A Brief Introduction to Cell Biology
The last couple of years I have been engaged in research in the field of plant cell biology, in particular, I am concerned with the signaling and regulation of cellular processes. In my spare time I indulge in bioinformatics, classical ML tasks, and sports biomechanics. This spring, I happily swam into the real world and communicated with real people, which allowed me to understand how little an ordinary person knows about how his body and the world around him are organized. This prompted me to write a series of articles on how our body is arranged, how cells work and how information is finally stored in DNA (detailed descriptions are, alas, very rare, but there is not enough knowledge about 4 nucleotides to understand the work of DNA). But I'll start perhaps with the simplest, with the composition of cells (for starters in a very simplified form).
It's no secret that almost all living things in this world consist of cells, whether we are with you, your beloved cat, seaweed, or bacteria that help digest everything that a modern person is loading his stomach. However, most people know almost nothing about how the cells are arranged and how they work. Many of you may object that their work is not related to biology and they do not need this knowledge, and this is your right. However, in most of the pressing problems, biological knowledge can help us (for example, to understand the absurdity of advertising most anti-aging creams, the importance of antibiotics and their correct intake, the absurdity of GMO controversies, etc.).
For starters, to what extent do cell sizes vary? One of the smallest cells is Mycoplasma genitalium. In fact, it is a small parasite living on the mucosa of primates (genital + respiratory tract). And it's really small, about 300 nanometers in diameter (who forgot, the nanometer is ??? meters). The largest cell is an ostrich egg. Yes! It's just one cage, just unusually large. The average cell of our body is about 5-20 microns in diameter. What would be clearer, comparable with a simple sheet A4.
Actually, there are a lot of cells in our body, and according to various estimates it is a lot from 1 to 100 trillion. Last time I came across a figure of 37 trillion, we will stop on it. The cell consists of a membrane, various "organs", called organoids. The rest of the space in it is filled with cytoplasm.
The nucleus of the nucleus is
We are used to having one nucleus in a single cell, a maximum of 2. In fact, there are noticeable emissions from these data. So infusoria shoes 2 cores, and in necrophages they can be up to a hundred. The core belongs to the two-membrane organoids, that is, surrounded by two membranes, controlling the transport of substances into and out. It contains almost 99.9% of the entire DNA of the cell, and it contains exactly the hereditary information necessary for the cell. Storage of DNA is not the only task of the nucleus, it also carries out synthesis of ribosomes, which I will discuss later.
In the cells of eukaryotes, they are responsible for the production of energy (in addition to a couple of energy production ways that we will not talk about yet). Usually in the cell several mitochondria and their combination is called mitochondrion. Like the nucleus, mitochondria are also a two-membrane organoid. However, the membrane structure differs from the nuclear one, but we will not complicate it. Mitochondria are often called semi-autonomous organoids. Why? Because inside the mitochondria contains its own DNA, which encodes part of its own enzymes and participates in the regulation of the work of the organoid. They also have their own protein synthesis system. By their size, mitochondria are reminiscent of bacteria. And it is worth noting that there is a theory of their bacterial origin. It is assumed that the ancient ancestors of modern eukaryotic cells entered into a symbiosis with ancient bacteria that "moved" to live inside cells. Cells provided them with a constant environment and an influx of all the necessary elements, so that bacterial cells, in the course of evolution, lost already unnecessary genes for survival in harsh environmental conditions. In turn, they have become a sort of factory for the transformation of compounds like glucose into ATP (the form of energy, which is mainly used by the cell).
Unlike previously described organoids, lysosomes have only one membrane, and as you can see they are much smaller than the nucleus or mitochondria. The lipid membrane of the lysosome contains bullets of hydrolytic enzymes. Despite its size, it participates in a number of processes. So she digests large polymers of proteins and carbohydrates that have got into the cage; can also digest old (broken) cellular organelles; participates in immune responses (with their help macrophages digest harmful bacteria); regulates the growth processes and finally participates in a number of signaling pathways. But we still remember that they are involved in the digestion of various substances trapped in the cell, for their further use in the biosynthesis of cellular structures, or in the production of energy by mitochondria.
Today I plan to finish my story with them. These organelles are membrane-free. And in themselves they are the smallest (except for individual elements of the cell skeleton and single enzymes). Created in the nucleus and fed by ATP produced mitochondria, they intensively synthesize cellular proteins (ranging from small signal proteins, ending with enzymes and large cellular structures such as ion channels, etc.). In the cell there are a huge number of them, according to various estimates from 1 to 5 million. It should also be noted that there are two types of ribosomes, the first, the larger one is located in the cytoplasm of cells, the second is characteristic of the inner contents of the mitochondria.
I still have not talked about such important components as the Golgi complex and the endoplasmic reticulum. But about this later.
Let's summarize and form a logical chain of what is happening.
The kernel contains information that regulates the work of the whole cell. Externally supplied substances, if necessary, are digested in lysosomes, and decay products are used to synthesize the components of the cell and produce energy, which is responsible for the mitochondria. The spent energy is used to synthesize proteins by ribosomes, both inside the mitochondria and in the cell cytoplasm.
It may be interesting