Intro to The Nucleolus — The Heart of Creation
Many people think of the nucleus as the “brain of the cell”, which is a cute little human-centrist analogy. We all need little analogies to relate to things from time to time don’t we? It’s a far from perfect comparison, but it isn’t the absolute worst one. If the brain does the central computation of the organism, the nucleus does indeed contain the genetic material, which is copied, transported and translated into its final end products: Proteins and enzymes which are integral to the functioning and structure of life, and amongst the most complex of chemical processes we know.
Note: I’m thankful to live in the modern day and age when all this information is freely available and composable, thanks to the efforts of countless others who came before me. All relevant links to primary and secondary sources have been posted on the term, and for any that sources I have missed citing, I will work to update this to include those references.
Disclaimer: None of the literature contained in this article is medical advice or to be taken as medical advice. This article is for informational purposes and potentially subject to errors which I’m constantly working to correct. Consult a physician if you have a medical issue.
However, inside the nucleus resides something even more fundamental: The Nucleolus! Or “little nucleus”. The nucleolus, unlike the nucleus doesn’t contain a nuclear membrane, and thus isn’t a so called membrane bound organelle. Rather it is a free floating “nuclear region” that has different chemistry, structure and cytoplasmic composition than the rest of the nucleus. Some cells can have multiple nucleoli — most often 2 or 3, but on rare occasion, thousands of nucleoli can be present in certain cells, particularly those with prodigious protein production capabilities.
So what is the purpose of this mysterious little non-walled off, yet distinct region of the cell? Anyone who’s cell biology enthusiast will be able to rattle off nucleolar factoids like they can remember the birthdays of their immediate family members! Thus, next I present you with the most important factoid, and also the reason I titled this piece, rather dramatically “The Nucleolus — The Heart of Creation”: The nucleolus is where the ribosomes of the cells are manufactured via an ultra-complicated and not fully as of yet understood sequence of biological processes.
Ribosomes!
Not to go on too much of a tangent here, but you can’t really have a discussion on the nucleolus without talking about its all important products: Ribosomes. If there’s anything that’s the equivalent of the actual programmer/computer of the cell, and essentially the fundamental “computer” of life, it would have to be the Ribosome.
Ok I’m going to skip a WHOOOLLLEEE lot of foundational information here for the purposes of a 300 foot overview, but I will do deeper dives in the future into the prerequisite topics that under-gird the function of the nucleolus.
To quickly recap the Central Dogma of Biology, DNA is copied into a flexible, volatile copy itself called mRNA by an enzyme called RNA Polymerase in a process called Transcription. This messenger RNA is carried off outside of the nucleus via the nuclear pores, into the cytoplasm of a cell, to a flee floating Ribosome. The structure Ribosome itself is highly intricate combination of ribosomal RNA and a protein scaffold whose exact mechanism of action is way beyond the scope of this article, but I digress.
The Ribosome, which reads each “codon” (3 letter nucleotide sequence of RNA, which is similar to a computer instruction) “waits” for and captures a very specific transfer RNA. This tRNA carries an Amino Acid corresponding to the codon it happens to be reading at the time, based on the Genetic Code, and it’s done for the entire length of the mRNA strand being read by the ribosome — This process is called Translation. Also Remember: Amino acids are the building blocks of proteins.
While this is happening the Ribosome strings each amino acid together, via peptide bond formation, until the code ends, all a part of a process called Protein Production. Proteins and Enzymes, in their aggregate, are the machinery of the cells and the mechanism by which they perform their millions of complex functions. This, in a very tight nutshell, is how life is created — at least here on earth. And it’s also how Ribosomes are the “programmers of life”. I’ll have an entire series of articles one day on how Ribosomes function in depth, which will no doubt be a doosey. Suffice to say that these little wonders of science are all manufactured in the Nucleolus.
Also, just because it’s interesting to compare unique extremes, sperm cells typically have no nucleoli, because they don’t need to produce additional ribosomes. Their purpose is to swim rapidly and inject their contents into the egg, and they already upon inception have what they need to carry out their function. On the other hand, egg cells when combined with sperm cells in a form called oocytes have a tremendously large number of nucleoli. They have thousands of them, which leads to production of trillions of ribosomes per fertilized egg! This makes sense if you think about it because a newly developing embryo needs to create many structures in order to survive and grow.
Very recently, Lex Fridman did an interview with Betül Kacar, an Astrobiologist and Bacteriologist who talks at great length about the analogs between the biological translation machine and human made computers as we know it. She addresses some important differences and similarities, and basically presents a breathtaking framework around how the original of life arises from the natural, mysterious computational machinery embedded in nature, chemistry and the universe itself
First Detection and Visualization of the Nucleus:
The nucleolus was first discovered in the 1850s, by scientists using visual microscopy techniques, but its function wasn’t really appreciated until the 1950s, when the nucleolus of starfish were first observed and then later the nucleolus of frogs where it was determined by observing frog eggs, that those without a nucleolus were all still born, and those with a nucleolus survived. At that point it was appreciated that the nucleolus wasn’t simply some biological curiosity, but an actual important part of the cell and of propagating life.
Conclusion
Well that’s the nucleolus at a high level! As usually there are plenty of videos about the nucleolus out there, as well as several articles and wikis to glean this information from, but I thought it would be a good start to my biological structures series to go a bit into the nucleolus, because despite how important it is, it’s often overlooked, especially in introductory cell biology treatments. That, and also the word nucleolus kind of rolls off the tongue, so I was compelled to write on it.
Appendix: Interesting Theory About RNA
One other fascinating thing about RNA if you are interested, is that in modern biology, at a high level RNA seems mostly like some kind of disposable intermediate. A “slave” molecule that was meant to carry the messages of far more enlightened “masters” called DNA, and mindlessly manufacture proteins as function of the aforementioned Ribosome. But countless millennia and eons ago, it was actually the other way around and RNA was running the show. RNA molecules were the masters of the planet, and they multiplied, proliferated and even predated on other molecules with abandon. This is the so called RNA World hypothesis, and is a fascinating theory in its own right.
Thanks for reading! Hope to be back soon with a part II, to discuss the internal structures of the nucleolus.
