Nucleus, Golgi apparatus, mitochondria… an organelle is a compound of the eukaryotic cell endowed with a specific function and delimited by a phospholipid membrane. Explanations.

An organelle, also called organelle by Anglicism, is a structure providing a specific function in the cytoplasm of a cell. Organelles are delimited from the rest of the cell by a phospholipid membrane.

Classically, we believe that only eukaryotic cells contain organelles, unlike prokaryotic cells. Indeed, eukaryotic cells have a structured organization, endowed with a nucleus and organelles grouping together the genetic material and separated from the rest of the cell by a membrane. Conversely, prokaryotic cells lack a nucleus and the genetic material is not separated from the rest of the cell.

As a reminder, the term eukaryote designates unicellular or multicellular organisms such as animals, plants and fungi. For their part, prokaryotes correspond to the unicellular organisms constructing bacteria.

Structures with a membrane

For some authors, the term organelle refers only to structures separated from the cell by a membrane, such as the nucleus, mitochondria, Golgi apparatus, and endoplasmic reticulum.

But this definition has been questioned by some scientists who have distinguished between membrane organelles and those not bound to a membrane. These are called large biomolecular complexes, among them are:

• llarge complexes of RNA and proteins (ribosome, spliceosome, vault);
• llarge protein complexes (proteasome, holoenzyme de l ‘DNA polymerase III, holoenzyme of the ‘RNA polymerase II, capsides symmetrical viral, GroEL and GroES complex);
• membrane protein complexes (photosystem I, ATPsynthase);
• llarge complexes of DNA and proteins (nucleosome);
• le centriole ;
• the microtubules ;
• le cytosquelette ;
• the flagella;
• le nucleolus ;
• granules stress ;
• granules germ cells ;
• les granules de transport neuronal, etc.

Structures belonging to eukaryotic cells

Classically, organelles are considered to be structures observed only within eukaryotic cells. However, for part of the scientific cohort, the organelle covers a broader definition, grouping together all the compounds of a eukaryotic cell but also certain micro-compartments of prokaryotic cells based on proteins (and acting as primitive organelles). ).

Structures that contain DNA

Some biologists have chosen to delimit the term organelles to cellular compartments containing DNA (or deoxyribonucleic acid). According to this definition, there would be two main classes of organelles:

• mitochondria (found in almost all eukaryotes);
• the plastes (in plants).

Organelles present in the eukaryotic cell

• Le core surrounded by an envelope formed by a double membrane and which contains theADN ;
• The endoplasmic reticulum which includes: the rough endoplasmic reticulum (traversed by ribosomes ensuring the production of proteins), the smooth endoplasmic reticulum (whose membrane is smooth due to the absence of ribosome). The endoplasmic reticulum contributes to the production of internal membranes and vesicles;
• theGolgi apparatus which allows the “sorting” of molecules produced by the cell;
• the lysosomes dhave them digestive enzymes ensure the decomposition (hydrolysis) of used molecules and organelles;
• the peroxysomes which contribute to metabolism of the lipids and carbohydrates ;
• les mitochondriai allow the cellular respiration and the production ofATP from carbohydrates.

In plant cells, we also find:

• of the plastes who convert theenergy luminous in chemical energy;
• la central vacuole whose membrane is the tonoplast. The vacuole allows the storage of nutrients, and guarantees the cell growth.

The analogy between body organs (or viscera) and microscopic cell substructures is obvious. It is also mentioned in the first school textbooks in which the authors rarely distinguished between the two. But in the 1830s, French biologist Félix Dujardin refuted the idea that microorganisms have the same organs as multicellular organisms (like animals). Then in August 1884, the German zoologist Karl August Möbius, in a footnote, used the term organella to refer to the organs of unicellular compounds.