The endoplasmic reticulum is a mandatory organelle of a eukaryotic cell. It is found in the cells of plants, animals and humans. The functions of this component part of the cell are diverse and are associated mainly with the synthesis, modification and transport of organic compounds.
The endoplasmic reticulum was first discovered in 1945. The American scientist K. Porter saw it through one of the first electric microscopes. Since that time, her active research began.
There are two varieties of this organelle in the cell:
- Granular, or rough endoplasmic reticulum (covered with many 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 tanks, vesicles and tubules. Its walls consist of a bilipid membrane. The width of the cavity can range from 20 nm to several micrometers - here everything depends on the secretory activity of the cell.
In few specialized cells, which are characterized by a low level of metabolism, EPS is represented by only a few disparate tanks. Inside the cell, which actively synthesizes protein, the endoplasmic reticulum consists of many cisterns and a branched system of tubules.
As a rule, granular EPS through the tubules is connected with the membranes of the nuclear membrane - this is how complex processes of synthesis and transport of protein molecules occur.
Granular endoplasmic reticulum: functions . As already mentioned, the entire surface of the EPS from the side of the cytoplasm is covered with ribosomes, which are known to be involved in protein synthesis. EPS is a place of 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 using 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 EPS tanks, for example, the addition of a carbohydrate component to it. Here, by aggregation, large secretory granules are formed.
Agranular endoplasmic reticulum: structure and functions . The structure of a smooth EPS has some differences. For example, such an organelle consists only of tanks and does not have a tubule system. Complexes of such EPS, as a rule, are smaller, but the width of the tank, on the contrary, is larger.
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 in humans and all vertebrates takes place. That is why the volume of smooth EPS in the cells of the adrenal glands is quite large.
EPS in the liver cells produces the necessary enzymes that 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 attaches to a toxic molecule, increasing its solubility in blood and urine. It is interesting that in hepatocytes, which are constantly influenced by toxins (poisons, alcohol), almost the entire cell is occupied by densely located tanks of smooth EPS.
In muscle cells, there is a special kind of smooth EPS - sarcoplasmic reticulum. It acts as a calcium depot, thus regulating the processes of cell activity and dormancy.
As you can see, the functions of EPS are diverse and very important for the normal functioning of a healthy cell.