- What is a eukaryotic cell?
- Eukaryotic cell types
- Eukaryotic cell functions
- Parts of a eukaryotic cell
- Difference between eukaryotic cell and prokaryotic cell
We explain what a eukaryotic cell is, the types that exist, their parts and functions. Also, its differences with a prokaryotic cell.
What is a eukaryotic cell?
It is called a eukaryotic cell (from the Greek word eukaryota, binding of eu "True" and karyon "Nut, nucleus") to all those cells in whose cytoplasms a membrane can be found that delimits the cell nucleus, which contains most of their genetic material (DNA). In this it differs from prokaryotic cell, much more primitive and whose genetic material is dispersed in the cytoplasm. Furthermore, unlike prokaryotes, eukaryotic cells possess organelles or organelles, specialized subcellular structures that can be identified within and are delimited by membranes (for example, cells mitochondria and chloroplasts).
The emergence of eukaryotic cells was an important step in the evolution of life, laying the foundation for much greater biological diversity, including the emergence of cells specialized within multicellular organizations. This gave rise to the kingdoms: protists, mushrooms, plants, Y animals. The living beings made up of eukaryotic cells are called eukaryotes.
Although the scientific community does not doubt about the relevance of the appearance of eukaryotic cells, it has not yet been possible to give a very clear explanation of their emergence. The most accepted theory raises the possible symbiogenesis between two prokaryotes, that is, a process of symbiosis between one bacterium and an archea that, coexisting in a very close way, would have composed the same organism with the passing of the generations, so dependent that they became one on the other. This theory about the emergence of eukaryotic cells was raised by the American evolutionary biologist Lynn Margulis in 1967, and is known as "Endosymbiotic Theory" or "Serial Endosymbiosis Theory".
Eukaryotic cell types
There are various types of eukaryotic cells, but fundamentally four are recognized, each with different structures and processes:
- Vegetables cells. They have a cell wall (composed of cellulose and protein) that covers your plasma membrane and gives them rigidity, protection and resistance. In addition, plant cells have chloroplasts, that is, organelles that contain the necessary chlorophyll to carry out the process of photosynthesis; and a large central vacuole, which maintains cell shape and controls the movement of the molecules in the cytoplasm.
- Animal cells. They do not have chloroplasts (since they do not photosynthesize) or a cell wall. But, unlike plant cells, they have centrioles (organelles that participate in cell division) and have smaller but more abundant vacuoles, called vesicles. Due to the lack of a cell wall, animal cells can take a large number of variable forms, and even engulf other cells.
- Fungi cells. They resemble animal cells, although they differ from them by the presence of a cell wall composed of chitin (which animal cells do not have). Another distinguishing feature is that fungal cells have less cell specialization than animal cells. Although it is not the most frequent, there are unicellular fungi, such as yeast.
- Protist cells. Eukaryotic cells are often part of multicellular organisms. However, there are protists that are simple unicellular or multicellular eukaryotic organisms that do not form tissues. Although unicellular eukaryotes are simpler beings than animals and plants, the fact of being made up of a single cell that has to carry out all the functions of the organism makes the cell have a complex organization. In addition, they can reach macroscopic sizes. Some examples of this type of organisms are the euglena and the paramecia.
Eukaryotic cell functions
Eukaryotic cells have two primary functions: feeding and reproducing.
Eukaryotic cells, like prokaryotes, carry out essential functions:
- Nutrition. It includes the incorporation of nutrients into the interior of the cell and their transformation into other substances, which are used to form and replace cell structures and also to obtain the Energy necessary to carry out all its functions. Depending on their nutrition, cells can be autotrophs (they make their own food from inorganic material by processes such as photosynthesis) or heterotrophs (they must incorporate the organic material because they are not capable of manufacturing it). The sum of all the chemical activities of the cell is its metabolism.
- Increase. It involves an increase in the size of individual cells in an organism, in the number of cells, or in both. Growth can be uniform in various parts of an organism or it can be greater in some parts than others, causing the body's proportions to change as growth occurs.
- Response to stimuli. Cells interact with the environment that surrounds them, receiving different stimuli (such as variations in temperature, humidity or acidity) and elaborating the corresponding responses to each of them (such as contraction or translation). This ability to react to environmental stimuli is known as irritability.
- Reproduction. It is the process of formation of new cells (or daughter cells) from an initial cell (or stem cell). There are two types of cell reproduction processes: mitosis Y meiosis. Through mitosis, a stem cell gives rise to two identical daughter cells, that is, with the same amount of genetic material and identical hereditary information. On the other hand, through meiosis, a stem cell gives rise to four daughter cells that are genetically different from each other and which also have half the genetic material of the initial cell. Mitosis intervenes in the processes of tissue growth and repair, and in the reproduction of living beings that reproduce asexually. Meiosis has another objective: it only occurs to give rise to gametes.
- Adaptation. The ability of cells to evolve over many generations and adapt to their environment enables them to survive in a changing world. Adaptations are inherited characteristics that increase an organism's ability to survive in a particular environment. The adaptations can be structural, physiological, biochemical, behavioral, or a combination of the four. All biologically successful organisms are a complex collection of coordinated adaptations that have occurred through evolutionary processes.
The functions of metabolism, growth, response to stimuli, reproduction and adaptation are carried out by all cells belonging to both prokaryotic and eukaryotic organisms. However, these are not the only cellular functions: there are other functions depending on each type of cell and the tissue or organism to which they belong. For example, neurons (which are part of the nervous tissue) are able to communicate through electrical impulses.
Parts of a eukaryotic cell
The main components of eukaryotic cells are:
- Cell or plasma membrane. It is a double barrier composed of lipids Y protein that delimits the cell, to isolate it from the environment that surrounds it. The plasma membrane has selective permeability: it allows only the entry of substances necessary to the cytoplasm and also the expulsion of metabolic waste. This structure is present in all eukaryotic cells and even in prokaryotes.
- Cellular wall. It is a rigid structure that is outside the plasma membrane and gives the cell shape, support and protection. The cell wall is present only in the vegetables cells and in fungi, although its composition varies between both cell types: in plants it is made up of cellulose and proteins, while in fungi it is made up of chitin. Although this structure protects the cell, it prevents its growth and limits it to fixed structures.
- Cell nucleus. It is a central organelle, limited by a double porous membrane that allows the exchange of material between the cytoplasm and its interior. The nucleus houses the genetic material (DNA) of the cell, which is organized into chromosomes. In addition, within the nucleus there is a specialized region called the nucleolus, where the ribosomal RNA is transcribed, which will later become part of the ribosomes. The nucleus is present in all eukaryotic cells.
- Ribosomes. They are structures formed by RNA and proteins, in which protein synthesis takes place. Ribosomes are found in all types of cells, even prokaryotes (although they are minor). Some ribosomes are free in the cytoplasm and others are attached to the rough endoplasmic reticulum.
- Cytoplasm. It is the aqueous medium in which the different organelles of the cell are. The cytoplasm is made up of the cytosol, the organelle-free aqueous part that contains dissolved substances, and the cytoskeleton, a network of filaments that gives shape to the cell.
In addition to the presence of the nucleus, one of the distinctive characteristics of the eukaryotic cell is the presence of organelles or subcellular compartments surrounded by a membrane, which have specialized functions. Some are:
- Lysosomes. They are vesicles filled with enzymes digestive systems, present exclusively in animal cells. Cellular digestion processes are carried out in lysosomes, catalyzed by the enzymes they contain within.
- Mitochondria. They are the organelles where the process of cellular respiration. They are surrounded by a double membrane, which allows the cell to obtain the energy it needs to carry out its functions. Mitochondria are present in all types of eukaryotic cells and their number varies depending on their needs: cells with high energy requirements tend to have a greater number of mitochondria.
- Chloroplasts They are the organelles in which photosynthesis takes place, and they present a complex system of membranes. The fundamental component of these organelles is chlorophyll, a green pigment that participates in the photosynthetic process and allows it to capture the sunlight. Chloroplasts are unique to photosynthetic cells, so they are present in all plants and algae, whose color Characteristic green is given by the presence of chlorophyll.
- Vacuole. They are a type of large gallbladder that stores Water, mineral salts and other substances, and which are only found in plant cells. The vacuole maintains cell shape and provides support to the cell, in addition to participating in the intracellular movement of substances. Animal cells have vacuoles but they are smaller and in greater quantity.
- Centrioles. They are tubular structures found exclusively in animal cells. They participate in the separation of chromosomes during the process of cell division.
- Endoplasmic reticulum. It is a membrane system that continues with the cell nucleus and extends throughout the cell. Its function is related to the synthesis of compounds destined mainly for the exterior of the cell. The endoplasmic reticulum is divided into rough and smooth, depending on the presence or absence of ribosomes on its surface: the rough reticulum contains ribosomes and is mainly responsible for the synthesis of proteins for export, while the smooth reticulum is mainly related to metabolic pathways of the lipids.
- Golgi apparatus. It is an organelle made up of a set of flattened discs and sacs called cisterns. The function of the Golgi apparatus is related to the modification and packaging of proteins and other biomolecules (as carbohydrates and lipids) for secretion or transport.
Difference between eukaryotic cell and prokaryotic cell
The main differences between these two types of cells are:
- Core presence. The most important difference is that in prokaryotes the genetic material is dispersed in the cytoplasm in a region called the nucleoid, instead of within the nucleus, as is the case in eukaryotes.
- DNA type. Prokaryotes have a single, circular DNA molecule, which is not associated with proteins, which is why it is often referred to as "naked, circular DNA." For its part, the genetic material of eukaryotes has a linear shape and is associated with proteins, forming chromatin (or chromosomes, when the cell is about to enter cell division). Each species of eukaryotic organism has a characteristic number of chromosomes.
- Size. Eukaryotic cells are considerably larger in size (10-100 µm) than common prokaryotic cells (0.2-2.0 µm).
- Constitution. Most eukaryotic organisms are multicellular, while all prokaryotes are unicellular. However, it is worth remembering that there are some unicellular eukaryotic organisms, such as paramecia and yeast.
- Reproduction. Prokaryotes reproduce asexually (by binary fission), while eukaryotes have both sexual reproduction (by meiosis, giving rise to gametes or sex cells) as asexual (for mitosis).
- Cellular organelles. Eukaryotic cells present organelles with specific membranes and functions, such as mitochondria, lysosomes or chloroplasts.