What is a lysosome?
- The word Lysosome is made up of two Greek words Lyso and Soma. Lyso means digestive and soma means action ie Lysosome means a digestive function.
- Lysosomes were discovered by De Duve. Alex Novikoff looked at the lysosome in the cell by electron microscope and named it lysosome.
- It is a single membrane binding cell that contains abundant acidic hydrolase enzymes that digest all types of organic polymers, ie carbohydrates, proteins, lipids, and nucleic acids.
- Acidic hydrolase enzyme requires an acidic environment (pH ~ 5) for its function. Which is provided by H + ATPase. Lysosome consists of V-type ATPase pumps.
- It is found in all cells except prokaryotic cells and mature RBCs. Astringent is found in abundance in cells.
- It is found less in higher grade plants.
Formation of Lysosome
- Endoplasmic Reticulum and the Golgi body through the creation of lysosomes is by.
- Enzymes of Lyso soma are produced by the endoplasmic reticulum. And the surrounding membrane is formed by Golgi work.
- For the formation of the lysosomes, the formation of the lysosomal enzymes is necessary for advancement. This formation takes place in the rough part of the endoplasmic reticulum. There they are also bound in vesicles and transported to the Golgi apparatus.
- On the cis side of the Golgi apparatus, there is a preparation for the further transport of the lysosomal enzymes. A phosphoryl group ( ) is attached to the enzyme (= phosphorylation ). Then these phosphorylated enzymes are given a marker called mannose-6-phosphate (M6P) on the trans side of the Golgi apparatus. This marker serves as a recognition molecule for lysosomal enzymes.
- In the next step, the lysosomal enzymes are packaged in vesicles. This is how the so-called primary lysosomes are formed. The M6P marker comes off and can be reused.
- All proteins that were not phosphorylated in the Golgi apparatus do not receive the M6P marker either. In this way, the cell recognizes that these are not lysosomal proteins. These proteins are then packaged in transport vesicles and exocytosed out of the cell.
- After the primary lysosomes have formed, they migrate into the cytoplasm. There they can fuse with various other vesicles and thus form secondary lysosomes.
- If a lysosome fuses with an endosome, a so-called endolysosome is created. Endosomes are formed during the endocytosis of substances outside the cell.
- With endocytosis, you can imagine a process in which substances from the outside combine with the cell membrane. This results in protuberances which then constrict. In this way, vesicles are created that contain the substance from the extracellular space.
- When a lysosome in macrophages fuses with a so-called phagosome, the phagolysosomes are formed. With a phagosome you can easily imagine an organelle that consists of a foreign body (e.g. bacteria ) in phagocytes (macrophages, granulocytes, …) that are surrounded by a membrane (= phagocytosis ). In combination with a lysosome, the phagosome receives the necessary enzymes to break down the foreign body.
Types of Lysosome
There are generally four types of lysosomes: –
- Primary lysosome
- Secondary Lysosome
- Residual body
When lysosomes are formed, acidic hydrolase is deposited in an inactive form. This acidic hydrolase acts only in an acidic medium. It is also called Storage Granules.
It is formed by the fusion of primary lysosomes and phagosomes or vacuoles. They are also called Digestive Vacuoles and Heterophagosome.
The lysosome contains indigestible material or waste material, which is exited from the cell by exocytosis.
Lipofuscin granule – Residual function is extracted from the cell by exocytosis or placed within the organism as a lipofuscin particle.
Lysosome by which the cells of its cell are exposed. Called autophagosomes or autolysosomes.
Disease-related to Lysosome
- Gaucher’s disease
- Pompe’s disease
- Tay-Sachs disease
What is the function of a lysosome?
- Digestion of particles entering the cell through phagocytosis or pinocytosis. This is called heterophagy.
- Digestion of internal substances of the cell. This is called autophagy.
- The autolysis process destroys old cells and infected cells. All the lyso-soma of the cell bursts, causing all its digestive enzymes to digest the cells. Therefore, it is also called a Suicidal bag of the cell.
The most important function of a lysosome is to break down cellular and non-cellular substances. To do this, it includes the substance to be digested (protein, …) in its interior.
Digestion of foreign matter
A lysosome can break down substances and toxins that are foreign to cells (= heterophagy). This could be parts of alcohol or nicotine, for example.
To do this, the primary lysosomes combine with the endosomes that contain these non-cellular substances. The resulting endolysosomes can break down the non-cellular substances using hydrolytic enzymes. Some endolysosomes can even send small parts of the substance to the cell membrane. These act as antigens to support your immune system and arm your cells for renewed contact with this substance.
Digestion of the cell’s substances
A lysosome is also able to digest the cell’s substances such as parts of organelles or the cytosol (= autophagy). These can then even be recycled if necessary. So the lysosome is a kind of repair vesicle for your cells.
With their enzymes, the lysosomes contribute to what is known as apoptosis. This is regarded as the programmed death of a cell and leads to cells unnecessary for the organism being specifically broken down.
For example, the tail of a tadpole or the webbed fingers of a human embryo is broken down by apoptosis.
- A lysosome has a rounded shape and is surrounded by a membrane. It is roughly up to 1 in size.
- The pH value in its interior (= lumen) is acidic and is roughly in the range of 4.5 – 5. The cytosol in which the lysosomes move has a neutral pH value of approx. 7.2.
- In this acidic environment, the various enzymes such as lipases, proteases, and nucleases are highly active. These so-called hydrolytic enzymes can split lipids, proteins, nucleic acids, and polysaccharides through hydrolysis. Without the acidic environment, these enzymes would not be able to work effectively, they would not break down the substances mentioned, and the lysosome would not be able to digest the substances.
- To ensure the low pH value, the lysosome needs the transport protein V-type ATPase, which is embedded in the lysosome membrane. V-type ATPase can hydrolyze ATP and thereby “pump” photons from the cytosol through the membrane. Since the pH value decreases with an increasing number of ions, a consistently acidic environment is created in the lysosome.
What is a Lysosome? Function, Formation, Types, & Structure1