To describe a main function of the nucleolus, you must first
understand its location and structure. The nucleolus is located within the
nucleus. It is not bound by a membrane, but, it has a huge aggregation of
macromolecules. These macromolecules include; rRNA-processing enzymes, large
assembly factors, and ribosomal proteins. The size of the nucleolus can vary
depending on the number of ribosomes cell is producing (Alberts et al. 2015).
This is one of many main functions, ribosomal biogenesis.
biogenesis takes part in the nucleolus is a very complex process and a very
important one. Ribosomes in the cell play a key role in protein synthesis, as
they help in the linking of amino acids during translation. Without them, the
cell will not survive for long. This all starts with formation of ribosomal RNA
(rRNA) from five pair of chromosomes and its collection within the nucleolus
(Guyton et al. 2011). Once inside the
nucleolus, transcription takes place and many precursor rRNA are formed. These
precursor rRNA are then packaged tightly by ribosomal proteins made in the
cytoplasm and from their ribonucleo protein is formed. This, unfortunately,
cannot pass through the pores of the nucleolus and a specific rRNA enters from
the cytoplasm to break this down into two fragments, 5s rRNA (Alberts et al.
2015). This can readily pass through the nucleolus and ribosomal formation
takes its final steps in the cytoplasm.
But, the nucleolus
is not just used for ribosomal biogenesis. This nucleus organelle is a key
player in keeping cellular homeostasis (Grummt 2013). Cellular stress can be
caused by any variable factors, when this happens the response is vital for
cell survival. When cellular stress occurs, the nucleolus transmits these
signals to RNA polymerase I. This in return will begin a serious of cellular
functions to halt, specifically ribosomal biogenesis (Grummt 2013). The main
reason for ribosomal biogenesis is one of the key cellular functions to halt is
due to the sheer amount of energy expelled by the cell and availability of
nutrients is key for cells. These inhibitions in return will halt protein
synthesis, growth, and many other functions. This will allow the cell to
maintain homeostasis when it is under stressful conditions.
The nucleolar and
its functions are impressive. This organelle is a key player in cellular
survival. Two of the key functions described; ribosomal biogenesis and
maintenance of cellular homeostasis show that the slightest “hiccup” can be
detrimental to the very survival of the cell.
Alberts B, Johnson A, Lewis J, Morgan D, Raff M, Roberts K,
Walters P. How Cells Read the Genome. In: Molecular Biology of The Cell. 6th
ed. Garland Science; 2015. p. 299–368.
Hall JE, Guyton AC. The Cell and Its Function. In: Textbook
of Medical Physiology. 12th ed. Saunders Elsevier; 2011. p. 11–25.
Grummt I. The nucleolus-guardian of cellular homeostasis and
genome integrity. Chromosoma. 2013 accessed 2018 Jan 21;122(6):487–497. https://link.springer.com/article/10.1007%2Fs00412-013-0430-0#citeas