What are Organelles?

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Organelles are small structures that perform specific functions within cells, with the most important being the nucleus, endoplasmic reticulum, Golgi apparatus, mitochondria, and chloroplasts. Each organelle has a unique task, such as producing energy or proteins. Organelles evolved to isolate complex chemical reactions within cells, and their structure allows for protection and regulation of chemical conditions. Mitochondria produce ATP, the main source of energy for animal and fungal cells, while chloroplasts use photosynthesis to produce glucose in plants and algae. Organelles can communicate with each other and dysfunction can lead to severe symptoms and diseases, such as cystic fibrosis, Alzheimer’s, and mitochondrial disorders.

Organelles are tiny structures that perform very specific functions within cells. The term is a reference to organs, likening the way these structures operate in cells to the way organs function in the body. Different organelles can be found within various types of plant, animal and bacterial cells. Each has its own important task, such as producing energy or producing proteins.


These structures have a wide range of functions, most of which are tasks critical to the life of the cell. The most important structures are the nucleus, the endoplasmic reticulum (ER), the Golgi apparatus, the mitochondria and the chloroplasts. Each of these tend to be found in specific areas of the cells. Typically, the nucleus is located near the center, with the ER and Golgi located nearby, and the remaining organelles spread throughout the cell.

The type and number of organelles present within a cell varies according to the purpose of the cell. For example, nearly all plant and animal cells contain a nucleus, with the notable exception of mature red blood cells, which contain no organelles or genetic material. Another example is that muscle cells typically have far more mitochondria than other cell types, because more energy is required for muscle cells to function effectively.


Researchers believe that the general reason organelles evolved is that cells benefit from the isolation of the many complex chemical reactions that occur within them. Inside plant and animal cells, each is enclosed in its own membrane, which helps the unit function. A major benefit of this protection is that, within a membrane-enclosed unit, chemical conditions such as pH can be changed without affecting the entire cell. Likewise, the contents of each are isolated from what is happening inside the cell at large.

Some organelles are so large that their shape and surface area can be seen under a light microscope. These include the mitochondria and Golgi, as well as the cell nucleus. However, an electron microscope is needed to look at them more closely. Only when these structures could be examined via electron microscopy did researchers begin to understand how they worked.

Energy production
Mitochondria are responsible for supplying usable energy to cells. They are found in most complex organisms, including fungi, plants and animals. The main function of these structures is to produce a molecule called adenosine triphosphate, or ATP, which is the main source of energy in animal and fungal cells and a secondary source for plants. Mitochondria also have additional functions, including regulating cellular metabolism and storing calcium.
Some organelles are found only within a specific type of organism. The best-known example is chloroplasts, which are found only in plant and algae cells. Chloroplasts use sunlight to produce glucose through the process known as photosynthesis. Another example is the carboxysome, which is found only in some bacterial species. Carboxisomes allow bacteria to turn carbon into organic molecules that they can use for energy.

Protein production and DNA interactions
Many organelles are able to communicate with each other, either by their proximity or via chemical signaling. For example, the endoplasmic reticulum connects to the Golgi apparatus and both of these units are involved in the production of new proteins. New proteins are produced in the endoplasmic reticulum and from there they travel to the Golgi, where they are modified and packaged for transport to other places in the cell.
Another example of this communication is the one that occurs between the nucleus of a cell and the other organelles inside it. Although the nucleus and the DNA it contains do not physically connect with other cellular structures, it communicates with the rest of the cell through protein signaling molecules. The membrane that surrounds the nucleus controls what can enter and exit the structure, limiting traffic to special proteins that can interact with DNA strands.

Just as larger organs can be affected by health issues, individual organelles can also be prone to medical conditions and congenital disorders. These structures are so essential to cellular function that diseases affecting them often cause severe symptoms and, in some cases, are fatal. Dysfunction can have far-reaching and unexpected results.
Endoplasmic reticulum dysfunction has been implicated in conditions such as cystic fibrosis and Alzheimer’s, Huntington’s and Parkinson’s diseases. In any case, the cellular dysfunction that puts stress on the emergency room is thought to contribute to the symptoms that develop. Diseases that affect the Golgi include congenital disorders that cause liver disease, mental disability, and seizures, and typically cause death before a child reaches the age of two.
A large family of conditions known as mitochondrial disorders can cause everything from digestive problems to blindness, depending on the specific nature of the disorder a person has. These conditions can be difficult to treat, as they usually involve birth defects that cause damage to all organelles involved in a given cell type.

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