The term “nucleus” dates back to 1831, when Robert Brown was observing the cells of plants, and noticed that it was present in all of them. Robert was not the first person to discover the nucleus, but he did coin the term for one of the most defining features of eukaryotic cells. It should be noted that nuclei are only part of eukaryotic cells, not prokayotic cells - read more about their differences here.
What is a Nucleus?
The National Human Genome Research Institute (NHGRI) defines the nucleus as “a membrane-enclosed organelle within a cell that contains the chromosomal DNA”[1]. It is the largest and stiffest organelle in animal cells, and, within mammals, it occupies approximately 10% of the cellular volume [2].
Figure 1. Nucleus stained purple.
Origins of the Nucleus
There is no consensus on the origin of the nucleus, but rather three hypotheses. The most popular hypothesis states that the Endoplasmic Reticulum (ER - read more here) expanded and eventually surrounded the DNA [3]. Therefore, the nucleus developed from the ER.
Functions of the nucleus
Storing and protecting the chromosomal DNA
Since the nucleus contains chromosomal DNA of a eukaryote, its primary function is to store and protect the genetic data. Chromosomal DNA is efficiently folded and packed. In fact, human cells has around 2m of DNA that is folded to fit within 10 microns (for scale, a grain of salt is 60 microns, therefore 2m of DNA is folded into 1/6th of a grain of salt) [4].
Facilitating communication between the genome and the rest of the cell
The nucleus is perforated by a series of massive protein complexes known as nuclear pore complexes (NPCs). These structures allow the movement of molecules between the inner nucleus and the rest of the cell - a process known as transcription (more information here). Through transcription, genes produce messages that are transported by NPCs to the rest of the cell. These messages notifies the cell about which proteins need to be produced.
Figure 2. Nucleus.
Messages can go in both directions. In fact, external stimuli from outside the nucleus - the external environment or within the cell - can set off a cascade of chemical reactions. Eventually, this cascade causes a molecule to move via NPCs and interact with the DNA. This interaction leads to the transcription of necessary proteins.
Mechanotransduction
The transfer of physical force - from cells’ movement or an external force - to the cytoskeleton is a process known as mechanotransduction. In this case, physical forces cause pressure towards the nucleus, creating a cascade of chemical reactions that will eventually elicit a molecule to interact with the DNA.
There are multiple ways to alleviate this pressure, ranging from the release of ions to the activation of genes. For example, mechanotransduction can lead to stem cell differentiation, which gives rise to all the different cells in the body [5], or it can prompt malignant behavior such as tumors [6].
Stay tuned for more future posts about genome and evolution!
—-----------------------------------------------------------------------------
Written by: Renard
Edited by: María and Natasha
Figures created by: Adrian
BioDecoded is a volunteer group committed to sharing accurate scientific information. If you have any questions about this topic or would like to learn more, please comment below or send us your questions.
References:
Nucleus (2023). National Human Genome Research Institute. Available at: https://www.genome.gov/genetics-glossary/Nucleus#:~:text=A%20nucleus%2C%20as%20related%20to,and%20out%20of%20the%20nucleus (Accessed: 17 January 2023).
Jagannathan, S. et al. What is the nucleus? (2023). MBInfo. Available at: https://www.mechanobio.info/what-is-the-nucleus/#:~:text=The%20primary%20functions%20of%20the,facilitate%20its%20transcription%20and%20replication (Accessed: 17 January 2023).
Martin, W. (2005). Archaebacteria (Archaea) and the origin of the eukaryotic nucleus. Current Opinion in Microbiology, 8(6), pp. 630-637. Available at: https://www.sciencedirect.com/science/article/abs/pii/S1369527405001608?via%3Dihub
Zooming In: Visualizing the Relative Size of Particles (2020). Available at: https://www.visualcapitalist.com/visualizing-relative-size-of-particles/ (Accessed: 17 January 2023).
Engler, A. et al. (2006). Matrix Elasticity Directs Stem Cell Lineage Specification. Cell, 126(4), pp. 677-689. Available at: https://www.cell.com/cell/fulltext/S0092-8674(06)00961-5?_returnURL=https%3A%2F%2Flinkinghub.elsevier.com%2Fretrieve%2Fpii%2FS0092867406009615%3Fshowall%3Dtrue
Paszek, MJ. et al. (2005). Tensional Homeostasis and the Malignant Phenotype. Cancer Cell, 8(3): 241-254. Available at: https://pubmed.ncbi.nlm.nih.gov/16169468/
Comments