Endoplasmic ReticulumIn Journey into the Cell, we looked at the structure of the two major types of cells: prokaryotic and eukaryotic cells. Now we turn our attention to the endoplasmic reticulum (ER).
The endoplasmic reticulum is a network of tubules and flattened sacs that serve a variety of functions in the cell. There are two regions of the ER that differ in both structure and function. One region is called rough ER because it has ribosomes attached to the cytoplasmic side of the membrane. The other region is called smooth ER because it lacks attached ribosomes. Typically, the smooth ER is a tubule network and the rough ER is a series of flattened sacs. The space inside of the ER is called the lumen. The ER is very extensive extending from the cell membrane through the cytoplasm and forming a continuous connection with the nuclear envelope. Since the ER is connected with the nuclear envelope, the lumen of the ER and the space inside the nuclear envelope are part of the same compartment.
Rough Endoplasmic ReticulumThe rough endoplasmic reticulum manufactures membranes and secretory proteins. In certain leukocytes (white blood cells), the rough ER produces antibodies. In pancreatic cells, the rough ER produces insulin. The rough and smooth ER are usually interconnected and the proteins and membranes made by the rough ER move into the smooth ER to be transferred to other locations.
Smooth Endoplasmic ReticulumThe smooth ER has a wide range of functions including carbohydrate and lipid synthesis. It serves as a transitional area for vesicles that transport ER products to various destinations. In liver cells the smooth ER produces enzymes that help to detoxify certain compounds. In muscles the smooth ER assists in the contraction of muscle cells, and in brain cells it synthesizes male and female hormones.
Eukaryotic Cell StructuresThe endoplasmic reticulum is only one component of a cell. The following cell structures can also be found in a typical animal eukaryotic cell:
- Centrioles - help to organize the assembly of microtubules.
- Chromosomes - house cellular DNA.
- Cilia and Flagella - aid in cellular locomotion.
- Cell Membrane - protects the integrity of the interior of the cell.
- Golgi Complex - manufactures, stores and ships certain cellular products.
- Lysosomes - digest cellular macromolecules.
- Mitochondria - provide energy for the cell.
- Nucleus - controls cell growth and reproduction.
- Peroxisomes - detoxify alcohol, form bile acid, and use oxygen to break down fats.
- Ribosomes - responsible for protein production via translation.