The endoplasmic reticulum is an organelle that is found in eukaryotic cells. If you remember from previous lessons, eukaryotic cells are cells that have a nucleus.
EXAMPLEOur cells are eukaryotic cells, so an endoplasmic reticulum is an organelle that would be found in our cells.
The endoplasmic reticulum also works closely with another organelle called the Golgi body or the Golgi apparatus. They help prep materials and get them packaged to be sent out to different parts of the cell.
The endoplasmic reticulum's role is to synthesize and package proteins and lipids in the cell. There are two parts of the endoplasmic reticulum: smooth and rough.
The endoplasmic reticulum is part of the endomembrane system, a system that makes lipids, modifies proteins, and helps to package those molecules that will be sent out to different parts of the cell wherever they're needed. The endomembrane system includes the nucleus, the endoplasmic reticulum, the Golgi apparatus, and the plasma membrane. These organelles are grouped into a system because vesicles connect them. For example, a bit of the ER's membrane will pinch off into a membrane-bound bubble (a vesicle), which will merge with the membrane of the Golgi apparatus and deliver part of the ER's contents into the Golgi apparatus. Likewise, the Golgi apparatus will send vesicles to the ER.
Surrounding the nucleus we have the nuclear envelope, which is where the endoplasmic reticulum begins. As you learn about the function of the endoplasmic reticulum, please refer to the image below.
The rough endoplasmic reticulum is attached to the nuclear envelope. The reason that you call it rough ER is because it has ribosomes attached to it.
The little dots all over the place are the ribosomes. In this part of the endoplasmic reticulum, newly formed polypeptide chains will enter, then side chains will be added onto them to help complete that protein.
The function of ribosomes uses RNA messages sent from the nucleus to build proteins. It makes sense that the part of the endoplasmic reticulum with a lot of ribosomes on it (the "rough ER") is near the nucleus: The RNA messages leave the nucleus and immediately get converted into protein by the ribosomes on the rough ER.
Proteins can act as enzymes, take part in the production and regulation of hormones, or regulate different cell functions. In the image above, the ribosomes are on the rough ER (and elsewhere in the cytoplasm). Finally, ribosomes are made up of two subunits. The parts of those ribosomes are made in the nucleus.
Further away from the nucleus, the ER has fewer ribosomes attached to it. With fewer ribosomes, this part of the ER does less protein production and more lipid production. It is called the smooth endoplasmic reticulum.
The smooth ER is called such because it does not have as many ribosomes attached to it. The smooth endoplasmic reticulum's job is to assemble lipids (fats).
Source: THIS WORK IS ADAPTED FROM SOPHIA AUTHOR AMANDA SODERLIND