Lysosome: Definition, characteristics and function 29th September 2022 – Tags: lysosomes
In this article we give you the definition of a lysosome, its characteristics and function, as well as its structure and types.
Cells are units that function as small, precise machines that keep all the activities organisms need going. This work is carried out by organelles, which are small subunits within the cell. It is essential that one of them is responsible for assimilating everything that is produced inside the cell, these are the lysosomes.
What are lysosomes – Definition
Lysosomes are organelles located inside the cell. They have a function similar to that of the stomach, performing cellular digestion. They contain encapsulated hydrolase enzymes that help break the bonds of proteins, nucleic acids and sugars to create simpler, lower molecular weight particles that can be reintroduced into metabolic pathways.
Characteristics of lysosomes
Now that you know that lysosomes are cell organelles, let’s look at their most important characteristics:
- The lysosome is of animal origin: lysosomes are present in the cell, but only in animal cells.
- They are spherical in shape and originate from the Golgi apparatus.
- They are polymorphic: that is, they do not have a specific size. In fact, they can have different contents.
- There is more than one lysosome per cell: there cannot be only one lysosome, there must be several.
- They are delimited from the outside by a simple membrane: it is impermeable to external substances.
- They need intermediate proteins: they are integrated into the membrane and use them to communicate with the outside world.
- They contain a large number of enzymes.
- Their internal matrices have a very acidic pH of 5: this is so that the enzymes they contain can be functional.
- They have a highly glycosylated inner haemimembrane: this serves to protect them from very acidic pH, which means that proteins bind to oligosaccharides.
Types of lysosomes
The first classification of these organelles can be grouped into two categories:
Primary lysosomes: are the first to form and are very young. They have not started their digestion process and are small and homogeneous, between 0.05 and 0.5 microns in diameter. They are found near the trans side of the Golgi apparatus, which is the area that sends out the vesicles.
Secondary lysosomes: These are the lysosomes that are already active and digesting. They are different sizes from each other. They are larger than primary lysosomes because they are already processing molecules.
Depending on what they engulf, lysosomes can also be classified into several categories:
Heterolysosome: are molecules that digest molecules, bacteria and viruses. Discover the difference between viruses and bacteria.
Autolysosome: are those that completely digest the cell by apoptosis.
Function of lysosomes
The function of these organelles is to digest substances (cellular digestion) that are inside the cell and also those that enter the cell from the outside. This digestion has four purposes:
Recycling
The first function of lysosomes is to process molecules for recycling in the cell’s metabolism. By transforming them into simpler molecules, they can be reused. This is an excellent strategy to avoid waste and energy expenditure. They transform, for example, proteins into amino acids, large sugar molecules into simple sugars and lipids into simple fatty acids.
Elimination
The second purpose of digestion is to remove organelles or proteins that have deteriorated over time. Deteriorated organelles can generate reactive oxygen species, which cause ageing. Lysosomes have the capacity to completely engulf these organelles and even portions of the cytoplasm that need to be renewed.
Regulation
On the other hand, this process also regulates cell growth, as this process gives the cell balance while regulating cell homeostasis, which keeps the cell in equilibrium in the face of external changes. If the cell is completely disturbed, the lysosomes lead to apoptosis or programmed cell death, where they self-destruct the cell.
Collaboration
Finally, lysosomes help to get rid of external threats, such as bacteria or viruses, by processing them to break them down and expel them when they become inactive. Learn about all types of bacteria.
The lysosome process is completed by endocytosis, a process in which the particles in question are engulfed and enveloped in vesicles. These vesicles are called digestive vacuoles and, once they have processed the contents, they return them to the cell for reuse. What cannot be digested is released from the cell.
When lysosomes do not function properly, they can lead to multiple diseases. As they have several functions, there are many diseases that result from their malfunction. They are rare and genetic in origin, but some of them are Gaucher disease and Pompe disease.
Structure of lysosomes
They are organelles of relatively simple structure. They consist of a lipid bilayer into which are inserted carrier proteins that allow the passage of particles in and out. Numerous particle-processing enzymes are found within the lipid bilayer, for example:
- Alfa-glucosidasa
- Colagenasa
- Elastasa
- Ribonucleasa
- Lipasas