What are Cellular Organelles?
Organelles are membrane-bound structures that carry out different functions inside a eukaryotic cell.
The most basic organelle is the nucleus, which is a membrane that contains the cell’s genetic code. You can think of the nucleus as the instruction book for the cell; the DNA inside contains all the information the cell needs to function properly. Having genetic information enclosed inside the nucleus is what separates eukaryotic cells from prokaryotic cells.
Mitochondria are organelles found in animal, plant, and fungi cells. Mitochondria convert sugar into energy that the cell can use to do its job. Plant cells have another kind of organelle called chloroplasts, which use sunlight to create sugar that the plant can break down for energy.
Mitochondria and chloroplasts are particularly interesting organelles, because many scientists think that they may have originally come from free-living prokaryotic cells. The idea is that a primitive eukaryotic cell engulfed a prokaryotic cell and, instead of digesting it, allowed the smaller cell to stay inside it as long as the cell provided energy to its host. A symbiotic relationship was formed, and the prokaryotic cell eventually became an organelle within the larger eukaryotic cell.
This idea is supported by the fact that mitochondria and chloroplasts have their own DNA and are in some ways very similar to the free-living unicellular organisms they may have originated from.
Another important organelle found in nearly all eukaryotic cells is the endoplasmic reticulum. The endoplasmic reticulum is responsible for manufacturing proteins based on the instructions found in the nucleus.
There are many other organelles found within a cell, which carry out a host of functions from storage to transport to assiting with the manufacture of proteins. Different cells may have different types of organelles depending on the demands of their job.
For example, cells that secrete hormones or enzymes (like pancreas or liver cells) may have large storage organelles and a big endoplasmic reticulum to handle the export of so many substances. Red blood cells, on the other hand, completely lack mitochondria and an endoplasmic reticulum, because their one and only job is to carry oxygen.
Clker-Free-Vector-Images (artist). (2012).View Cell Information [digital art]. Retrieved from