By Jenny

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Disposal and Recycling Units of the Cell

Christian de Duve was a Belgian researcher who discovered lysosomes in 1949. He discovered them when he homogenized some animal cells into various components by running them through an ultracentrifuge. After a few days the level of a few enzymes rose significantly implying that they were segregated in the cell and had not attacked any part of the cell before they were broken down.

Lysosomes are membrane bound vesicles containing various hydrolytic enzymes necessary for digesting certain material in a cell. Lysosomes contain an ionic pump which maintains a highly acidic pH.

Lysosomes have 2 main roles:

  1. To digest macromolecules which enter the cell- They are like sacs which contain around forty digestive enzymes. The lysosomes infuse with vesicles of engulfed material and release the digestive enzymes to break up the material. The large molecules of food are broken down into smaller particles. The products diffuse through the lysosomes' membrane and are distributed throughout the rest of the cell. The products serve as building blocks of new materials.
  2. To breakdown old nonfunctioning organelle that out lived their usefulness- Cells fail to restore themselves causing them to age. Because of this lysosomes are needed to rid the cell of these unneeded materials that are occupying space in the cell. In stressed or dying cells' membrane, this component of the cell denigrates material, releasing the destructive lysosomal enzymes into the cytoplasm. Here they digest all organelles and speed up the cells' death by this process of autolysis (self-digestion). The products are recycled and reused to compose new parts of cells.

Lysosomes are formed by the Golgi apparatus. There are primary and secondary lysosomes. The primary are formed on the rough ER (endoplasmic reticulum). The secondary lysosomes are formed on the smooth ER by following the phagocytosis (process of taking solid materials into cells). Phagosomes fuse with lysosomes and work as one digestive vacuole. Lysosomal enzymes are released into this vacuole in order to digest the bacteria or other materials. Small molecules which are the result leave the vacuole through its membrane and are used to make new molecules. The indigestible materials are deposited outside the cell.

Diseases: There are many diseases related to the malfunctioning of lysosomes. There are fifty overall. They are characterized by specific enzyme deficiencies. These diseases show characteristic patterns of the accumulation of polysaccharides or lipids in the tissues of nerve cells, muscle, liver, or spleen. Some of these diseases are arthritis, Hurler's syndrome, Tay-sachs, Pompe's disease, cystic fibroses, silicosis, asbestosis, and lysosomal storage disease.


In 1965, Christian de Duve and his colleagues found other enzymes containing organelle. They called these peroxisomes because they seemed to generate and break down hydrogen peroxide.

Peroxisomes, also known as microbodies, and they are self replicating cells containing oxidative enzymes. They are similar to lysosomes. Their enzymes have two functions; to convert fats to carbohydrates and to detoxify potentially harmful molecules which form in the cell.

Peroxisomes, in contrast to lysosomes, are produced only on the smooth ER system. They are found in the cytoplasm of many eukaryotic cells as well as prokaryotic cells, microorganisms, and plant cells. They are very active in yeast, protozoans, kidney cells, and mammailain cells.

Peroxisomes are permeable. This allows many small molecules to enter easily.

The enzymes of peroxisomes remove hydrogen atoms from small molecules and joins them to oxygen creating hydrogen peroxide. They consume up to twenty percent of the oxygen in the liver cell. The peroxisomal enzyme catalase uses this oxygen to convert hydrogen peroxide to water and oxygen neutralizing it. In the liver this method is used to break down molecules of alcohol into substances that can be eliminated from the body.

Diseases: The rare fatal genetic disorder Zellweger's syndrome is the result of malformed peroxisomes. This indicates peroxisomes do have an important role in healthy cells.

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Parts of The Cell