Eukaryotic Cell: Definition, Structure Types, Examples, Functions, Characteristics
Introduction to Eukaryotic Cell
Eukaryotic cells are the structural components of a broad lineage of organisms characterized by cells with a membrane-bound nucleus and having a set of organelles. Among the most prominent organelles of eukaryotes, we have the mitochondria, responsible for cellular respiration and other pathways related to energy generation and chloroplasts, found in plants and responsible for the photosynthetic process.
In addition, there are other structures limited by membranes such as the Golgi apparatus, the endoplasmic reticulum, vacuoles, lysosomes, peroxisomes, among others, that are unique to eukaryotes.
The organisms that are part of the eukaryotes are quite heterogeneous, both in size and morphology. The group ranges from single-celled protozoa and microscopic yeasts to plants and large animals that inhabit the deep sea.
Eukaryotes differ from prokaryotes mainly by the presence of the nucleus and other internal organelles, in addition to having a high organization of genetic material. It can be said that eukaryotes are much more complex in different aspects, both structural and functional.
Eukaryotic Cell Definition
The name of eukaryotic cells comes from ancient Greek and its meaning is “true walnut”, this term refers to the presence of a defined nucleus covered by a cell membrane.
The Cell which has Developed Nucleus is called Eukaryotic Cell
Origin of the eukaryotic cell
- The emergence of eukaryotic cells occurred at some point in evolutionary cellular history when only much simpler and smaller prokaryotic unicellular organisms existed.
- It is not known for sure how this leap into cellular structural complexity occurred or without which life had been reduced to single-cell colonies.
- There are various theories. The most accepted one proposes the origin of these cells in the symbiogenesis between two prokaryotes: a bacterium and archaea.
- Both would have cohabited so closely that they ended up composing the same organism, with a higher level of complexity.
General characteristics of Eukaryotes
The most important characteristics that define a eukaryotic cell are the presence of a nucleus defined with the genetic material (DNA) inside, the subcellular organelles that perform specific tasks, and the cytoskeleton.
Thus, some lineages have special characteristics. For example, plants have chloroplasts, a large vacuole, and a thick cellulose wall. In fungi, the chitin wall is characteristic. Finally, animal cells have centrioles.
Similarly, eukaryotic unicellular organisms exist within protists and fungi.
Structure of Eukaryotic cell
One of the distinctive characteristics of eukaryotes is the presence of organelles or subcellular compartments surrounded by membranes. Among the most conspicuous we have:
The nucleus is the most conspicuous structure in eukaryotic cells. It is delimited by a double porous lipid membrane that allows the exchange of substances between the cytoplasm and the nuclear interior.
It is the organelle in charge of coordinating all the cellular processes since it contains all the necessary instructions in the DNA that allow it to carry out an immense variety of processes.
The nucleus is not a perfectly spherical and static organelle with DNA scattered randomly within it. It is a structure of exquisite complexity with different components such as the nuclear envelope, the chromatin, and the nucleolus.
There are also other bodies inside the nucleus such as the Cajal bodies and the PML bodies (promyelocytic leukemia)
Read More: Nucleus
Mitochondria are organelles surrounded by a double membrane system and are found in both plants and animals. The number of mitochondria per cell varies according to its needs: in cells with high energy requirements, the number is relatively higher. The metabolic pathways that take place in the mitochondria are the citric acid cycle, electronic transport, oxidative phosphorylation, beta-oxidation of fatty acids, and breakdown of amino acids.
Read More: Mitochondria
Chloroplasts are typical plant and algae organelles, which have complex membrane systems. The most important constitute is chlorophyll, a green pigment that participates directly in photosynthesis.
In addition to the reactions associated with photosynthesis, chloroplasts can generate ATP, synthesize amino acids, fatty acids, among others. Recent studies have shown that this compartment is related to the production of substances against pathogens.
Like mitochondria, chloroplasts have their own genetic material, in a circular shape. From an evolutionary point of view, this fact is evidence that supports the theory of the possible endosymbiotic process that gave rise to mitochondria and chloroplasts.
The reticulum is a system of membranes that continues with the nucleus and that extends throughout the cell in the form of a net. It is divided into a smooth endoplasmic reticulum (SER) and a rough endoplasmic reticulum (RER), depending on the presence of ribosomes in it. The rough endoplasmic reticulum is primarily responsible for protein synthesis – thanks to anchored ribosomes. on the other hand, SER is related to the metabolic pathways of lipids.
Read More: Endoplasmic Reticulum
It consists of a series of flattened discs called “Golgian cisterns”. It is related to the secretion and modification of proteins. It also participates in the synthesis of other biomolecules, such as lipids and carbohydrates. It is responsible for modifying proteins and lipids and packaging them in vesicles for secretion or transport.
Ribosomes are corpuscles in which proteins are made. They are responsible for binding amino acids in a precise sequence to make a specific protein. RNA plays an important role when it comes to conjugating proteins. Its main job is to gather and encode the information that genes provide us, through the same DNA. It is the same RNA that subtracts the information from the enzymes and sends one of the ribosomes out of the nucleus. This will then be used to synthesize and conjugate the proteins. Ribosomes are also present in prokaryotic cells
Read More: Ribosome
Vesicles: structures that store and transport substances, some are also responsible for degrading them.
Endosomes and lysosomes
Endosomes are organelles functionally located between the Golgi apparatus and the cytoplasmic membrane. They are vesicles of varied shapes and dimensions, although they are generally small.
Endosomes receive vesicles from the Golgi apparatus (which generally carry hydrolytic enzymes) and vesicles from the cytoplasmic membrane (which carry macromolecules from outside). Once the endosome joins both vesicles, the lysosome forms from these. Lysosomes are responsible for digesting the materials entered by endocytosis and also for digesting elements from the cell itself. The shape and composition of lysosomes are highly variable, depending on the combination of hydrolytic enzymes they contain.
Read More: Lysosome
Vacuoles: type of vesicle present in plant cells, large. Stores water, mineral salts, and other nutrients. Keeps fit and supports the cell. A vacuole is a large vesicle surrounded by a membrane called a tonoplast. They are typical organelles of plant cells, their number is variable, there may be one large vacuole or several of different sizes. It originates from the fusion of vesicles from the Golgi apparatus. Vacuoles perform several functions:
They store nutrients, such as the storage of reserve proteins from many seeds; or toxic waste products. They store pigments like those that give color to flower petals.
They accumulate water that is used to regulate the volume and turgor of the cell. The increase in the size of plant cells is largely due to the accumulation of water in their vacuoles, which is a very economical system for the growth of plant cells.
They function as lysosomes since they contain hydrolytic enzymes.
Peroxisomes: type of vesicle that breaks down substances, especially fatty acids, and other toxic substances, through oxidative enzymes.
Centrioles: found in animal cells, usually in pairs. They are tubular structures from which the microtubules that form the cytoskeleton emerge. They also participate in the separation of chromosomes during cell division. The centriole, which is found only in the eukaryotic animal cell, plays an important role in cell reproduction or division.
The centrioles are also in charge of controlling the small fibers that separate the chromosomes, this is done when the cells divide and thus each of the new ones receives the correct information from the genes. They are cylindrical in shape and have 9 sets of 3 microtubules, each of them.
Types of Eukaryotic organisms / Examples of Eukaryotic Cell
In 1980, researcher Carl Woese and collaborators managed to establish relationships between living things using molecular techniques. Through a series of pioneering experiments, they managed to establish three domains (also called “super kingdoms”) leaving behind the traditional view of the five kingdoms.
Read: Kingdom Animalia
According to Woese’s results, we can classify the living forms of the earth into three conspicuous groups: Archaea, Eubacteria, and Eukarya. In the Eukarya domain are the organisms that we know as eukaryotes. This lineage is widely diverse and encompasses a series of organisms both unicellular and multicellular.
- Single-celled eukaryotes are highly complex organisms since they must possess in one cell all the typical functions of a eukaryote. Protozoa are historically classified as rhizopods, ciliates, flagellates, and sporozoans.
- As more outstanding examples we have the Euglena: photosynthetic species capable of moving using a flagellum.
- There are also ciliated eukaryotes, such as the famous paramecia belonging to the genus Paramecium.
- These present a typical shoe shape and move thanks to the presence of numerous cilia.
- In this group, there are also pathogenic species of humans and other animals, such as the genus Trypanosoma.
- This group of parasites is characterized by having an elongated body and a typical flagellum. They are the cause of Chagas disease (Trypanosoma cruzi) and sleeping sickness (Trypanosoma brucei).
- The Plasmodium genus is the causative agent of malaria or malaria in humans. This disease can be fatal.
- Unicellular fungi also exist, but the most outstanding characteristics of this group will be described in later sections.
- All the great complexity of plants that we observe daily belongs to the eukaryotic lineage, from grasses and grasses to complexes and large trees.
- The cells of these individuals are characterized by having a cell wall composed of cellulose, which stiffens the structure.
- In addition, they have chloroplasts that contain all the biochemical elements necessary for the photosynthetic process to occur.
- Plants represent a highly diverse group of organisms, with complex life cycles that would be impossible to encompass a few characteristics.
Read : Plant Cell Structure & Functions
Fungi / Mushrooms
- The term “fungus” is used to designate different organisms such as molds, yeasts, and individuals that are capable of producing mushrooms.
- Depending on the species, they can reproduce sexually or asexually.
- They are mainly characterized by the production of spores: small latent structures that can develop when the environmental conditions are adequate.
- You might think that they are similar to plants since both are characterized by leading a sessile way of life, that is, they do not move.
- However, fungi lack chloroplasts and do not have the enzymatic machinery necessary to perform photosynthesis.
- Their diet is heterotrophic, like most animals, so they must find a source of energy.
- Animals represent a group made up of almost a million species cataloged and classified correctly, although zoologists estimate that the real value could be close to 7 or 8 million. They are as diverse a group as those mentioned above.
- They are characterized by being heterotrophs (they look for their own food) and they have remarkable mobility that allows them to move.
- For this task, they have a series of various locomotion mechanisms that allow them to move on land, water, and air.
- Regarding its morphology, we find incredibly heterogeneous groups.
- Although we could make a division into invertebrates and vertebrates, where the characteristic that distinguishes them is the presence of the vertebral column and the notochord.
- Within the invertebrates, we have the Porifera, cnidarians, annelids, nematodes, flatworms, arthropods, mollusks, and echinoderms.
- While vertebrates include better-known groups such as fish, amphibians, reptiles, birds, and mammals.
Examples of Eukaryotic cell
There is a great diversity of eukaryotic cells. Although one might think that the most complex is found in animals and plants, this is incorrect. The greatest complexity is observed in protist organisms, which must have all the elements required for a life confined within a single cell.
The evolutionary pathway that led to the appearance of multicellular organisms brought with it the need to distribute tasks within the individual, which is known as cell differentiation. Thus, each cell is in charge of a series of limited activities and has a morphology that allows it to carry it out.
When the gamete fusion or fertilization process occurs, the resulting zygote undergoes a series of subsequent cell divisions that will lead to the formation of more than 250 cell types.
In animals, the differentiation pathways followed by the embryo are directed by signals it receives from the environment and largely depend on its position in the developing organism. Among the most outstanding cell types we have:
The neurons or cells specialized in the conduction of the nervous impulse that is part of the nervous system.
Skeletal muscle cells have contractile properties and are aligned in a network of filaments. These allow the typical movements of animals such as running or walking.
Cartilage cells specialize in support. For this reason, they are surrounded by a matrix that presents collagen.
The cellular components of blood are red and white blood cells and platelets. The former has a disk shape, lacks a nucleus when they are mature, and has the function of transporting hemoglobin. White blood cells participate in the immune response and platelets in the blood clotting process.
Eukaryotes have a series of metabolic pathways such as glycolysis, pentose phosphate pathways, beta fatty acid oxidation, among others, organized in specific cellular compartments. For example, ATP is generated in the mitochondria.
Characteristics of Plant cells
- characteristic metabolism, since they have the enzymatic machinery necessary to take sunlight and generate organic compounds.
- This process is photosynthesis and converts them into autotrophic organisms that can synthesize the energy components required by their metabolism.
- Plants have a specific pathway called the glyoxylate cycle that occurs in the glyoxysome and is responsible for converting lipids to carbohydrates.
- Animals and fungi are characterized by being heterotrophic. These lineages are not capable of producing their own food, so they must actively seek and degrade it.
Eukaryotic cell functions
- First of all, before entering an enumeration, it must be said that eukaryotic cells are the product of evolution, are the ones that allow beings that exist beyond prokaryotic bacteria today and for a long time.
- But in the specificity of its function, we have to say that it controls the exchange between the cell itself and its environment,
- it contains DNA (the hereditary information),
- it produces and transports fats and proteins from inside and outside,
- it performs secretion and division cell, produce and destroy hydrogen peroxide,
- store nutrients, expectorate waste; at the vegetable level, it is in charge of photosynthesis, etc.
Differences between prokaryotes and eukaryotes
The crucial difference between a eukaryote and a prokaryote is the presence of a nucleus bounded by a membrane and defined in the first group of organisms.
We can reach this conclusion by examining the etymology of both terms: prokaryote comes from the roots pro which means “before” and karyon which is the nucleus; while eukaryote refers to the presence of a “true nucleus” (EU which means “true” and karyon which means nucleus)
However, we find single-celled eukaryotes (that is, the entire organism is a single cell) such as the well-known Paramecium or yeast. Similarly, we find multicellular eukaryotic organisms (made up of more than one cell) like animals, including humans.
Read: prokaryotic Cell
According to the fossil record, it has been possible to conclude that eukaryotes evolved from prokaryotes. Therefore, it is logical to assume that both groups have similar characteristics such as the presence of cell membranes, common metabolic pathways, among others. The most conspicuous differences between the two groups will be described below:
In prokaryotic organisms, there are no structures delimited by a cell membrane. These are extremely simple and lack these internal bodies. Normally, the only membranes that prokaryotes possess are those in charge of delimiting the organism with the external environment (note that this membrane is also present in eukaryotes).
Nucleus: As mentioned previously, the presence of a nucleus is a key element to discriminate between both groups. In prokaryotes, the genetic material is not delimited by any type of biological membrane.
In contrast, eukaryotes are cells with a complex internal structure and, depending on the cell type, have the specific organelles that were described in detail in the previous section. These cells usually have a single nucleus with two copies of each gene – as in most human cells.
In eukaryotes, DNA (deoxyribonucleic acids) is highly organized at different levels. This long molecule is associated with proteins, called histones, and compacts at such a level that it can enter a small nucleus, which can be observed at a certain point in cell division as chromosomes.
Prokaryotes do not have these sophisticated levels of an organization. Generally, the genetic material is presented as a single circular molecule that can adhere to the biomembrane that surrounds the cell. However, the DNA molecule is not randomly distributed. Although it is not wrapped in a membrane, the genetic material is located in a region called the nucleoid.
Mitochondria and chloroplasts :
In the specific case of mitochondria, these are cellular organelles where the proteins necessary for cellular respiration processes are found. Prokaryotes – which must contain these enzymes for oxidative reactions – are anchored in the plasma membrane. Likewise, if the prokaryotic organism is photosynthetic, the process is carried out in the chromatophores.
Ribosomes: Ribosomes are the structures in charge of translating messenger RNA into the proteins that this molecule encodes. They are quite abundant, for example, a common bacterium, like Escherichia coli, can have up to 15,000 ribosomes.
Two units that make up the ribosome can be distinguished: one larger and one smaller. The prokaryotic lineage is characterized by presenting 70S ribosomes, consisting of the large 50S subunit and the small 30S subunit. On the contrary, eukaryotes are composed of a large 60S and a small 40S subunit.
In prokaryotes, ribosomes are scattered in the cytoplasm. While in eukaryotes they are anchored to membranes, as in the rough endoplasmic reticulum.
Cytoplasm: The cytoplasm in prokaryotic organisms has a largely granular appearance, thanks to the presence of ribosomes. In prokaryotes, DNA synthesis occurs in the cytoplasm.
Cell wall presence: Both prokaryotic and eukaryotic organisms are delimited from their external environment by a double biological membrane of a lipid nature. However, the cell wall is a structure that surrounds the cell and is only present in the prokaryotic lineage, in plants, and in fungi.
This wall is rigid and the most intuitive general function is to protect the cell against environmental stress and against possible osmotic changes. However, at the composition level, this wall is totally different in these three groups.
The bacterial wall is made up of a compound called peptidoglycan, made up of two building blocks linked by β-1,4-type linkages: N-acetyl-glucosamine and N-acetylmuramic acid.
In plants and fungi – both eukaryotes – the wall composition also varies. In the first group is cellulose, a polymer made up of repeating units of glucose sugar, while fungi have chitin walls and other elements such as glycoproteins and glucans. Note that not all fungi have a cell wall.
DNA: The genetic material between eukaryotes and prokaryotes varies not only in the way it is compacted but also in its structure and quantity. Prokaryotes are characterized by low amounts of DNA, ranging from 600,000 base pairs to 8 million. That is, they can code from 500 to a few thousand proteins.
Introns (DNA sequences that do not code for proteins and are found to be disrupting genes) are present in eukaryotes rather than prokaryotes. Horizontal gene transfer is a significant process in prokaryotes, whereas in eukaryotes it is practically absent.
Cell division processes: In both groups, the cell volume increases until it reaches an adequate size. Eukaryotes undergo division by a complex process of mitosis, which results in two daughter cells of similar size. The function of mitosis is to ensure an appropriate number of chromosomes after each cell division.
An exception to this process is the cell division of yeasts, particularly of the Saccharomyces genus, where the division leads to the generation of a smaller daughter cell since it is formed using a “bulge”.
Prokaryotic cells do not carry undergo cell division by mitosis – an intrinsic consequence of lack of nucleus. In these organisms, division occurs by binary division. Thus, the cell grows and divides into two equal parts. Certain elements participate in cell division in eukaryotes, such as centromeres. In the case of prokaryotes, there are no analogs to these and only a few species of bacteria have microtubules. Reproduction of the sexual type is common in eukaryotes and uncommon in prokaryotes.
Cytoskeleton: Eukaryotes have a very complex organization at the cytoskeleton level. This system is made up of three types of filaments classified by their diameter in microfilaments, intermediate filaments, and microtubules. In addition, there are proteins with motor properties associated with this system.
Eukaryotes have a series of extensions that allow the cell to move around in its environment. These are the flagella, whose shape is reminiscent of a whip and the movement is different in eukaryotes and prokaryotes. The cilia are shorter and generally occur in high numbers.
Frequently Asked Questions on Eukaryotic Cell
What is a eukaryotic cell?
Answer: Definition of eukaryotic cells. Eukaryotic cells are cells that contain a nucleus and organelles and are enclosed by a plasma membrane. Organisms that have eukaryotic cells include protozoa, fungi, plants, and animals.
What are 4 examples of eukaryotic cells?
Answer: All protists, fungi, plants, and animals are examples of eukaryotes.
- Protists are single-celled eukaryotes.
- Fungi can have one or more cells.
- The plants. All of the approximately 250,000 plant species, from simple mosses to complex flowering plants, belong to eukaryotes.
- The animals.
Where are eukaryotic cells found?
Answer: Eukaryotic cells are found in higher organisms like animals, plants, fungi like molds, and yeasts. They are characterized by having a true nucleus surrounded by a nuclear membrane, they also have mitochondria responsible for producing the energy necessary for cell growth and repair.
What are the two main types of eukaryotic cells?
Answer: There are four types of eukaryotes: animals, plants, fungi, and protists. Protists are a group of organisms defined as eukaryotes but not animals, plants, or fungi; This group includes protozoa, slime molds, and some algae. Protists and fungi are usually single-celled, while animals and plants are multicellular.
What is special about eukaryotic cells?
Answer: Eukaryotic cells contain 80S ribosomes in the rough endoplasmic reticulum (membrane-bound ribosomes) and cytoplasm (free ribosomes). They contain ribosomes from the 70s in mitochondria and chloroplasts. Eukaryotic cells have developed an endomembrane system, which contains membrane-bound organelles involved in transport.
What are the three main parts of a eukaryotic cell?
Answer: Eukaryotic cells can be divided into three main parts: the cell membrane that physically separates the intracellular space from the outer space, enclosing the cell; the cytoplasm, the inner portion filled with cytosol (the aqueous fluid inside the cell); and the nucleus, the inner region enclosed in the membrane that.
What is the shape of the eukaryotic cell?
Answer: Therefore, eukaryotic cells have various shapes, such as spherical, elongated, spindle-shaped, discoidal, polyhedral, branched, oval, etc.
Are viruses eukaryotes?
Answer: Microorganisms and all other living organisms are classified as prokaryotes or eukaryotes. Viruses are considered neither prokaryotic nor eukaryotic because they lack the characteristics of living things, except the ability to replicate (which they only achieve in living cells).
What is the true difference between prokaryotes and eukaryotes?
Answer: Eukaryotic cells contain membrane-bound organelles, such as the nucleus, whereas prokaryotic cells do not. Differences in the cellular structure of prokaryotes and eukaryotes include the presence of mitochondria and chloroplasts, the cell wall, and the structure of chromosomal DNA.
Do eukaryotic cells have mitochondria?
Answer: Mitochondria are found in the cells of almost all eukaryotic organisms, including plants and animals. Cells that require a lot of energy, like muscle cells, can contain hundreds or thousands of mitochondria.
What is the ultrastructure of a cell?
Answer: The ultrastructure of a cell is its fine structure, as revealed at high magnification. Animal, fungal, and plant cells contain specialized structures for particular functions called organelles.
What are the structures of a eukaryotic cell?
Answer: In addition to the nucleus, eukaryotic cells can contain several other types of organelles, which can include mitochondria, chloroplasts, the endoplasmic reticulum, the Golgi apparatus, and lysosomes. Each of these organelles performs a specific critical function for cell survival.
What is the structure and function of a eukaryotic cell?
Answer: Like bacteria and archaea, eukaryotic cells have a plasma membrane, a phospholipid bilayer with embedded proteins that separate the cell’s internal content from its environment. The plasma membrane controls the passage of organic molecules, ions, water, and oxygen into and out of the cell.
What defines a eukaryotic cell?
Answer: Eukaryotes are organisms whose cells contain a nucleus and other membrane-bound organelles. There is a wide range of eukaryotic organisms, including all animals, plants, fungi, and protists, as well as most algae.