which best describes the molecule in the diagram below

The answer is; C.
This is because of its more or less spherical shape and its compactness. This is different from the other type of tertiary protein called fibrous protein - composed of long and narrow strands. Globular proteins have an irregular protein sequence and serve as functional proteins hence intricately folded due to the interaction of amino acid side groups. Their shape is pH sensitive. An example of a globular protein is hemoglobin.