Endoplasmic reticulum: structure and function

The endoplasmic reticulum is the obligatory organelle of the eukaryotic cell. It is found in plant, animal and human cells. The functions of this constituent part of the cell are diverse and related mainly to the synthesis, modification and transport of organic compounds.

For the first time the endoplasmic reticulum was discovered in 1945. American scientist K. Porter saw it with the help of one of the first electric microscopes. From this time, her active research began.

In the cell there are two varieties of this organelle:

• Granular, or rough endoplasmic reticulum (covered by a multitude of ribosomes).
• Agranular, or smooth endoplasmic reticulum.

Each type of reticulum has some features and performs completely different functions. Let's look at them in more detail.

Granular endoplasmic reticulum: structure . This organelle is a system of cisterns, vesicles and tubules. Its walls consist of a bilipid membrane. The width of the cavity can vary from 20 nm to several micrometers - here everything depends on the secretory activity of the cell.

In few specialized cells that are characterized by a low level of metabolism, EPS is represented by only a few scattered cisterns. Inside the cell, which actively synthesizes protein, the endoplasmic reticulum consists of a multitude of cisterns and a branched tubule system.

As a rule, granular EPS by means of tubules is connected with the membranes of the nuclear envelope - this is how complex processes of synthesis and transport of protein molecules occur.

Granular endoplasmic reticulum: functions . As already mentioned, the entire surface of EPS from the side of the cytoplasm is covered with ribosomes, which, as is known, are involved in protein synthesis. EPS is a place for the synthesis and transport of protein compounds.

This organelle is responsible for the synthesis of integral proteins of the cytoplasmic membrane. But in most cases, the created protein molecules are then transported via the membrane vesicles to the Golgi complex, where they are further modified and distributed according to the needs of the cell and tissues.

In addition, some changes in the protein occur in the cavities of the EPS, for example, the addition of a carbohydrate component to it. Here, by aggregation, large secretory granules are formed.

Agranular endoplasmic reticulum: structure and function . The structure of a smooth EPS has some differences. For example, such an organelle consists only of cisterns and does not have a system of tubules. Complexes of such EPS, as a rule, are smaller, but the width of the tank, on the contrary, is greater.

A smooth endoplasmic reticulum is not related to the synthesis of protein components, but performs a number of equally important functions. For example, it is here that the synthesis of steroid hormones occurs in humans and all vertebrates. That is why the volume of smooth EPS in adrenal cells is quite large.

In liver cells EPS makes the necessary enzymes, which are involved in carbohydrate metabolism, namely in the breakdown of glycogen. It is also known that liver cells are responsible for the detoxification of toxins. In the tanks of this organelle, a hydrophilic component is synthesized, which then joins the toxic molecule, increasing its solubility in blood and urine. Interestingly, in hepatocytes, which are constantly susceptible to toxins (poisons, alcohol), almost the entire cell is occupied by densely located tanks of smooth EPS.

In muscle cells there is a special type of smooth EPS - sarcoplasmic reticulum. It acts as a depot of calcium, thus regulating the processes of activity and rest of the cell.

As can be seen, the functions of EPS are diverse and very important for the normal functioning of a healthy cell.