This article is a translation of a french article written by 
Source :
Cells are everywhere. It is the cells that make up our skin, our brain, our heart ... The red blood cells we talked about in the article on blood circulation are cells!
It's all well and good ... But concretely, what is it?
The cells are droplets of fat with an aqueous center, (= composed of water) that is called the cytoplasm. The fat layer makes up what is called the extra-cellular membrane.
On both sides of this cell membrane, we find:
- The extracellular space
- The intracellular space that we call the cytoplasm (I repeat, but it is the basis of pedagogy, isn't it?).
- These two spaces are of an aqueous nature (water).
Source : @Whentone
Translation: Milieu extra-cellulaire = Extracellular space / Cytoplasme = Cytoplasm / Membrane cellulaire = Cell membrane
And what is the utility of the cell ?
A cell is like a very sophisticated factory composed of many elements:
- The cell membrane
- A nucleus for eukaryotic cells (we'll talk about it later)
- Organelles: there are differents "modules" found in the cytoplasm. There are many of them and we will not see them all. Some are only found in a few types of specialized cells.
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The cell membrane:
The cell membrane serves as a fence for this factory, it separates the extracellular space from the cytoplasm.
If the cell wants to work, it needs materials. These materials will come from the extracellular space and will present themselves to the cell membrane that has ports and channels. If the materials have the proper shape, size or electrochemical structure they can enter. To make the cell work, it must also receive "commands". These commands are molecules such as hormones, growth factors, ... Hormones, growth factors will interact with the cell membrane, and goes through complex processes in order to transmit this demand to the nucleus.
The nucleus :
First of all, we must know that there are two major types of cells in the living world:
- Prokaryotes, which are cells without a nucleus
- Eukaryotes, which are cells with a nucleus
- The man is an eukaryotic being: all of his cells have a nucleus within them. There is an unique exception: the red blood cell, but it is still an eukaryotic cell, because it has a nucleus until a certain stage of its maturation. (a bit complicated to understand for our current level!)
The nucleus is a bag within the cell, which contain deoxyribonucleic acid or DNA (the famous!). To resume our analogy with the factory, the nucleus is the research and development center of our company.
Differents molecules will read the DNA, in search of what is required by the hormones, growth factors or by the cell itself. When they go to the part of the DNA that interests them, they will decode it and transcribe it into RNA or ribonucleic acid thanks to the genetic code! (I will explain in the future what the genetic code is)
The endoplasmic reticulum :
Our freshly created RNA will come out of the nucleus, gain the cytoplasm and go to the endoplasmic reticulum, which is the production line of our cell factory. Small workers called ribosomes will read this RNA, which can be compared to a manual explaining how to assemble different materials, to form more complex molecules. Once these molecules are created, they will migrate to the Golgi apparatus.
The Golgi apparatus:
The Golgi apparatus is the storage center of our factory, but a storage center allowing the maturation of these freshly designed molecules.
That's all ?
Of course not! We only scratch the complexity of the cells that compose us!
Our cells also have bins filled with acid, which are called lysozyme.
To operate the cell needs energy! This energy is produced by an amazing organelle that I particularly like: the mitochondria! (I'll do an article about this organelle that has an amazing story!)
To summarize and illustrate my words, I propose a link to visualize a diagram: Diagram of the cell
The products formed by the cell can then either stay in the cell, or pass the cell membrane to reach the extracellular environment.
There are other structures to discover, but I think that your heated brains need rest and time to assimilate all that we have just discovered ! 😊
I hope you enjoyed this post, if you have any questions or comments, I can reply to the comments!
See you soon,
Whentone
Sources:
What I swallowed and digested during my cell biology classes at the faculty.
For going further :
- The Cell Image Library : to have a view of the cells with electron or optic microscope
- Youtube video: an absolutely masterpiece to visualize the cellular operation. We see everything we have just discovered including ribosomes reading a molecule of RNA!