Eukaryotic cells are characterized by a complex structure. Its main components are the plasma membrane, the cytoplasm, which contains membrane organelles, inclusions, organelles without membranes and the nucleus.
Membranous organelles have one or two membranes. They are permanent elements of the cell, characterized by a peculiar structure and perform the corresponding functions.
The cell nucleus, mitochondria, and plastids (chloro-, chromo- and leucoplasts) belong to the double-membrane structures of the cell. Non-membrane elements are ribosomes and the cell center.
During the cell cycle, elements of the cytoskeleton may change. So, for example, during the process of division in the cell, cytoplasmic tubules disappear, a new structure appears - the division spindle.
Single-membrane organelles: let's dwell on their characteristics.
These structures are the constituent elements of eukaryotic cells, which are separated from the cytosol by a single membrane. Single-membrane cell organelles include the endoplasmic reticulum, the Golgi apparatus, and derivativesstructures from it - lysosomes.
The endoplasmic reticulum is a closed system of tubules that permeate the entire cytosol. It divides the cell into separate parts and is responsible for the transport of substances. The endoplasmic reticulum was discovered in 1945 using an electron microscope, which made it possible to see a particularly loose structure throughout the cytoplasm.
The endoplasmic reticulum is granular and agranular. The smooth (agranular) endoplasmic reticulum is responsible for the synthesis of lipids and polysaccharides, while the granular one contains ribosomes on its surface, in which proteins are formed. This structure facilitates the transport of various compounds throughout the cell, circulating nutrients.
It is worth noting that the granular reticulum cisterns bind to the nuclear membrane and take part in the formation of new nuclear membranes that are formed after cell division.
The Golgi apparatus can be of various shapes, but in most cases it looks like thickened discs that form a dictyosome. Tubes extend from dictyosomes, at the end of which vesicles are concentrated. The Golgi apparatus accumulates substances that are synthesized in the cell and removed from it. This organelle is well developed in glandular cells.
Its vesicles take part in the formation of the cytoplasmic membrane, as well as individual organelles - primary lysosomes.
Lysosomes are round-shaped membrane structures containing enzymes, withby means of which the cell is able to break down various organic substances. These single-membrane organelles perform another function - they break down some structural elements of cells without compromising its functioning, providing an additional source of nutrition in case of insufficient intake of nutrients. In addition, lysosomes are responsible for the destruction of dead and unnecessary organelles.
It should be noted that all single-membrane organelles are important for maintaining cellular homeostasis, as they ensure the normal functioning of cells.
