Endoplasmic Reticulum: The endoplasmic reticulum (ER) is a large, dynamic structure that serves many roles in the cell including calcium storage, protein synthesis and lipid metabolism. The diverse functions of the ER are performed by distinct domains; consisting of tubules, sheets and the nuclear envelope.

Types of Endoplasmic Reticulum

There are two types of endoplasmic reticulum:

• Rough endoplasmic reticulum (rough ER): This is an extensive organelle composed of greatly convoluted but flattish sealed sacs, which are contiguous with the nuclear membrane. It is called ‘rough’ endoplasmic reticulum because it is studded on its outer surface (the surface in contact with the cytosol) with ribosomes. These are called membrane bound ribosomes and are firmly attached to the outer cytosolic side of the ER About 13 million ribosomes are present on the RER in the average liver cell. Rough ER is found throughout the cell but the density is higher near the nucleus and the Golgi apparatus.
• Smooth endoplasmic reticulum (smooth ER): Smooth ER is more tubular than rough ER and forms an interconnecting network sub-compartment of ER. It is found fairly evenly distributed throughout the cytoplasm.
  It is not studded with ribosomes hence ‘smooth’ ER. Smooth ER is devoted almost exclusively to the manufacture of lipids and in some cases to the metabolism of them and associated products. In liver cells for example smooth ER enables glycogen that is stored as granules on the external surface of smooth ER to be broken down to glucose. Smooth ER is also involved in the production of steroid hormones in the adrenal cortex and endocrine glands.

Structure of Endoplasmic Reticulum

Rough Endoplasmic Reticulum Structure

• The rough endoplasmic reticulum is named so because of its appearance.
• It is a series of connected flattened sacs having several ribosomes on its outer surface, hence the name.
• It synthesizes and secretes proteins in the liver, hormones and other substances in the glands.
• Rough ER is prominent in cells where protein synthesis happens (such as hepatocytes)

Smooth Endoplasmic Reticulum Structure

• The smooth endoplasmic reticulum, on the other hand, does not have ribosomes.
• The smooth endoplasmic reticulum has a tubular form.
• It participates in the production of phospholipids, the chief lipids in cell membranes and are essential in the process of metabolism.
• Smooth ER transports the products of the rough ER to other cellular organelles, especially the Golgi apparatus.

Functions of Endoplasmic Reticulum

• Endoplasmic reticulum function includes the Golgi apparatus, lysosomes, plasma membrane, etc.
• In addition, it is responsible for transport. Transport of carbohydrates and proteins to another organelle.
• They provide a wide area for cellular reactions.
• Furthermore, it helps in formation. Formation of the nuclear membrane at the time of cell division.
• In the skeletal framework formation, they play an important role.
• Most noteworthy, it plays an important role in the synthesis of lipids, glycogen, proteins. Also, other steroids like progesterone, testosterone, and cholesterols, etc.

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By Team Learning Mantras