Definition, Structure & Examples I

Living things are classified into prokaryotes and eukaryotes. In both cases, it is a question of a group of living beings that differ from each other in terms of a specific cell structure. Unlike prokaryotes, all eukaryotic organisms have a cell nucleus. Eukaryotes include living beings such as humans, animals, plants and fungi.

Eukaryotes definition

eukaryotic structure

Within an organism there are many different cells that are specialized in different ways. For example, more mitochondria can be found in cells that require a lot of energy than in other cells. A specialization of cells is therefore essential for the maintenance of an organism.

In general, you can understand the cell nucleus as a distinguishing feature for eukaryotes. This is present in every eukaryotic cell. In general, eukaryotic cells are also referred to as eucytes.

However, the compartmentalization, i.e. the structure of a cell into various cell organelles, differs in the various eukaryotic organisms. The only thing that eucytes have in common is that they are much more compartmentalized than prokaryotic cells.

The compartmentalization offers the great advantage that different biochemical reactions can take place simultaneously in the cell. In some cases, different reactions also require different reaction conditions. For example, so that the citric acid cycle and the end oxidation in the respiratory chain can take place simultaneously in the mitochondria, the mitochondria are divided into two compartments by an outer and an inner membrane.

Oxidative decarboxylation and the citric acid cycle take place in the matrix of the mitochondria, while ATP production takes place in the respiratory chain via the inner membrane and the intermembrane space.

cell organelles

The following cell organelles are found in both animal and plant cells:

Cell organelleFunctionCell nucleus (nucleolus)- surrounded by a double membrane with nuclear pores- information and control center- contains the DNA in the form of chromatids- site of transcription during protein biosynthesis- control of gene regulationRibosomes- consist of two subunits- serve as the site of protein synthesis, since the mRNA during translation it is translated into a protein Endoplasmic reticulum (ER)- a labyrinthine Cavity system of tubes, cisterns and sacs – surrounded by a membrane – distinction between smooth and rough ER – the rough ER is occupied by ribosomes – is used for substance production, substance transport and substance distribution Dictyosome – all dictyosomes in a cell are referred to as the Golgi apparatus – substance delivery , onward transport by packaging in vesicles- can be understood as «post office» or «warehouse» within the cellMitochondria- can be understood as «power station» of the cell- surrounded by double membrane- site of cellular respiration; Generating energy by breaking down glucose into CO2 and H2O, yielding ATPCytoplasma- aqueous substance containing various organic cell contents such as proteins, cell organelles, cytoskeleton, actin filaments or RNA

Although all eucytes have a cell nucleus in common, they are not structured in the same way. A distinction is made between an animal, a plant and a fungal cell. The different cell structures are illustrated below using various eukaryotic protozoa.

animal cell

In addition to the cell organelles listed above, the animal cell has the following special features that cannot be found in other eucytes:

Cell organelle function Lysosomes – surrounded by a single membrane – contains various degrading enzymes, which break down harmful products and synthesize new ones – can be understood as the «recycling plant» of the cell Desmodesmata through «holes» in the cell membrane called pits, the desmodesmata create a cell-cell connection

Figure 1: Animal cell

plant cell

The following cell organelles that cannot be found in a fungal cell or animal cell can be found in the plant cell:

Cell organelle function chloroplasts – chloroplasts belong to the plastids – are surrounded by a double membrane – the inner membrane is constructed according to the principle of surface enlargement, which serves to protect the cell organelle and increase capacity; Formation of thylakoids- in thylakoids (cavities) is the photopigment chlorophyll site of photosynthesis; Chloroplasts can be compared to a solar system that converts light into energy when exposed to sunlight- photosynthesis allows autotrophic nutrition of the cellPlasmodesmata- through «holes» in the cell wall called pits, the plasmodesmata create a cell-cell connectionvacuole- filled with liquid- maintains the pressure in of the cell upright, so that the cell does not collapse – can digest harmful substances similar to the lysosomes in an animal cell cell wall – «wall» which protects the interior of the cell from the «outside» – cellulose as a substance in the cell wall

Figure 2: Plant cell

fungal cell

The fungal cell has another special feature. Like plant cells, fungal cells have a cell wall. However, the cell wall is made of chitin. Also, like animal cells, fungi have vacuoles.

Nevertheless, fungi also differ from plants because they have no chlorophyll and no chloroplasts. As in animal cells, energy is generated by breaking down glucose. The individual cells are connected by a septum, which enables an exchange of substances between the cells.

Figure 3: Fungal cell

Gene regulation in eukaryotes

Controlling the activity of genes is an important cellular mechanism that affects cell development. The cell can regulate the formation of proteins via gene regulation and thus react to changes in environmental conditions.

In eukaryotes, gene regulation can take place at different levels and thus at different times:

Comparison of eukaryotes and prokaryotes

According to the endosymbiont theory, eukaryotic organisms should have evolved from prokaryotic organisms. However, there are large differences between the organisms. These relate in particular to cell size, compartmentalization, the organization of DNA, gene regulation and the movement of living beings.

EukaryotesProkaryotesZellizeEukyte has a diameter of 10 to 30 µm.A procyte has a diameter of 1-2 µm.CompartmentalizationThe compartmentalization of a eucyte is significantly greater, since more cell organelles are separated from each other by cell membranes.A procyte has no compartmentalization.DNAThe DNA is located in the nucleus of the cell and is present there in the form of chromosomes. The DNA is not separated but moves freely in the cytoplasm. It is constructed in the form of a ring.Gene regulationThere are various control mechanisms for gene regulation in eukaryotes, which can occur at different levels of protein biosynthesis.Gene regulation in prokaryotes can only take place during transcription according to the operon model.MovementEucytes can move using flagella, which begin at the cell body and are surrounded by a cell membrane. The cell can move by moving up and down. This is the case, for example, with sperm. Procytes can move through protein threads outside the cell wall. These are flagella, which set the movement of the cell in motion through rotation.