Cells are the smallest units of life and the fundamental components that define living organisms (Corbin, 2017). Due to their extremely small size, they could not be discovered until the invention of the microscope. It was in the 19th and 20th centuries when the cell theory was developed, explaining that cells are the structural units of living beings and stating that all living organisms are composed of one or more cells. They are also considered functional units, as they perform all vital functions (nutrition, relationship, and reproduction). Likewise, cells are genetic units, containing hereditary material, and all originate from another preexisting cell. According to Corbin (2017), prokaryotic and eukaryotic cells are the two main types of cellular life forms, with their division rooted in the trunk of the biological evolution tree.
Cell Classification: Prokaryotes and Eukaryotes
Cells are the structural, functional, and genetic units of all living organisms and can be classified in different ways (Corbin, 2017). Among the main classifications are prokaryotic cells (or prokaryotes) and eukaryotic cells (or eukaryotes). Within eukaryotic cells, one can distinguish between animal and plant cells, as well as those of other eukaryotic organisms such as protozoa, algae, and fungi. The two major groups of cells (prokaryotes and eukaryotes) have similarities and differences. Prokaryotic cells are unicellular organisms that lack a defined cellular nucleus, and the DNA (deoxyribonucleic acid) is dispersed throughout the cytoplasm. According to Corbin (2017), eukaryotic cells are organisms composed of cells that possess a true nucleus, enclosed within a double lipid layer, and with organized cytoplasm.
Cells in Contrast: Eukaryotic and Prokaryotic
Origin
An important difference between prokaryotic and eukaryotic cells lies in the timing of their appearance (Corbin, 2017). Naturally, the first cells were relatively simple, adopting the characteristics of prokaryotic cells. According to Corbin (2017), prokaryotic cells are estimated to have originated approximately 3.7 billion years ago, while eukaryotic cells appeared around 2 billion years ago.
Size and Shape
In general, eukaryotic cells are larger, exceeding 10 micrometers, and exhibit greater complexity compared to prokaryotic cells, which do not exceed 10 micrometers and have a simpler structure (Fernández Roldán, 2023). According to Fernández Roldán (2023), eukaryotic cells can take on various shapes, while prokaryotic cells tend to have a rod or spiral spherical shape.
Cellular Organization
In correspondence with Corbin (2017), prokaryotic cells tend to give rise to unicellular organisms, while eukaryotic cells are responsible for the formation of multicellular organisms, with the genome allowing the emergence of various specialized cells for different biological functions within a living organism.
Nucleus
A fundamental distinction between eukaryotic and prokaryotic cells is related to the cell nucleus, where the cell's DNA is located (Fernández Roldán, 2023). Eukaryotic cells exhibit a clearly defined and easily identifiable nucleus, while prokaryotic cells lack this distinctive feature (Corbin, 2017). According to Corbin (2017), genetic information is stored within the nucleus in eukaryotic cells, whereas in prokaryotes, the genetic material is dispersed throughout the cell's interior, indicating a more primitive and less evolved nature.
Chromosomes
The number of chromosomes is a feature that differentiates the two types of cells: prokaryotic and eukaryotic (Corbin). Corbin (2017) mentions that while prokaryotic cells have a single circular chromosome that houses all their genetic information, eukaryotic cells have multiple linear chromosomes distributed in different regions of the cell nucleus, containing different segments of genetic information.
Genetic Material
Regarding the configuration of genetic material, it is observed that in eukaryotic cells, genetic material is stored in the nucleus (Corbin, 2017). On the other hand, in prokaryotic cells, DNA is dispersed in the cytoplasm. According to Corbin (2017), it is crucial to highlight that in prokaryotic cells, DNA molecules do not associate with histones, which are proteins responsible for the compact structure of genetic material in nucleosomes.
In terms of the shape of genetic material, in prokaryotic cells, genetic information consists of a single circular DNA molecule associated with very few proteins (Brunetti, 2023). Inside the cell, DNA is compacted into a structure called the nucleoid. However, in eukaryotic cells, DNA is organized much more complexly. Genetic material is located in chromosomes, which are composed of a proportional amount of proteins and DNA. Chromosomes are packaged, separated during cell division, transmitted to descendant cells, and transcribed into RNA (ribonucleic acid), which is involved in protein synthesis (Brunetti, 2023). Additionally, according to Corbin (2017), the genetic material of eukaryotic cells is linear and associates with special proteins known as histones.
Cell Membrane
On one hand, in eukaryotic cells, it is observed that cell membranes contain sterols and are composed of phospholipids (Corbin, 2017; Brunetti, 2023). On the other hand, in the case of prokaryotic cells, only mycoplasmas have a cell membrane (Corbin, 2017). In these cells, according to Brunetti (2023), this cell membrane is mainly composed of peptidoglycan or murein.
Organelles
In prokaryotic cells, there is an inner matrix with non-membranous organelles (Corbin, 2017). On the other hand, eukaryotic cells present membranous organelles in the cytoplasm, such as the Golgi apparatus (Corbin, 2017). Moreover, in the cytoplasm of eukaryotic cells, there are several non-membranous structures involved in movement, cell contraction, and the establishment and support of cellular architecture (Brunetti, 2023). These structures are different from those present in prokaryotic cells. That is, the cytoskeleton varies between prokaryotic and eukaryotic cells. While eukaryotic cells have microfilaments, intermediate filaments, and microtubules, in prokaryotic cells, the cytoskeleton is formed by two proteins that seem to be precursors to the proteins in eukaryotic cells. The main difference, according to Brunetti (2023), is that these proteins in prokaryotic cells do not cluster to form microtubules in the cytoskeleton.
Reproduction
Another fundamental distinction between eukaryotic and prokaryotic cells is in relation to reproduction (Fernández Roldán, 2023). In prokaryotic cells, reproduction takes place through the process of binary fission as a method of asexual reproduction (Corbin, 2017). On the contrary, according to Corbin (2017), in eukaryotic cells, reproduction occurs through mitosis and meiosis.
Types of Living Organisms They Give Rise To
The lifestyle as independent unicellular organisms is characteristic of prokaryotic cells (Fernández Roldán, 2023). Within eukaryotic cells, some live in a unicellular and free form, while others constitute complex multicellular organisms (Fernández Roldán, 2023). According to Corbin (2017), bacteria represent the group of prokaryotic cells, while eukaryotic cells are divided into animals, plants, fungi, protozoa, and algae.
Beyond the Differences
Prokaryotic cells and eukaryotic cells, although different in many aspects, also exhibit certain similarities (Corbin, 2017). Both are the basic and fundamental units of life on Earth, and thanks to them, different unicellular and multicellular organisms have been able to evolve and colonize various habitats on the planet (Fernández Roldán, 2023). According to Fernández Roldán (2023), both are characterized as membrane-bound structures that preserve their DNA or genetic information inside, along with different enzymatic machinery that enables them to carry out essential functions of nutrition, growth, and reproduction.
Their basic chemical structures are similar, as they are composed of carbohydrates, proteins, nucleic acid, minerals, fats, and vitamins (Corbin, 2017). Additionally, both prokaryotic and eukaryotic cells contain ribosomes (which produce proteins), regulate the flow of nutrients and waste entering and leaving the cells, reproduce (though in different ways), require energy to survive, contain cytoplasm inside, and have a cytoskeleton (Corbin, 2017). Finally, in accordance with Corbin (2017), both cell types have a lipid bilayer known as the plasma membrane, which forms the boundary between the inner and outer sides of the cell.
References
Brunetti, A. (2023, enero 29). Diferencias Entre la Célula Eucariota y Procariota. Ciencia y Biología. https://cienciaybiologia.com/diferencias-celula-eucariota-procariota/
Fernández Roldán, L. (2023, mayo 18). Diferencia Entre Célula Eucariota y Procariota. Ecologia Verde. https://www.ecologiaverde.com/diferencia-entre-celula-eucariota-y-procariota-2550.html
Páez, J. C. (2021, marzo 1). Partes de la Célula Animal. Ecología Verde. https://www.ecologiaverde.com/partes-de-la-celula-animal-3279.html
Corbin, J. A. (2017, septiembre 1). Las 12 Diferencias Entre Célula Eucariota y Célula Procariota. Psicología y Mente. https://psicologiaymente.com/cultura/diferencias-celula-eucariota-procariota
