Disaccharides store less energy than polysaccharides because disaccharides:

Disaccharides are sugars that are formed by two monosaccharides bound together, usually via condensation reactions. These are smaller and simpler sugars such as sucrose, and are not involved in energy storage. Polysaccharides are long chain carbohydrates that are involved in energy storage or structure. The main reason why these two differ from a biochemical point is the fact that polysaccharides are much larger molecules and have the ability to store larger amounts of energy between their bonds.

Allow large amino acids through