Final answer:
The nucleolus is primarily responsible for the transcription, processing, and assembly of rRNA into ribosomal subunits, which are then exported to the cytoplasm for protein synthesis. The correct answer to the question is 1) rRNA subunit assembly.
Step-by-step explanation:
The nucleolus is a critical structure within the nucleus of eukaryotic cells that performs several important functions related to ribosome synthesis and assembly. Its primary role is to serve as the site where ribosomal RNA (rRNA) is transcribed, processed, and assembled into the large and small subunits of the ribosome. These newly formed ribosomal subunits are then transported out through the nuclear pores into the cell's cytoplasm, where they will participate in protein synthesis.
Given the choices you provided:
- rRNA subunit assembly
- Telomerase assembly
- Subunits of ribonucleoproteins
- A and B only are correct
- A, B, and C are all correct
The correct option is 1) rRNA subunit assembly. While the nucleolus does aggregate rRNA with associated proteins to assemble ribosomal subunits, there is no evidence in the provided references to suggest that it is the site of telomerase assembly. Therefore, this eliminates options 4 and 5.