Here's why:

* Structure: Amino acids consist of a central carbon atom bonded to a hydrogen atom, an amino group (-NH2), a carboxyl group (-COOH), and a side chain (R group) that varies depending on the specific amino acid.

* Size: The basic structure of an amino acid is relatively small. The size of the R group can vary, but even the largest R groups are still relatively small compared to other biomolecules like proteins or carbohydrates.

While amino acids themselves are small, they are the building blocks of proteins, which can be very large and complex molecules.