What is the function of nucleoli in the cell?

The nucleolus is a specialized structure within the nucleus of eukaryotic cells that plays a critical role in the synthesis of ribosomal RNA (rRNA) and the assembly of ribosomes. Ribosomes are essential for protein synthesis, as they serve as the sites where amino acids are linked together to form proteins based on the sequences of messenger RNA (mRNA).

Within the nucleolus, rRNA is transcribed from DNA, and it combines with ribosomal proteins imported from the cytoplasm to form the subunits of ribosomes. This assembly process is crucial because ribosomes are necessary for translating genetic information into functional proteins, making the nucleolus integral to cellular function and growth.

The other choices pertain to different cellular processes: protein synthesis (while related, is primarily the function of ribosomes once they are formed), DNA replication (occurs at specific sites within the nucleus and involves different structures), and cell division (a complex process involving various parts of the cell including the nucleus, but not specifically tied to the function of the nucleolus). Understanding the specific role of the nucleolus helps clarify its importance in the overall process of gene expression and cellular activity.