The cell structure made up mainly of globular RNA is the ribosome.

Here's why:

* Ribosomes are the protein synthesis factories of the cell. They are composed of two subunits: a large subunit and a small subunit.

* Ribosomal RNA (rRNA) is the primary component of both subunits. rRNA molecules fold into complex, globular structures, forming the core of the ribosome.

* Proteins also play a role in ribosome structure, but the majority of the ribosome's mass and structure is contributed by rRNA.

While other structures like the nucleolus contain RNA, they are not primarily composed of globular RNA.