What Are Lysosomes and How Are They Formed?

There are two primary types of cells: prokaryotic and eukaryotic cells. Lysosomes are organelles that are found in most animal cells and act as the digesters of a eukaryotic cell.

What Are Lysosomes?

Lysosomes are spherical membranous sacs of enzymes. These enzymes are acidic hydrolase enzymes that can digest cellular macromolecules. The lysosome membrane helps to keep its internal compartment acidic and separates the digestive enzymes from the rest of the cell. Lysosome enzymes are made by proteins from the endoplasmic reticulum and enclosed within vesicles by the Golgi apparatus. Lysosomes are formed by budding from the Golgi complex.

Lysosome Enzymes

Lysosomes contain various hydrolytic enzymes (around 50 different enzymes) that are capable of digesting nucleic acids, polysaccharides, lipids, and proteins. The inside of a lysosome is kept acidic as the enzymes within work best in an acidic environment. If a lysosome's integrity is compromised, the enzymes would not be very harmful in the cell's neutral cytosol.

Lysosome Formation

Lysosomes are formed from the fusion of vesicles from the Golgi complex with endosomes. Endosomes are vesicles that are formed by endocytosis as a section of the plasma membrane pinches off and is internalized by the cell. In this process, extracellular material is taken up by the cell. As endosomes mature, they become known as late endosomes. Late endosomes fuse with transport vesicles from the Golgi that contain acid hydrolases. Once fused, these endosomes eventually develop into lysosomes.

Lysosome Function

Lysosomes act as the "garbage disposal" of a cell. They are active in recycling the cell's organic material and in the intracellular digestion of macromolecules. Some cells, such as white blood cells, have many more lysosomes than others. These cells destroy bacteria, dead cells, cancerous cells, and foreign matter through cell digestion. Macrophages engulf matter by phagocytosis and enclose it within a vesicle called a phagosome. Lysosomes within the macrophage fuse with the phagosome releasing their enzymes and forming what is known as a phagolysosome. The internalized material is digested within the phagolysosome. Lysosomes are also necessary for the degradation of internal cell components such as organelles. In many organisms, lysosomes are also involved in programmed cell death.

Lysosome Defects

In humans, a variety of inherited conditions can affect lysosomes. These gene mutation defects are called storage diseases and include Pompe's disease, Hurler Syndrome, and Tay-Sachs disease. People with these disorders are missing one or more of the lysosomal hydrolytic enzymes. This results in the inability of macromolecules to be properly metabolized within the body.

Similar Organelles

Like lysosomes, peroxisomes are membrane-bound organelles that contain enzymes. Peroxisome enzymes produce hydrogen peroxide as a by-product. Peroxisomes are involved in at least 50 different biochemical reactions in the body. They help to detoxify alcohol in the liver, form bile acid, and break down fats.

Eukaryotic Cell Structures

In addition to lysosomes, the following organelles and cell structures can also be found in eukaryotic cells:

• Cell membrane: Protects the integrity of the interior of the cell.
• Centrioles: Help to organize the assembly of microtubules.
• Cilia and Flagella: Aid in cellular locomotion.
• Chromosomes: Carry heredity information in the form of DNA.
• Cytoskeleton: A network of fibers that support the cell.
• Endoplasmic Reticulum: Synthesizes carbohydrates and lipids.
• Nucleus: Controls cell growth and reproduction.
• Ribosomes: Involved in protein synthesis.
• Mitochondria: Provide energy for the cell.