In a recent article we defined life as both a useful work and a useful assimilation process and concluded that the natural structure that is able to host and allow life on earth is the biological cell. Then, if we want to really know what life is beyond the mere definition we need to know the biological cell and how it does to do that useful work usually called life. In this article we will not only present the cell and its functioning but also describe life in its simplest form so to give you an idea of what life is all about.
What is a cell, a living cell?
Anybody can Google the word cell or biological cell to have definitions and images of what such cell look like. Here are my definition and description of a biological cell:
A living cell is the simplest organization of matter that is able to host and allow life that I defined as a useful work or a useful assimilation.
The cell is the simplest living organism you can find on earth. It is also the fundamental active unit making up more complex living organisms. In other words, living organisms are single cells or more or less organized societies of cells.
Otherwise living organisms are just cell organisms. On this earth, what is able to host and do the complex task that is called life has at least one living cell at the base of its structure and its functioning.
How does a cell look like?
A cell can take different forms but basically it has a oval form and resembles a balloon. It has two distinctive parts but can be described as having three parts when we take into account how it functions to achieve the useful work that is life.
A cell has an external part that is an envelope that is the equivalent of our skin holding the cell content together. It is more practical to call it the Cell envelope because it may have one, two or even three layers according to the cell nature. But it always has a fundamental layer called the cell membrane that can be single or covered externally with one or two layers The cell envelop defines the cell, protects it and at the same time allows the cell to exchange matter/energy with its environment.
The content of the cell envelop, the body of the cell is called the cytoplasm made of at least 70% of a liquid phase called hyaloplasm (salt water rich in organic molecules such as proteins, fats or lipids, sugars or carbohydrates, RNA, etc.) containing organelles (ribosomes, reticulum, dictyosomes, mitochondria, plastids, vacuoles, etc. Among the organic molecules it is important to know that an important portion of proteins are enzymes that are active elements transforming living matter/energy continually, through chemicals reactions they catalyze and that are the basic cell activities making up the whole complex phenomenon called life..
We may then say that a living cell has two parts; a cell envelop and a cytoplasm. But in the cytoplasm there is a place for the genetic material called DNA that interact with the cytoplasm to sustain life and that needs to be set apart because of that. We call it the Genetic center because it may take one of the two forms:
- In the simplest cells called Prokaryotic organisms (bacteria, blue-green algae, mycoplams
- ), the genetic center is made of a circular molecule of naked DNA in a place deprived of ribosomes and called the nucleoid.
- In more recent and more complex cell the genetic center is the well known nucleus that have an envelope of its own containing linear molecules of DNA each coated in a protein structure making up linear chromosomes found in animals, plants eukaryotic unicellular organisms called protists..
So a cell can be described as having three parts: a cell envelop, a cytoplasm (hyaloplasm and organelles) and a genetic center ( a nucleoid or a nucleus).