What is the role of the nucleolus in a eukaryotic cell? (A) To provide a barrier between the nucleus and the cytoplasm. (B) To wrap around chromatin when forming chromosomes. (C) To act as the site for cellular respiration. (D) To initiate and control cell division. (E) To synthesize ribosomal RNA.
One of the defining characteristics of eukaryotic cells is the presence of the
nucleus to contain DNA. Let’s take a closer look at the nucleus and describe some of its parts so we can
answer our question.
The nucleus is surrounded by an inner and outer membrane that together make up the
nuclear envelope. The nuclear envelope separates the contents of the nucleus from the rest of the
cell. This protects DNA from any reactions that are occurring in the cytoplasm. The outer membrane is continuous with the endoplasmic reticulum, which you can see
here. Only a portion of it is shown for simplicity. But the endoplasmic reticulum surrounds the whole nucleus.
Surrounding the nuclear envelope are numerous openings called nuclear pores. These allow small substances, like mRNA, to exit the nucleus while keeping larger
substances, like DNA, inside the nucleus. Inside the nucleus is the DNA, and it’s chromosomes that are compacted in a state
called chromatin. Chromatin is a mixture of DNA and histone proteins. The nucleoplasm is the name of the liquid that surrounds the chromatin and contains
all the enzymes and nucleotides needed for DNA transcription.
And finally, the nucleolus is a region of the nucleus where ribosome subunits are
produced. Ribosomes are organelles involved in protein synthesis and are made up of proteins
and ribosomal RNA. The nucleolus is where this ribosomal RNA is produced and then incorporated into the
So, going back to our question, the role of the nucleolus in eukaryotic cells is
given by answer choice (E), to synthesize ribosomal RNA.