The endoplasmic reticulum is an organelle composed of a series of folded tubes, called cisternae, which are connected together. These tubes are important in helping the endoplasmic reticulum make, store and ship molecules the cell needs to function. There are three different types of endoplasmic reticulum (ER):
- The Rough ER is rough because its surface is dotted with ribosomes used to make proteins. When proteins are made, they enter the rough ER as a string of amino acids that needs to be folded precisely to perform its function. This is similar to how a sheet of paper can be folded according to specific instructions to make any shape in origami. The rough ER is also important in tagging proteins with an address to send them to the right part of the cell. Pancreatic cells have lots of rough ER.
- The Smooth ER has no ribosomes on its surface and is important in making and storing other molecules the cell needs. These include fats and hormones. The smooth ER is also important in breaking down toxins. Cells in the liver, testes and ovaries have lots of smooth ER.
- The Sarcoplasmic reticulum is a special type of ER found in muscle cells. It is special because it doesn’t make molecules but instead stores lots of calcium for use during muscle contraction. Calcium is necessary for muscle contraction and so they need to store it for future use, this is where the sarcoplasmic reticulum comes in handy.
The ER ships molecules by working together with the cells highway system, called the cytoskeleton. The ER can pinch off little bubbles from its surface that contain the proteins or other molecules and send that bubble along the cytoskeleton to any other part inside or outside of the cell.
See below for an endoplasmic reticulum: