to the question is accurate because elastin is a protein, not a polysaccharide. Polysaccharides are carbohydrates that consist of long chains of sugar units (monosaccharides) linked together, and they typically serve structural or energy storage functions in living organisms.

Alginate, cellulose, and dextran all fit the definition of polysaccharides. Alginate is a polymer derived from the cell walls of certain brown algae and is made up of mannuronic and guluronic acid residues. Cellulose is a fundamental component of plant cell walls, composed of long chains of glucose units, providing structure and support. Dextran is a polysaccharide made from glucose, produced by certain bacteria, and is often used in medical applications to increase blood volume or as a plasma substitute.

Thus, the distinction lies in the fact that elastin differs fundamentally in its structure and function, being composed of amino acids and serving roles in connective tissue elasticity, rather than being a carbohydrate-based structure.