Cells are significant units for the life of every being living on Earth —including bacteria, parasites, and fungi. There are two main cell types: prokaryotes and eukaryotes.
In this article, we will explain what cells are and the main differences between eukaryotes and prokaryotes.
Cells are the morphological and functional unit that make up every living being. All living organisms are composed of at least one. Most animal cells have sizes from 10 to 100 micrometers and have several key elements.
The most complex organisms, such as mammals, are composed of an enormous set of these vital units that work coordinately. They have different specialized parts to develop and carry out particular functions.
The human body is composed of more than 200 types of cells, each specialized in a specific function such as memory, sight, movement, or digestion, among many others. The diversity within the different cell types is really extensive.
Cell biology is a branch of biology that studies the different types of cells. The knowledge and basic information that has been discovered about this type of organism have also been extrapolated to other different ones over time.
The origin of the first cell
According to researchers, the first life emerged about 3,8 billion years ago, or 750 million years after the Earth formed. It is speculated that the first cell arose from the RNA envelope of self-replication in a membrane composed of phospholipids.
The self-replicating RNA envelope and the molecules associated with a lipid membrane have therefore been maintained as a unit capable of reproducing itself and evolving over time. The synthesis of proteins from RNA may already have evolved.
Cells can be divided into two main classes: prokaryotes (or bacteria) and eukaryotes. Prokaryotes were the first organisms to evolve on Earth, preceding eukaryotes in the fossil record in approximately 1 billion years.
The first prokaryotes were probably bacteria that performed photosynthesis (cyanobacteria), which is a process that produces carbohydrates from sunlight, water, and carbon dioxide. It is also believed that eukaryotes evolved when they encompassed prokaryotes and incorporated them into their cytoplasm.
The two types differ in several important respects. Below are the most important characteristics of these two types of vital units.
First, prokaryotic cells lack a nuclear envelope, and eukaryotic cells have a nucleus where the genetic material is separated from the cytoplasm. Likewise, eukaryotes are more complex and highly organized than prokaryotes.
Also, eukaryotes are, on average, ten times larger. Only eukaryotes have organelles attached to the membrane. These organelles are separated from the cytoplasm by plasma membranes.
In the eukaryotic units, the DNA is contained within a nucleus, an organelle joined by a double membrane. Eukaryotic DNA is linear, with a beginning and an end, and is divided into a series of separate chromosomes. Prokaryotes, on the other hand, have a single circular chromosome, some DNA that is not contained in a nucleus.
A big difference between the two types is that eukaryotes can have much larger amounts of DNA, which is necessary for the evolution of complex organisms.
Prokaryotes are unicellular organisms, such as bacteria that do not have a distinct nucleus. They also lack many other small organelles found in larger eukaryotic cells.
These organelles found in eukaryotes include mitochondria, which are responsible for cell metabolism —the conversion of food into usable energy resources in the form of ATP— and chloroplasts, which allow species involved in photosynthesis to use light energy to fix carbon. While both functions are also performed by prokaryotes, the machinery for these processes is not organized into organelles.
Finally, in eukaryotic cells we also find other organelles such as the endoplasmic reticulum —responsible for protein synthesis— and the Golgi apparatus —responsible for processing and packaging of endoplasmic reticulum proteins—, which are not found in prokaryotic cells.
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