Smooth Endoplasmic Reticulum

We all know that cells are the building blocks of life, as they are the basic unit of any living being. There are two types of cells, which differ in various aspects - prokaryotic cells and eukaryotic cells. The most important difference between a prokaryotic and an eukaryotic cell is the absence of true nucleus in the former. While prokaryotic cells are found in some microscopic organisms and bacteria; animals, plants, fungi, etc., have eukaryotic cells. Eukaryotic cells are much larger in size as compared to prokaryotic cells. There are many other distinctions between these two types of cells. Endoplasmic reticulum is one such cell organelle which is found to be absent in prokaryotic cells, but, according to some recent research, it is claimed that some of these cells have organelles resembling endoplasmic reticulum. However, this article deals with endoplasmic reticulum, as found in eukaryotic cells.


What is Endoplasmic Reticulum?

Endoplasmic reticulum in eukaryotic cells is a complex network of membranes, which possess tubules and sacs (cisternae). All these sacs and tubules are interconnected by a single membrane, which is continuous, so that the endoplasmic reticulum has a single, large, internal space, which is highly twisted and complex. This internal space, termed as the cisternal space, is also continuous, like the membranes, which separate the cisternal space from the cytosol (intracellular fluid). The cisternal space is also continuous with the perinuclear space, which is the space between the inner and outer nuclear membranes (nuclear membranes cover the nucleus of a cell, which carries the genetic material). The function and the structure of this cell organelle depend on the type of cell and the type of endoplasmic reticulum. There are three different types of endoplasmic reticulum - rough endoplasmic reticulum, smooth endoplasmic reticulum, and sarcoplasmic reticulum. In most cells, the endoplasmic reticulum consists of both rough and smooth types, which are continuous in nature. Rough endoplasmic reticulum got its name from its appearance. It is studded with ribosomes and so, it appears rough. Smooth endoplasmic reticulum lacks ribosomes on its surface and is smooth in appearance. The third and last type, called sarcoplasmic reticulum, is a type of smooth endoplasmic reticulum, which is found in smooth and striated muscles.

Smooth Endoplasmic Reticulum Facts

The two regions of an endoplasmic reticulum, called smooth and rough endoplasmic reticulum, differ in both structure and function. In general, the rough endoplasmic reticulum is responsible for protein synthesis, as it contains ribosomes. In case of pancreatic cells, the rough endoplasmic reticulum manufactures insulin. In leukocytes or white blood cells, antibodies are produced by the rough endoplasmic reticulum. These proteins are later transferred to the golgi apparatus or out of the cell. Smooth endoplasmic reticulum function includes the transportation of the proteins manufactured by the rough endoplasmic reticulum. Smooth endoplasmic reticulum is a small part of the endoplasmic reticulum, but is very prominent in some cells, like, those in the liver, adrenal cortex, and muscles. Let us take a look at the various aspects of smooth endoplasmic reticulum function.

Smooth endoplasmic reticulum, which is found in various types of plant and animal cells, is assigned with different functions, as per the type of the cell. Smooth endoplasmic reticulum functions include carbohydrate metabolism, regulation of calcium ions, synthesis of steroids and lipids, drug detoxification, metabolism of steroids, etc. In case of muscle cells, the smooth endoplasmic reticulum stores calcium, which is released during contraction of the muscles. This cell organelle has the function of detoxification in liver cells. Smooth endoplasmic reticulum function involves the transportation of newly synthesized proteins to other locations in the cell or outside the cell. This is achieved through a process called budding, wherein the small vesicles, which contain proteins, are detached from the smooth endoplasmic reticulum and are carried to other locations. This cell organelle also aids in converting glucose-6-phosphate to glucose, which is an important step in gluconeogenesis. Smooth endoplasmic reticulum in plant cells may connect between cells through plasmodesmata.

Now, you know more about smooth endoplasmic reticulum, which plays an important role in various metabolic processes. Its surface area is also used for the action or storage of important enzymes.