Functions of the Nucleolus

What are the functions of the nucleolus?

A) DNA replication

B) Protein synthesis

C) Cell division

D) Ribosome biogenesis

Correct Answer: D) Ribosome biogenesis

Explanation:

The nucleolus is a non-membrane bound organelle found within the nucleus of eukaryotic cells. It is primarily responsible for the production of ribosomes, which are the cellular structures responsible for protein synthesis. The nucleolus carries out several functions related to ribosome biogenesis, including:

1. Ribosomal DNA (rDNA) transcription: The nucleolus contains the genes responsible for the production of ribosomal RNA (rRNA), which is a critical component of the ribosome. The nucleolus transcribes and processes this rRNA to produce the subunits of the ribosome.

2. Ribosome assembly: The nucleolus is responsible for the assembly of the subunits of the ribosome. The subunits are assembled in the nucleolus and then exported to the cytoplasm where they combine to form a functional ribosome.

3. Ribosome maturation: The nucleolus is involved in the processing and modification of the rRNA that is necessary for the proper functioning of the ribosome. This includes adding and removing specific chemical groups to the rRNA.

To better understand the functions of the nucleolus, let's consider an example. Suppose a cell needs to synthesize a protein. The first step in this process is the transcription of DNA into mRNA in the nucleus. Once the mRNA is synthesized, it is exported to the cytoplasm where it can be translated into a protein by the ribosome. The nucleolus plays a critical role in this process by producing and processing the subunits of the ribosome that are required for protein synthesis.

In conclusion, the nucleolus is primarily responsible for ribosome biogenesis, including rDNA transcription, ribosome assembly, and ribosome maturation. The ribosome is a critical cellular structure responsible for protein synthesis, and the nucleolus plays a critical role in ensuring that the ribosome is properly assembled and functioning.