The eukaryotic cell is the building block of life in protozoa, fungi, plants, and animals. It represents the fundamental biological basis of the organisms belonging to the Eukarya domain.
The word “eukaryotic” is derived from the Greek eukaryon ( eu (true) + karyon(nucleus)) which means true nucleus.
Differences between prokaryotic cell and eukaryotic cell
Within the concept of cells, we know that there are two types: prokaryotic and eukaryotic. The prokaryotic cell is a simple structure, with its genetic material and its free components in the cytoplasm. In contrast, the eukaryotic cell presents more elaborate compartments and functions. In addition, many types of eukaryotic cells can form a multicellular organism.
In the eukaryotic cell, the genetic material is sheltered in an internal membranous structure, called the nucleus. From here begin the activities aimed at cell division and protein synthesis.
Structure of the eukaryotic cell
In every eukaryotic cell, three main parts can be distinguished:
- The plasma membrane: the envelope that contains all the cellular material, besides being the means by which cells exchange information, receive nutrients and eliminate waste.
- The core: is the center of control and regulation of cellular functions. It is made up of the nuclear envelope and the nuclear content.
- The cytoplasm: is the aqueous-gelatinous space in which the cellular elements float and their activities develop.
Characteristics of the eukaryotic cell
The distinctive feature of all eukaryotic cells is the presence of the nucleus. However, there are other characteristics:
- They have varied forms: from spherical and cylindrical, to flat and cubic. The shape of a cell is not fixed, it depends on the medium in which it is located. For example, the cells of the epidermis, the superficial layer of the skin, are cuboidal initially and as they age they become flat.
- They have varied sizes: they can range from 10 μm to 100 μm. In order to observe these cells, a microscope is required. However, there are some cases of cells that can be observed with the naked eye, such as frog eggs (1 mm) and eggs of birds.
- They have organelles: in addition to the nucleus, eukaryotic cells contain many other types of organelles, which may include mitochondria, chloroplast, Golgi apparatus, among others. Each organelle is separated from the rest of the cell space by a membrane as if it were the rooms inside a house.
- The functions are separate: The functions that a eukaryotic cell must carry out are separated in the organelles. For example, the chloroplast is responsible for photosynthesis, the mitochondrion is responsible for cellular respiration, the Golgi apparatus is responsible for the packaging of material.
- Internal structural framework: the cytoskeleton of the eukaryotic cell is composed of filamentous proteins that give physical support to the cell and the constituents of the cytoplasm.
Why is the nucleus of the eukaryotic cell so important?
The presence of the nucleus is distinctive of the eukaryotic cell. This structure is so important because it is the place where the DNA of the cell is lodged, that is, where the genetic information is located. It is also the place where the process of synthesis of proteins begins, which are the effectors of the different cellular activities.
For the synthesis of proteins, first, the DNA is “rewritten” in a type of RNA, called a messenger. This messenger RNA leaves the nucleus towards the ribosomes, where the genetic information is transformed into protein. By separating the DNA from the rest of the cellular components, protein production is improved.
Origin of the eukaryotic cell
The origin of the eukaryotic cell is a subject of wide discussion in biology. According to fossil records, eukaryotic beings emerged 2 billion years after the prokaryotes.
According to this model, the prokaryotic cell itself evolved creating internal structures from its own plasma membrane, which then specialized in organelles, originating the eukaryotic cell.
Lynn Margulis (1938-2011) suggested in 1967 that the first step in the origin of eukaryotes was the need to survive in an oxygen-rich environment. Therefore, an aerobic prokaryote (the protomitochondria) was ingested by an anaerobic prokaryote. Then the first endosymbiosis was formed on Earth, by combining the DNA of both microorganisms. This theory is known as the Endosymbiotic Theory.
Examples of eukaryotic cells
Within each of the kingdoms that make up the Eukarya domain, we have different examples of eukaryotic cells. Similarly, within our organization, we have a huge diversity of cells with specialized functions. Let’s see some examples.
Protozoa are unicellular, eukaryotic, heterotrophic organisms that can live freely or be parasites. For example, Leishmania donovani is the causative agent of leishmaniasis, a disease that affects humans and can also affect dogs. The protozoan Dileptus sp. is a heterotrophic unicellular ciliate with a large trunk (or proboscide) that lives in an aquatic environment.
Mosses are bryophyte plants, that is, seedless plants without internal circulatory vessels, which grow mainly on the trunks of trees.
The algae are eukaryotic organisms belonging to the Plantae kingdom, which can be unicellular or multicellular. Like plants, they have chlorophyll and are autotrophic, thanks to the process of photosynthesis.
The plants are autotrophic eukaryotic organisms. Inside the plant, cells are the chloroplasts, organelles with chlorophyll responsible for the process of photosynthesis. They also have a cell wall, which is an external structure to the plasma membrane, which gives it greater support.
Within the Eukarya domain is the Fungi kingdom that encompasses all fungi, yeasts, and mold. Yeasts are the unicellular organisms within this kingdom.
For example, Saccharomyces cerevisiae is the yeast of bread and wine, Pichia pastoris is used in biotechnology and Candida albicans is the causative agent of many fungal infections in humans.
Neurons are specialized cells in the transmission of nervous impulses. They are characterized by having a cell body, from which arise several short ramifications, dendrite flames, and a long membranous branch or tube, known as an axon.
The megakaryocyte is a giant cell that is found in the bone marrow (inside the bones). It is an interesting cell because when it reaches maturity it fragments into dozens of pieces that we know as platelets. Platelets are important in the process of coagulation and tissue repair in mammals.
Human Megacariocyte at the moment it breaks into pieces and each of these forms the platelets.
8. Red blood cells or erythrocytes
Red blood cells or erythrocytes are a type of special eukaryotic cell. Why? Because they have no nucleus! In the process of maturation of red blood cells in the bone marrow of mammals, they lose the nucleus and leave to the blood with the form that we know them. Therefore, red blood cells can not be divided and only survive in the human circulation for approximately 120 days.
HeLa cells are a cell line widely used in scientific research. They are called that because they were taken from Henrietta Lacks in 1951, a woman who died of cancer. These cells are “immortal”, that is, they can be divided as many times as they want when they are maintained in cell culture.
10. Stem cells
Stem cells are those cells of a superior multicellular organism that has the ability to form all cells. For example, in the embryo, which is the initial stage of an animal’s formation, the first cells that form are divided several times, to then form the cells of the extremities, the eyes, the heart, and the brain.