Structure of Lysosome

 Structure of Lysosome

Lysosomes are small, spherical, membrane-bound cell organelles mainly found in animal cells. They are involved in intracellular digestion and removal of waste materials. Lysosomes contain many hydrolytic enzymes, so they are commonly called the digestive bags of the cell. They are also known as suicidal bags because, under certain conditions, their enzymes may digest the cell’s own components.Lysosomes were discovered by Christian de Duve in 1955. They are present in large numbers in cells that show active digestion, such as white blood cells, liver cells, and kidney cells. Lysosomes are generally absent or less prominent in mature plant cells because vacuoles perform similar functions in plants.

Lysosomes are usually spherical or oval in shape. Their size varies from about 0.1 to 1.2 micrometers, depending on the type of cell and its physiological activity. They are formed by the Golgi apparatus. The digestive enzymes of lysosomes are first synthesized on the rough endoplasmic reticulum, then transported to the Golgi body, where they are modified, packed, and released as lysosomes. Each lysosome is surrounded by a single unit membrane. This membrane is made up of lipoproteins and separates the digestive enzymes from the cytoplasm. The lysosomal membrane is very important because it prevents the enzymes from leaking into the cytoplasm and damaging the cell. If this membrane ruptures, the enzymes may digest cellular components.

The lysosomal membrane contains special transport proteins. These proteins help transport the digested products, such as amino acids, sugars, nucleotides, and fatty acids, from the lysosome into the cytoplasm. The membrane also contains protective glycoproteins on its inner surface. These glycoproteins protect the lysosomal membrane from being digested by its own enzymes. The interior of the lysosome contains a dense fluid called the lysosomal matrix. This matrix contains many digestive enzymes known as acid hydrolases. These enzymes work best in acidic conditions. The internal pH of lysosomes is usually about 4.5 to 5.0. This acidic environment is maintained by proton pumps present in the lysosomal membrane. These pumps actively transport hydrogen ions into the lysosome.

Lysosomes contain different types of hydrolytic enzymes. These include proteases, which digest proteins; lipases, which digest lipids; nucleases, which digest DNA and RNA; glycosidases, which digest carbohydrates; phosphatases, which remove phosphate groups; and sulfatases, which digest sulfate-containing compounds. These enzymes allow lysosomes to break down almost all types of biological molecules. Structurally, lysosomes may be of different types. Primary lysosomes are newly formed lysosomes released from the Golgi apparatus. They contain digestive enzymes but have not yet taken part in digestion. Secondary lysosomes are formed when primary lysosomes fuse with food vacuoles or damaged cell organelles. In secondary lysosomes, digestion actually takes place. Residual bodies are lysosomes that contain undigested waste materials. These wastes may remain in the cell or may be removed by exocytosis.

Lysosomes are also involved in autophagy, which means self-eating. During autophagy, damaged or old cell organelles are enclosed in a membrane to form an autophagic vacuole. This vacuole fuses with a lysosome, and the damaged organelle is digested. In this way, lysosomes help in recycling cellular materials. Another important structural feature of lysosomes is their ability to fuse with other vesicles. They can fuse with endocytic vesicles, phagosomes, and autophagosomes. This fusion ability allows lysosomes to digest materials entering the cell from outside as well as damaged parts of the cell itself.The lysosome is therefore a highly specialized organelle. Its single membrane, acidic internal environment, digestive enzymes, proton pumps, and transport proteins all work together to perform intracellular digestion. The membrane protects the cytoplasm, the acidic pH activates enzymes, and the enzymes digest complex substances into simpler molecules.