Information

Atlas of Botany: Eukaryotes

Atlas of Botany: Eukaryotes

Eukaryotic cell

The eukaryotic cell is made up of a protoplasm, formed by nucleus and cytoplasm, and one plasma membrane or mobile phone.
The eukaryotic cell is composed of numerous structures: the description of the main parts found in animal and plant cells is given below.
Not all cells have the same organelles; in multicellular organisms, depending on the specialization they assume, there may be numerous exceptions compared to the basic model. Just to cite an example, red blood cells are cellular structures that have no nucleus at maturity.
So let's see what organelles we can find in a generic cell, animal or plant.

Plasma or cell membrane
Structure: double layer of phospholipids, proteins and glucidispessore of about 7 nanometers
Functions: keeps the internal environment constant, acts as a selectively permeable membrane, modifies its shape according to the needs of the cell, allows the useful substances to enter and lets the waste ones out.

Cytoplasm
The cytoplasm is composed of a viscous and very fluid part, the cytosol, made up of water (which represents 75-85% of the total weight of the cell), of inorganic substances dissociated in ionic form (especially K +, Na +, Ca ++ and Mg ++ ions ) and from various organic molecules (including proteins with enzymatic or structural function).
The cytoplasm of eukaryotic cells includes numerous cytoplasmic structures of various types, which perform very specific functions (in prokaryotes cellular activities exist, but are not carried out by distinct structures). Some of these structures (also called organelles) are delimited by a structured membrane such as the plasma membrane, but with modifications in the type and number of phospholipids and proteins that allow them to perform particular functions.

Cytoskeleton
Inside the cell, the presence of a dense interweaving of protein fibers has been highlighted which give shape to the cell and attack on the cellular organelles.
The fibers that make up this structure are different from each other:
- microtubules - hollow structures with a diameter of about 25 nm. They branch off from the core area;
- actin filaments - diameter up to 7 nm, consisting of two filaments twisted together. They are arranged in parallel bundles;
- intermediate filaments - formed by three twisted filaments, made up of resistant fibrous proteins. They form bundles that guarantee structural reinforcement to the cell.

Endoplasmic reticulum
Smooth Endoplasmic Reticle (REL)
It consists of a system of flattened vesicles that allow the movement of substances from one part of the cell to another; it is the site of the synthesis of phospholipids and glycoproteins necessary for the construction of the membrane; plays an important role in glucose metabolism and controls the movement of Ca2 + ions during muscle contraction (in animal cells).

Rough Endoplasmic Reticulum (RER)
It is coated with spheroidal particles, the ribosomes. It is in direct connection with the smooth endoplasmic reticulum and with the nuclear membrane. Transport vesicles detach from the smooth endoplasmic reticulum and will reach the Golgi apparatus, within which the construction of the protein molecule will end.

Ribosomes
These organelles are made up of RNA and proteins and have the function of synthesizing new proteins. Their number in the cell ranges from a few thousand in prokaryotes to a few million in eukaryotes. We can find ribosomes both linked to the membranes of the lattice and free in the cytoplasm.
The ribosomes of prokaryotes have some differences in structure and composition compared to those of eukaryotic cells; this fact makes possible treatments with antibiotics that attack only the bacterial ribosomes by interrupting the metabolism of these pathogens, without damaging the patient's ribosomes.

Nucleus
The nucleus is the organelle which contains all the genetic information for the control of cellular metabolism. It has a diameter of about 5 microns and is delimited by a double membrane on the surface of which there are pores (diameter about 100 nanometers) which will allow the exit of the RNA and the passage of numerous other substances.
The nucleus membrane is in direct continuation with that of the endoplasmic reticulum.
DNA occurs in different forms during cell life. During the phases of cellular reproduction it is subdivided into chromosomes, structures generated by the wrapping of the double helix around proteins, while during the remaining period of the life cycle of a cell it appears as an indistinct mass called chromatin.
Inside the nucleus there is the nucleolus which is responsible for the synthesis of ribosomes.

Golgi apparatus
Consisting of overlapping lamellae and tanks, in which substances produced in other areas of the cytoplasm accumulate and are further processed. Complex molecules are built inside, such as glycoproteins.
They are more abundant in secretory cells. In animal cells there may be some tens of structures of this kind, while in plant cells they reach up to hundreds, as they participate in the construction of the cell wall during the cell division process.
It owes its name to Camillo Golgi, who described its structure in 1898.

lysosomes
They are organelles rich in digestive enzymes, which are isolated here so as not to damage the rest of the cell. They pour their contents into the food vacuoles formed with lendocytosis, where they digest the phagocytized material.
They are formed following the detachment of vesicles from the Golgi apparatus.
They are elongated organelles (0.5 to 2 micrometers) and are the energy centers of the cells.
They consist of two membranes, the innermost folded to form mitochondrial crests, which increase the active surface of the corpuscle.
In these organelles, glucose is demolished and the production of molecules rich in energy usable by the cell is produced. Their numbers vary from cell to cell; e.g. in the liver they can be between 1000 and 1600, while in the oocyte they are also 30,000.
These organelles contain, inside them, a circular-shaped DNA strand and small ribosomes that are used for the synthesis of specific proteins of sugar metabolism.

Mitochondria
They are elongated organelles (0.5 to 2 micrometers) and are the energy centers of the cells.
They consist of two membranes, the innermost folded to form mitochondrial crests, which increase the active surface of the corpuscle.
In these organelles glucose is demolished and the production of molecules rich in energy that can be used by the cell. in the liver they can be between 1000 and 1600, while in the oocyte they are also 30,000.
These organelles contain, inside them, a circular-shaped DNA strand and small ribosomes that are used for the synthesis of specific proteins of sugar metabolism.

peroxisome
They are organelles within which catalase lenzyme is present, capable of breaking down oxygen peroxide (hydrogen peroxide) into water and oxygen. It is an important corpuscle for the demolition of hydrogen peroxide, toxic to the cell, which is formed during the metabolism.


Eukaryotic cell


Video: Organelles in eukaryotic cells. Cells. High school biology. Khan Academy (September 2021).