Endoplasmic reticulum

The Endoplasmic Reticulum (ER) is a type of organelle found in eukaryotic cells that forms an interconnected network of flattened, membrane-enclosed sacs or tube-like structures known as cisternae. The membranes of the ER are continuous with the nuclear envelope that surrounds the nucleus.

Structure

The endoplasmic reticulum membrane system can be morphologically divided into two structures—cisternae and the reticular network. Cisternae are flattened, membrane-enclosed sacs, while the reticular network is a series of interconnected tubules.

Functions

The endoplasmic reticulum serves many general functions, including the facilitation of protein synthesis and the conduction of lipids. It also has a more specialized function in cells such as those producing steroid hormones and those involved in the detoxification of drugs and poisons.

Protein synthesis and transport

The ER is the site of the translation of messenger RNA (mRNA) into proteins. These proteins include those that will remain within the ER, as well as those that are transported to other parts of the cell.

Lipid synthesis and transport

The ER is also involved in the synthesis of lipids. It is the site of the production of all cellular lipids, including phospholipids and cholesterol, and the transport of these lipids to their proper locations within the cell.

Types of Endoplasmic Reticulum

There are two types of ER: rough and smooth. The Rough Endoplasmic Reticulum (RER) is so named because it is studded with ribosomes, the sites of protein synthesis. The Smooth Endoplasmic Reticulum (SER) functions in lipid manufacture and metabolism, the production of steroid hormones, and detoxification.

See Also

• Cell (biology)
• Organelle
• Protein synthesis
• Lipid
• Steroid hormone
• Detoxification

• 
  Endoplasmic reticulum illustration
• 
  Diagram of nucleus, endoplasmic reticulum, and Golgi apparatus
• 
  Animation of protein translation
• 
  Labeled diagram of endoplasmic reticulum
• 
  Skeletal muscle illustration
• 
  CaATiER model