Which best describes the molecule in the diagram below

The correct answer will be option-A.

Explanation:

The primary protein structure can form complex secondary structures which provide functions to the cells.  

The proteins usually take the form long sheet and fibre like structure made of long polypeptide chains known as "secondary structures of fibrous proteins". The secondary structure can fold into a spherical structure or globular structure which plays important roles in metabolic reactions. These proteins are called "globular proteins".

Since the figure shows a globular or spherical structure of proteins, therefore option-A is the correct answer.