How is a cell able to “digest” substances that enter the cytoplasm? The answer can be obtained by considering what lysosomes are. What is their structure? Due to what properties are these organelles capable of performing their function?
Lysosomes. Features of the structure and function
A lysosome is an organoid of a cell about 0.2 microns in size, surrounded by a single membrane and containing hydrolytic enzymes. The main function of such vesicles is the breakdown of substances that enter the cell through endocytosis, or their own molecules, which are no longer needed.
What are lysosomes in terms of structure?
The splitting, or degradation of substances, is carried out using hydrolases - enzymes that can work in an acidic environment. To maintain a low pH, vacuolar- type ATPases (V-type) are embedded in the lysosome membrane . The specific structure of this complex allows hydrogen protons to be pumped against the concentration gradient , thereby increasing their amount in the internal environment of the organelle.
Hydrolases are able to function only in an acidic environment. This plays an important protective role, since the environment is almost neutral in the cytoplasm of the cell . If the lysosome membrane is somehow damaged and the enzymes enter the cytosol, they will lose the ability to break down substances and organelles.
The lysosome membrane consists of lamellar and micellar sites. The gaps between the layers of phospholipids are filled with water. Numerous pores are scattered throughout the membrane, which are also filled with water and can be closed by polar molecules. Such a complex of sections of the membrane and the pore system makes it possible to penetrate into the organelle of both hydrophobic and hydrophilic molecules.
How are lysosomes formed?
The proteins needed to build the lysosome are initially synthesized in the EPR. Next, they must be "marked" by attaching the mannose residue. This mannose residue is a specific signal for the Golgi apparatus: proteins are concentrated in one place, after which a bubble with lytic enzymes is synthesized from them. This is what lysosomes are in biology.
The internal contents of lysosomes
What are lysosomes and what is the composition of the internal environment of these organelles?
Inside the lysosome, an acidic medium is maintained, the pH of which reaches 4.5-5. Under such conditions, enzymes can fulfill their cleavage function. Hydrolases are the common name for a whole class of enzymes. In total, the lysosome contains about 40 different biologically active molecules that catalyze their completely specific reaction.
The following enzymes can be found in the composition of the internal contents of the lysosome:
- acid phosphatase - breaks down substances containing phosphate groups;
- nuclease - destroys nucleic acids;
- protease - breaks down proteins;
- collagenase - destroys collagen molecules;
- lipase - breaks down esters ;
- glycosidases - accelerate the breakdown of carbohydrates;
- asparaginase - breaks down aspartic acid;
- glutaminase - destroys glutamic acid.
In total, about 40 different types of hydrolases are contained in lysosomes. Therefore, the question of what lysosomes can be answered in biology: a storehouse of enzymes.
Types of Lysosomes
There are 4 types of lysosomes: primary and secondary lysosomes, autophagosomes and residual bodies.
The formation of lysosomes is a complex process, which is accompanied by the work of various signaling molecules on the surface of EPR and AG. The primary lysosome is a small vesicle that is cleaved from the membrane by the Golgi apparatus.
The primary lysosome initially contains the entire complex of enzymes necessary for the breakdown of macromolecules.
Secondary lysosome is a large structure. It is formed by the fusion of the primary vesicle with substances trapped by endocytosis, or with metabolic products of the cell that must be disposed of.
The formation of autophagosomes is associated with a process such as autophagy - the absorption and "digestion" of spent cell organelles.
The average duration of mitochondria is 10 days. Once the organelle is unable to perform its functions, it must be disposed of. For this, many primary lysosomes surround the mitochondria and connect with each other. As a result, a large autophagosome is formed, inside which the cleavage of mitochondria into monomers begins.
What are residual body lysosomes? This is the final point of functioning of any lysosome, when the enzymes have completed their work, and there are substances left in the organelle that cannot undergo further cleavage. Undigested residues are simply thrown out of the cage.
Lysosome Disorders
Enzymes do not always work properly. Lysosomes perform the cleavage function only when the hydrolases have no structural disturbances. Therefore, many diseases associated with lysosomes are based on the improper functioning of enzymes.
Such deviations are called accumulation diseases. This means that if some enzyme is deficient, its main substrate simply does not digest in the lysosome, which accumulates and causes adverse effects.
Sphingolipidosis, Tay-Sachs syndrome, Sandhoff disease, Nyman-Peak disease, leukodystrophy - all these diseases are associated with the malfunctioning of lysosome enzymes or their complete absence. Most diseases are recessive.