Nucleus: Think about your favorite superhero. Regular person by day, vigilante in spandex, and a cape by night. Saving the world isn’t an easy job, so most superheroes have support. Enter the guy behind the computer, the allknowing tech whiz that helps the hero succeed, hacking blueprints, giving directions during surveillance. The guy behind the computer does it all.
And we can think of the cell nucleus like the guy behind the computer, making calls, sending directions, and overall being in charge of the superhero cell, despite always getting less credit than the superhero themselves. The nucleus is a multifunctional organelle that is found in eukaryotes. Generally, eukaryotes have only one nucleus, but this isn’t always the case. Certain eukaryotic cells, like red blood cells and prokaryotes, like bacteria and archaea, don’t have nuclei either.
These are called enucleate cells. Other cells, like those of slime mold, have two or more nuclei and are called multinucleate cells. The nucleus, if there is one, makes up approximately 10% of the cell’s volume and has an incredibly important purpose in the cell. The cell nucleus functions as the information processing center of the cell, storing genetic material and organizing all of the cell’s activities, from cell division to synthesizing proteins.
The nucleus is especially important for protein synthesis. Oh, yeah. It’s the site of transcription, where messenger rna, or mrna, is produced. The nucleus may appear to be one lone blob of an organelle, but in fact, it’s made of many different structures that contribute to the overall function of the nucleus. We’re talking about the nuclear membrane, the nucleoplasm, chromatin, and chromosomes, and the nucleolus.
Now, let’s see what kind of programs the guy behind a computer nucleus runs in the superhero cell. The first important structure making up the nucleus is the nuclear envelope. The nuclear envelope is like your computer’s antivirus. It keeps everything where it should be and screens for everything before allowing it on your computer, or in this case, the nucleus. You can’t be a superhero sidekick with a virus on your computer, can you?
The nuclear envelope consists of two phospholipid bilayers that act as a wall for the nucleus, keeping all of the contents in place. This protective envelope is actually composed of two membrane layers, an inner nuclear membrane, or INM, facing inside towards the inside of the nucleus, and an outer nuclear membrane, or ONM, facing away from the nucleus towards the cytoplasm of the cell. The ONM also connects directly to the rough endoplasmic reticulum and is covered in ribosomes.
There is also a fluid filled space between the INM and the ONM called the perinuclear space separating the two membrane layers. Although the nuclear envelope acts as a wall to keep the nucleus in shape, it also has another important function, selectively allowing things into the nucleus. Small holes in the envelope, called nuclear pores, act as a safe passageway for different molecules, like proteins and rna.
The pores are like a bodyguard. Unless you pass the check, you’re not allowed entry. And this keeps the nucleus safe and allows it to keep doing its job without issue. Next up, let’s talk Internet. The guy behind the computer can’t function without Internet, right? That magical, hidden network that can get you anywhere you need to go. Much like the nucleoplasm of the nucleus, the nucleoplasm, composed of water, salts, enzymes, and other organic molecules, helps the nucleus in a number of ways.
First, it acts as a cushion for the nucleus, protecting all of the contents within the organelle, and also helps the nucleus keep its shape. But more importantly, the nucleoplasm acts as a transportation network for the nucleus, much like the Internet of the cell. Imagine you’re helping a superhero on a mission and search up bad guys near me, and you immediately get the perfect website back on your browser. Because of your super fast Internet.
The nucleoplasm works in sort of the same way. Say the nucleus needs something like an enzyme, for example. The enzyme travels through the cell, right through the nuclear pores, into the nucleus. It’s like cellular level Internet, but cooler. Now, let’s think about how a computer actually works. If you’re a superhero’s right hand man, you have to have a top notch, state of the art computer, and you can’t run a computer without code.
The code on your computer dictates how every single thing on it runs, so it’s really important. Chromosomes are like usb sticks for computers, but instead, they store the blueprint to our bodies. They store and share code in the form of DNA. Chromosomes have all our bodies information from howto manuals on cell growth to development and reproduction 101. Chromosomes live in the nucleus, but in a resting form when the cell is not in active reproduction stage, chromosomes exist in long, free floating strands of dna and protein called chromatin.
And chromatin can be classified even further into heterochromatin, the inactive form of chromatin, and euchromatin, the looser, more delicate form of chromatin. Chromatin in all its forms, comes together during cell division to form chromosomes. The nucleolus is the final feature we’ll talk about, and it actually directly relates to chromosomes and chromatin. Think of the nucleolus like a temporary line of code that your guy behind the computer uses to save the day.
It’s put on your computer to finish one job, and once it’s done, the code disappears until you need it again. The nucleolus is a membraneless feature that spends its time floating around in the nucleoplasm and also plays a big role in protein synthesis. The nucleolus, which stores proteins and rna inside, has features called nucleolar organizers that are integral for creating ribosomes during the process of protein synthesis.
Ribosomes are formed during protein synthesis, and then when the cell is ready to divide, the nucleolus disappears. Talk about not taking credit for your work. In an almost but not quite divided cell, the nucleolus reappears as sets of chromosomes meet on the opposite sides of the cell during mitosis. Like a line of disappearing code, the nucleolus fulfills its job, then lets the rest of the cell take charge, much like your favorite superhero depends on their guy behind the computer.
And let’s face it, the computer itself, our entire body, depends on the function of the nucleus. Whether it’s providing code for our bodies to replicate DNA or make new proteins, or it’s simply helping the necessary coding information pass through to be read by the nucleus, the various functions of this organelle are something we literally could not live without.
This episode is brought to you by the music for scientist album, now available on all streaming services. For more than a billion years, the only life on earth were single celled organisms without much of an internal structure. We call them prokaryotes, and they include bacteria and archaea. Then, about 2 billion years ago, something groundbreaking happened. Some of these organisms developed an internal compartment where they started storing their genetic material, the nucleus.
Having a compartment like this may not sound like a big deal, but this more organized structure paved the way for life to become multicellular and for it to diversify into plants, animals, fungi, and algae. A whole new group we call the eukaryotes. Now, almost every cell in our bodies has a nucleus that protects our genetic code and commands the activities that keep us alive. So, given all that, you’d think we’d have a solid idea of how the nucleus evolved and why.
But we don’t. Scientists do have several ideas, though, and exploring them can give us clues as to how complex creatures like us came to be. Now, the basic textbook explanation of how the nucleus evolved is called envagination. In this hypothesis, a prokaryote’s outer membrane folded inward to form a cavity. That’s actually why it’s called envagination, because it’s similar to the word vagina, which essentially means a cavity.
Regardless, over time, lots of imaginations created little wrinkles and pockets inside the cell. Then those infolds pinched themselves off, forming self contained bubbles, one of which happened to surround the cell’s genetic material, and voila. You’ve got a nucleus. This hypothesis offers a simple and elegant model of nucleus formation. Plus, it explains a few things about why the nucleus looks like it does. For instance, it explains why the nucleus is surrounded by a double membrane instead of just a single one.
Because when the outer membrane folded in on itself, it doubled up. But despite what textbooks say, there are a few reasons that this explanation doesn’t hold water. The big one is that we can’t explain why it would happen. Like, what would make a cell just start folding in like this? It doesn’t make sense that it would happen just to create a pocket to protect genetic material, because imagination involves lots of folds creating several different structures.
To answer this, some researchers have proposed that the infolds evolved for feeding and acted like mouths. Then the nucleus formation was just a side effect. But that’s a pretty important side effect for something that stuck around for billions of generations. Also, imagination by itself just isn’t great at explaining other features of cells, like the evolution of some of their organelles or mini organs. One of these is the mitochondria, which are the energy centers of cells.
The classic imagination hypothesis says mitochondria evolved from material that was already in the cell. But mitochondria have their own separate dna. Really? It seems like they were once another organism that somehow got inside the cell. So eventually, scientists came up with other hypotheses to better explain the evolution of both the nucleus and mitochondria. The most famous of these is endosymbiosis. It’s a really popular idea, and over the years, scientists have proposed at least 20 versions of it.
The basic idea of all of them is that at some point in history, one prokaryote swallowed another one, but didn’t digest it. Scientists aren’t sure which prokaryotes were involved, but most of them think anarchean swallowed a bacterium. Then the bacterium just kind of hung around, and the two provided mutual benefits to each other, like offering protection and sharing energy and nutrients. In the end, this friendship lasted so long that eventually the bacteria evolved into mitochondria.
And either before or after that, the nucleus formed through imagination. So this model is a little more complex, and it does solve some things, but it also has its own problems. Like there’s a sort of chicken and egg thing with the mitochondria themselves. It takes a lot of energy for one organism to swallow another. And the way organisms typically get lots of energy is from mitochondria. So how did the archaea get the energy to eat that bacterium in the first place? It’s the question we can’t answer.
Also, this hypothesis retains a lot of the original problems with pure envagination too. Like, why would it happen? So, in 2014, scientists proposed another hypothesis about how the nucleus got here that dodges these problems altogether. It’s called the inside out model, and it takes a pretty different approach. In this idea, the starting point was an archaeal cell that had bacteria living on its outer surface. To feed on these bacteria, the archaean oozed blobby protrusions from its outer membrane, which very serious scientists have named blebs.
And the blebs trapped the bacteria between them. Then the archaean took some of the bacteria’s energy and used it to grow and swell its blebs so that it would have even more surface area to trap and feed on more bacteria. And eventually the blebs completely engulfed the bacteria and incorporated them into the cells. In the end, the bacteria went on to evolve into mitochondria, and the archaean itself turned into the nucleus and the blebs became so large that they evolved into a few different things, including the cell’s outer membrane, but also the outer membrane of the nucleus.
Overall, the inside out hypothesis has several things going for it. Like, it explains why nuclei have a double membrane, but also it jibes with things archaea actually do, because they really do form blebs. Like in 2020, researchers described an archaeal cell that has a nucleuslike cell body with bleblike protrusions. And they may use these protrusions to exchange material with organisms living on the cell. So there is precedence for this sort of thing.
Also, this cell is an Asgard archaea, which scientists think are the closest living relatives of the archaea that became the first eukaryotes. And beyond all of that, this hypothesis also explains why and how the nucleus evolved. It was basically a side effect of an archaean trying to interact with bacteria living on its surface. Now, that said, there’s still one piece missing. If the nucleus were originally a standalone archaean, it would have had the ability to take the information from its DNA and use that information to make proteins.
So theoretically, there should be machinery for protein assembly inside the nucleus, and there isn’t. In eukaryotes, DNA is copied into another molecule called rna. And then rna leaves the nucleus and goes to make proteins elsewhere in the cell with the help of another organelle. So how did that happen? Well, some scientists have proposed a fourth hypothesis that’s pretty controversial, but also pretty fascinating. Giant viruses. Scientists discovered these in 2003, and they’re roughly the size of bacteria, which is huge compared to normal.
Like many viruses are half that size or less. These giants enter cells and then build compartments called viral factories, which the viruses use to replicate themselves. And there are a couple of interesting things about these factories. First, the process of copying DNA takes place inside them, while the construction of the proteins happens outside, which sounds a little bit like what happens inside and outside of the nucleus in eukaryotes. Secondly, giant viral factories happen to be roughly the size of a nucleus.
So there are two ways these viruses could have played a role in the evolution of these key structures. In one version of the hypothesis, a giant virus infected an archaean and built a viral factory. The virus stole genes from the archaean and stashed them in the factory, and then over time, it evolved into the nucleus. This is great in that it explains why a nucleus would form. As a mechanism of protecting DNA, the virus needed somewhere safe to set up shop and replicate.
And if it’s true, it means that inside every one of your cells are the remnants of a giant virus, which is a little disturbing. Now, the other version of this hypothesis starts the same way. A giant virus infected an archaean and built a viral factory. But in this scenario, the viral factory surrounded both the virus’s genetic material and the archaeans. Then the archaean learned from the virus how to make a factorylike compartment of its own to protect its precious genetic material.
Overall, this idea that an ancient virus infected a prokaryote is plausible, because we do see that happening today. Like in 2017, researchers found a virus that infects bacteria and builds viral factories inside of them. And in 2020, scientists discovered that another virus forms viral factories that have double membranes. The downside is neither of the giant virus hypotheses explain how these things could have happened.
For example, there’s no explanation of the evolutionary process that would have turned a viral factory into a nucleus. Also, scientists haven’t yet found a giant virus that builds viral factories inside archaea specifically. So in the end, despite it being this fundamental thing about us and complex life on Earth, we still don’t know where the nucleus came from.
And the only way to sort it out is to do more research. Fortunately, scientists are constantly discovering new archaea, bacteria and giant viruses in places as diverse as the bottom of the ocean and inside your mouth. And the more we find out about these ancient organisms, the closer we’ll get to understanding how nuclei formed and how we came to be.
Now, if you enjoy thinking about big questions and mysteries like this, you might also be interested in the music for Scientists album. It was inspired by the beauty of science as it pushes the boundaries of our understanding and our view of the world. And it’s a tribute to those who’ve dedicated themselves to science driven work. If you want to check it out, you can click the link in the description to start streaming
Why do RBCs lack nuclei and mitochondria? It’s a very, very interesting questions, and many of you are asking for the answers. So here we are with the answers. So let’s get started. When we talk about the living organisms, we know that we, all living organisms are made up of cells, and cells are the structural and the functional unit of life. They plays a very, very important role. Cells will be coming together and they will be forming the different tissues.
Tissues will be coming together and forming the organs. Now, different organs are there, and these organs will be coming together and forming the organ system. And after that we will have the organism. So if we start from the very beginning, cells plays a very important role. And then when we talk about the cells, these cells can perform all of these amazing function because they have different organelles. Now, these different organelles are really very important.
They have very specific functions, and these specific functions actually help the cells to perform various metabolic activities that happens in the individual. So all of these organelles have a very huge responsibility to play. When we talk about the nucleus, we call it as the master brain of the cell, right? It’s a brain of the cell, and it’s really very important. And when we talk about another organ, which is the organelle, which is the mitochondria, it plays very important role in the production of the energy.
Apart from that, we have different organelles that have this specific function and that are really very important. When we talk about the RBCs, there is some change over here. So let’s talk about that. Now, when we talk about the RBC, RBC is really very special. First, of course, a unique characteristic feature about the RBCs or the red blood cells is that they have the very unique shape. They have biconcave disc like shapes over here we can see, right. They have a very disc like shape.
Now, this shape actually plays a very important role in increasing the surface area. This is very, very important. This actually shape, right. Helps in increasing the surface area. Now, this plays a very important role, further, that they actually help in the transportation of oxygen. Apart from that, when we talk about the rbCs, they can easily squeeze and can swell and can move easily from the small capillaries without getting damaged.
So this particular biconcave shapes plays a very important role now that we are clear about the structure, and we know that why it is helpful for the RBC. Let’s talk about more over here. We will be discussing about the no nucleus in rbCs. Yes, in rbCs, we don’t have the nucleus. So we have over here a mature RBC. In the immature RBC, or a very young RBC, all the organelles are present. But as it matures, what happens? We will see that these organelles will not be there.
Now, whatever important requirements are there for the RBCs in terms of the genetic material, proteins, right. All of that will be getting synthesizer ready in the immature phase and will be used up in the future. Now, there’s a very interesting fact about the RBC. I’m sure you’re already aware that the lifespan of the RBCs is about 120 days. So whatever important components or the chemicals which is required, the RBCs will have from their immature phase to the mature one as they enter and as they mature.
Right. They will not have nucleus or any other organelle. The reason that the RBCs don’t have the nucleus is a very simple reason. Nucleus will be occupying a lot of space. And of course, the RBCs need that space for something really very important. So they don’t have the nucleus. And that’s a very important point. Please note this down. Now, let’s talk about another organelle. Now, nucleus is fine, but what about the mitochondria?
To our surprise, RBCs don’t have the mitochondria. Also, we know that mitochondria plays a very important role in the synthesis of the energy, and they required oxygen, right. For that process to follow. Now, if we have the mitochondria in the RBC, what will happen? Now, of course, we can say that it takes a space, but apart from that, it has a very, very important function. I’ll give you few seconds to think about it. I’m sure you have the answer in your mind.
So let’s quickly find out that what will happen if we have the mitochondria inside the cells? Now, if we have the mitochondria and the rbcs, they will be using up the oxygen, right? And rbcs needs to carry this oxygen to the different parts of the body. So if the mitochondria is there, the oxygen will be kind of divided between the rbcs. And of course, the mitochondria will also have its own share of oxygen. That’s why mitochondria is not present, so that all the oxygen can be easily carried by the hemoglobin protein, which is present in the rbcs. That’s a very important point.
Then comes a very important question, which is there on, in our front or in our screen, right. That if rbcs don’t have the mitochondria, from where they get the energy. So we know that there are two types of respiration, aerobic respiration, where there’s a requirement, or the presence of the oxygen. And then we have another type, which is the anaerobic respiration, which happens in the lack of oxygen or in the absence of oxygen.
So our rbcs get the energy from the anaerobic respiration. Very, very interesting fact, right? You can learn more about it, and I’m sure you’ll be amazed to know that, how these interesting rbcs actually do the respiration. Now that we are clear with that, we can say that our rbcs are keeping us alive. We know that they plays a very important role in the oxygen transportation. They carry the oxygen, right? And of course they carry the carbon dioxide also, so they helps in the exchange of the gases.
We know that in rbcs we have hemoglobin, which is a pigment protein, right? And because of that, only the rbcs are red in color and hemoglobin is the one that will be carrying the oxygen. So these are the important points. So we have to conclude that why the rbcs lack the nucleus of the mitochondria. First, of course they need that space so that they can carry more oxygen. And second, if they carry the oxygen, if the mitochondria is there, mitochondria might use the oxygen.
These are the two important reasons that we have to remember about now. I hope that you have the clarity about the answer. And over here we are done. And here is a homework question for you. You can actually find out that why the deficiency, especially the iron deficiency, causes the low hemoglobin count. That’s a very interesting question we have discussed about the hemoglobin.
Write about it and if I give you a hint, I’m sure that it will become really very easy. But you can easily find the answer for this. It’s a very interesting question. You can write the answer in the comment section below and we will be happy to reply. And we’ll be reading out your comments, so we’ll be waiting for your answer. Go to Home
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