Each living cell has a set of structures that enable it to demonstrate all the properties of a living organism. In order to function properly, the cell must receive enough nutrients, break them down and release energy, which is then used to support life processes.
At the first stage of complex processes of energy management are the lysosomes of the cell, which are laced along the edges of the flattened cisterns of the dictyosome (Golgi complex).
How lysosomes work
Lysosomes are spherical single-membrane bodies with a diameter of 0.2 to 2 microns, which contain a complex of hydrolytic enzymes. They are able to break down any natural polymer or substance of a complex structure that enters the cell as a nutrient substrate or a foreign agent:
- proteins and polypeptides;
- polysaccharides (starch, dextrins, glycogen);
- nucleic acids;
- lipids.
This efficiency is provided by about 40 different types of enzymes contained inboth in the matrix of the lysosome and on the inner side of the membrane in an adhered state.
Lysosome Chemistry
The membrane surrounding the lysosome protects the organelles and other components of the cell from being digested by the enzyme complex. But after all, in the vesicle itself, all enzymes are of protein origin, why are they not broken down by proteases?
The fact is that inside the lysosomes the enzymes are in a glycosylated state. This carbohydrate "shell" makes them poorly recognized by proteolytic enzymes.
The reaction of the environment inside the lysosome is slightly acidic (pH 4.5–5), in contrast to the almost neutral reaction of the hyaloplasm. It creates favorable conditions for the action of enzymes and is provided by the work of H+-ATPase, which pumps protons into the organelle.
Lysosome conversion process
Morphologically, two main types of lysosomes are distinguished in the cell - primary and secondary.
Primary lysosomes are small vesicles, smooth-walled or bordered, separated from the cisternae of the Golgi complex. They contain a set of hydrolytic enzymes previously formed on the membranes of granular (rough) EPR. Until the absorption of the nutrient substrate, lysosomes are in an inactive form.
For enzymes to work, food particles or liquids must enter the lysosome. This happens in two ways:
- By autophagy, when a food particle is taken up by a lysosome from the surrounding cytoplasm. In this case, the membrane of the organelle invaginates at the point of contact with the particleand forms an endocytic vesicle, and then laces into the lysosome.
- By heterophagy, when the lysosome fuses with endocytic vesicles trapped in the cytoplasm of the cell as a result of absorption of solid particles or liquids from outside.
Secondary lysosomes are vesicles containing both enzymes and substrate for digestion. They are characterized by pronounced hydrolytic activity and are formed as a result of absorption of the substrate by the primary lysosome.
Despite the fact that the functions of the lysosome are reduced to the digestion (breakdown) of solid organic particles and dissolved substances, the versatility of the process is ensured by the ability of secondary lysosomes:
- merge with primary lysosomes that bring in a new portion of enzymes;
- fuse with new food particles or endocytic vesicles, maintaining a continuous breakdown process;
- fuse with other secondary lysosomes to form a large structure capable of absorbing other cell organelles;
- absorb pinocytic vesicles, turning into a multivesicular body.
The structure of the lysosome does not change dramatically. It usually only increases in size.
Other types of lysosomes
Sometimes the breakdown of substances that have entered the lysosome does not go to the end. Undigested particles are not removed from the organelle, but accumulate in it. After the supply of hydrolytic enzymes is depleted, the contents are compacted and processed, the structure of the lysosome becomes more complex, layered. Pigments may also be deposited. The lysosome transforms into a residual body.
In the future, residual bodies remain in the cell or are removed from it by exocytosis.
Autophagosomes can be found in protist cells. By their nature, they belong to secondary lysosomes. Inside these organelles, remnants of large cell components and cytoplasmic structures are found. They are formed during cell damage, aging of cell organelles and serve to utilize cell components, releasing monomers.
Functions of the lysosome in the cell
Lysosomes, first of all, provide the cell with the necessary building material, depolymerizing substances that have entered it.
The breakdown of carbohydrates is an important link in the cell's energy metabolism, supplying a substrate for conversion in mitochondria.
Lysosomes are also a defense link in the body's immune system:
- After phagocytosis of bacteria by leukocytes, lysosomes pour their contents into the cavity of the phagocytic vesicle and destroy the harmful microorganism.
- Release proteolytic enzymes during apoptosis - programmed cell death.
- Utilize damaged and "aged" cell organelles.
In combination with cell proliferation, the participation of lysosomes in the process of utilization of various structures ensures the renewal of the body.
