A cell biology student examines an electron micrograph of a eukaryotic nucleus. Within it, a darkly staining region appears denser than the rest. Cells engaged in heavy protein synthesis (like liver and pancreas cells) have especially prominent versions of this region.
What is the primary function of the structure highlighted in red?
- A
Storage of mitochondrial DNA
- Bcheck_circle
Site of ribosomal RNA synthesis and ribosome subunit assembly
- C
Synthesis of mRNA exclusively
- D
Formation of the nuclear envelope
Explanation
The nucleolus is a dense region within the nucleus where rRNA is transcribed and joined with proteins to form ribosomal subunits.