In addition to their role as the digestive component and organelle-recycling facility of animal cells, lysosomes are considered to be parts of the endomembrane system. Lysosomes also use their hydrolytic enzymes to destroy pathogens disease-causing organisms that might enter the cell. In a process known as phagocytosis or endocytosis, a section of the plasma membrane of the macrophage invaginates folds in and engulfs a pathogen.
The invaginated section, with the pathogen inside, then pinches itself off from the plasma membrane and becomes a vesicle. Tay-Sachs disease, for example, is caused by a genetic defect that prevents the formation of an essential enzyme that breaks down complex lipids called gangliosides. An accumulation of these lipids damages the nervous system, causes mental retardation, and death in early childhood. Also, arthritis inflammation and pain are related to the escape of lysosome enzymes.
License Info. Image Use. Custom Photos. Site Info. Contact Us. The Galleries:. Photo Gallery. Lysosomes are involved with various cell processes. They break down excess or worn-out cell parts. They may be used to destroy invading viruses and bacteria. If the cell is damaged beyond repair, lysosomes can help it to self-destruct in a process called programmed cell death, or apoptosis.
Now, the lysosome is a specific type of organelle that's very acidic. Ribosomes transfer their newly synthesized proteins into the lumen of the RER where they undergo structural modifications, such as folding or the acquisition of side chains. These modified proteins will be incorporated into cellular membranes—the membrane of the ER or those of other organelles —or secreted from the cell such as protein hormones, enzymes.
The RER also makes phospholipids for cellular membranes. Since the RER is engaged in modifying proteins such as enzymes, for example that will be secreted from the cell, the RER is abundant in cells that secrete proteins. This is the case with cells of the liver, for example.
Rough Endoplasmic Reticulum : This transmission electron micrograph shows the rough endoplasmic reticulum and other organelles in a pancreatic cell. The smooth endoplasmic reticulum SER is continuous with the RER but has few or no ribosomes on its cytoplasmic surface. Functions of the SER include synthesis of carbohydrates, lipids, and steroid hormones; detoxification of medications and poisons; and storage of calcium ions.
In muscle cells, a specialized SER called the sarcoplasmic reticulum is responsible for storage of the calcium ions that are needed to trigger the coordinated contractions of the muscle cells. The Golgi apparatus sorts and packages materials before they leave the cell to ensure they arrive at the proper destination. We have already mentioned that vesicles can bud from the ER and transport their contents elsewhere, but where do the vesicles go? Before reaching their final destination, the lipids or proteins within the transport vesicles still need to be sorted, packaged, and tagged so that they wind up in the right place.
Sorting, tagging, packaging, and distribution of lipids and proteins takes place in the Golgi apparatus also called the Golgi body , a series of flattened membranes. The Golgi apparatus sorts and packages cellular products : The Golgi apparatus in this white blood cell is visible as a stack of semicircular, flattened rings in the lower portion of the image. Several vesicles can be seen near the Golgi apparatus.
The receiving side of the Golgi apparatus is called the cis face. The opposite side is called the trans face. The transport vesicles that formed from the ER travel to the cis face, fuse with it, and empty their contents into the lumen of the Golgi apparatus. As the proteins and lipids travel through the Golgi, they undergo further modifications that allow them to be sorted.
The most frequent modification is the addition of short chains of sugar molecules. These newly-modified proteins and lipids are then tagged with phosphate groups or other small molecules so that they can be routed to their proper destinations. Finally, the modified and tagged proteins are packaged into secretory vesicles that bud from the trans face of the Golgi.
While some of these vesicles deposit their contents into other parts of the cell where they will be used, other secretory vesicles fuse with the plasma membrane and release their contents outside the cell. In another example of form following function, cells that engage in a great deal of secretory activity such as cells of the salivary glands that secrete digestive enzymes or cells of the immune system that secrete antibodies have an abundance of Golgi. In plant cells, the Golgi apparatus has the additional role of synthesizing polysaccharides, some of which are incorporated into the cell wall and some of which are used in other parts of the cell.
Lysosomes are organelles that digest macromolecules, repair cell membranes, and respond to foreign substances entering the cell. When food is eaten or absorbed by the cell, the lysosome releases its enzymes to break down complex molecules including sugars and proteins into usable energy needed by the cell to survive.
In addition to their role as the digestive component and organelle-recycling facility of animal cells, lysosomes are considered to be parts of the endomembrane system. Lysosomes also use their hydrolytic enzymes to destroy pathogens disease-causing organisms that might enter the cell. In a process known as phagocytosis or endocytosis, a section of the plasma membrane of the macrophage invaginates folds in and engulfs a pathogen. The invaginated section, with the pathogen inside, then pinches itself off from the plasma membrane and becomes a vesicle.
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