Lysosomes Function

A cell is made up of many different organelles. One such organelle that is found in all animal cells is lysosome. The word lysosome comes from the Greek words 'lysis', which means dissolution or destruction, and 'soma', which means body. Lysosomes were discovered by the Belgian cytologist Christian de Duve in the year 1949. These are spherical organelles that contain specialized enzymes called acid hydrolases. These organelles break up food so that it is easier to digest and uptake for the cell and the body. Lysosomes are typically found in animal cells, whereas in yeast and some plants cells, the same roles are performed by organelles known as lytic vacuoles. Lysosomes function entails digesting excess or worn-out organelles, food particles, and engulfing and destroying foreign bodies that could harm the cell, like viruses or bacteria. The membrane around a lysosome allows the digestive enzymes to work at a pH of 4.5, which is the optimum pH required by the lysosome for functioning. Lysosomes fuse with vacuoles and dispense their enzymes into the vacuoles, thereby digesting their contents.

The size of lysosomes varies between 0.1 to 1.2 μm. At a pH of 4.8, the interior of the lysosomes is acidic when compared to the slightly alkaline pH of the cytosol (pH 7.2). The lysosome maintains this pH differential by pumping positive ions, that is, protons (H+ ions) from the cytosol across the membrane via proton pumps and chloride ion channels. The lysosomal membrane protects the cytosol, and thus, the rest of the cell, from the destructive enzymes that are present within the lysosome and which are essential for lysosomes function. The cell is further additionally protected from any lysosomal acid hydrolases that leak into the cytosol as these enzymes are pH-sensitive and function less well in an alkaline environment as compared to an acidic environment. Given below are details regarding the functions of lysosomes.

What are the Functions of Lysosomes?

One needs to understand that at the cellular level, lysosomes are a cell's first line of defense. These organelles act as the disposal system of the cell. These organelles are responsible for digesting the macromolecules that pose a threat to the cell by phagocytosis. Phagocytosis process consists of ingesting dying cells, useless and unwanted foreign bodies and organelle remnants that may be present in the cytosol. However, phagocytosis is only one of the ways by which these organelles get rid of unwanted matter in the cell. The other methods that are employed for getting rid of intracellular debris includes endocytosis, wherein there are protein receptors involved which are recycled from the cell surface and autophagy, wherein old, worn out organelles reach the lysosome for destruction.

An interesting characteristic of lysosomes function is autophagy. This is because, autophagy may even lead to autophagic cell death, which is a catabolic process that involves degradation of a cell's own components through the lysosomal machinery. Thus, there is programmed cell death, or autolysis. So in such cases, the cell is digesting itself. This is the reason why lysosomes are frequently nicknamed 'suicide-bags' or 'suicide-sacs', due to their role in autolysis. Another function includes helping in repairing a damaged plasma membrane by serving as a membrane patch, and thus, sealing the wound.

Lysosomes are an important part of the cell, however, there are a number of lysosomal storage diseases that are caused due to the malfunctioning of lysosomes, or at least the malfunctioning of one of their digestive proteins. These diseases includes Tay-Sachs disease and Pompe's disease. These are caused by a defective or missing digestive proteins, which leads to the accumulation of substrates within the cell, thus, impairing metabolism.