Structure and Function of the Endoplasmic ReticulumEdit
The Endoplasmic Reticulum (ER) consists of a series of flattened sacs that make up a network of membrane tubules, called cisternae. The ER’s membrane is continuous with the outer membrane of the nuclear envelope. The space enclosed by the ER membranes is called the ER cisternal or luminal space and sometimes this can take up as much as approximately 10% of the total cell volume (Alberts et al 2008, p.723).
There are two main parts to the ER:
- 1) The Smooth ER (SER)
- 2) The Rough ER (RER)
The smooth ER (SER) carries out the synthesis of steroid hormones, detoxification of harmful organic compounds and in muscle cells it is specialised to regulate the release of Ca2+ ions. It can be distinguished from the RER due to the lack of ribosomes on its outer membrane.
The rough ER (RER) is the part of the ER that processes proteins destined for exportation to the exterior of the cell. Within its luminal space it also processes most transmembrane proteins, as well as producing new membrane material used in the enlargement of all the cell’s membranes before cell division. (Madigan et al 2009, p.522) It is dotted with ribosomes since they insert the polypeptide into the ER and begin the biosynthesis pathway. This will be the part that is mainly refered to in this wiki.Usually the ER consists of a mixture of rough and smooth ER but in some cells, such as pancreatic cells and hepatocytes, noticeably different ratios of smooth and rough exist depending on the purpose of the cell.