Difference Between Smooth Endoplasmic Reticulum and Rough Endoplasmic Reticulum

All living organisms found on earth are made up of cells. They are the building blocks of life. Cells are categorized into two types- eukaryotic cells and prokaryotic cells. The major difference between these two types of cells is in the presence of cell organelles. The former cell has several cell organelles present in it whereas the latter lacks these cell organelles. The endoplasmic reticulum is one such cell organelle found in every eukaryotic cell excluding some exceptions like RBCs. It performs a variety of functions in a cell and has two parts as rough endoplasmic reticulum and smooth endoplasmic reticulum.

What is an endoplasmic reticulum?

ER was discovered by Keith Porter and Claude. The word 'reticulum' in ER means ‘network’ and this word was added in its name by Porter. Its discovery was made possible due to the invention of the electron microscope. Endoplasmic Reticulum is a tubular, membranous cell organelle seen in continuity with the nuclear membrane of the nucleus in the cell. All the membranes of the ER form a network and are interconnected with each other. Endoplasmic Reticulum is a single membraned organelle and is also a part of the endomembrane system of the cell. The network formed by it is highly complex.

The endoplasmic reticulum is a cell organelle that is in charge of lipid production and protein processing. The endoplasmic reticulum (ER) is a network of linked membranous vesicles and tubules that manufacture lipids and modify proteins. The rough ER and the smooth ER, on the other hand, conduct these two roles in distinct sections of the ER. The lumen, or cisternal space, is the hollow section of the ER tubules. The ER membrane is a phospholipid bilayer packed with proteins that run parallel to the nuclear envelope.

Types of ER

Based on appearance and function, Endoplasmic Reticulum is of two types namely Smooth Endoplasmic Reticulum (SER) and Rough Endoplasmic Reticulum (RER). To understand the differences between the Smooth Endoplasmic Reticulum (SER) and Rough Endoplasmic Reticulum (RER) let us look into each subset individually. 

Rough  Endoplasmic Reticulum

It is found close to the nuclear membrane. It bears several ribosomes on itself. Due to the presence of small granular ribosomes that are present on the surface of ER  they are termed as rough ER. Ribosomes transport freshly generated proteins into the RER lumen, where proteins encounter structural changes like folding and side-chain addition. These altered proteins will be integrated into biomembranes, such as the ER membrane or that of various organelles, or released from the cell as protein hormones or enzymes. Phospholipids for cell membranes are also produced by the RER. If the phospholipids or changed proteins aren't meant to stay in the RER, they'll be transported to their final destination by transport vesicles that sprout from the membrane of the RER. The RER is common in cells that produce proteins because it is involved in altering proteins such as enzymes that will be secreted from the cell. An example of such a cell is hepatocytes.

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Structure of RER

RER has several flattened tubules that are joined with each other. They are highly dense near the nuclear membrane. These are highly convoluted tubules.

Functions of Rough Endoplasmic Reticulum

Since we have developed a basic understanding of the RER, let us look into the major functions performed by RER.

• RER helps in the formation of proteins in the cell. The presence of ribosomes is responsible for the synthesis of the proteins by the RER.

• Thus RER is found in excess in those cells where protein synthesis takes place in a large amount.

Smooth Endoplasmic Reticulum

RER continues towards the periphery of the cell to form the SER. Ribosomes are absent on the surface of SER which is why it has a smooth appearance. Thus it's called Smooth Endoplasmic Reticulum. Unlike RER, SER is a meshwork of fine tubules. It also consists of vesicles. It is less extensive than RER The smooth endoplasmic reticulum (SER) is connected to the RER.

Functions of SER

Let us look into some of the important functions of the SER mentioned below.

• The smooth endoplasmic reticulum performs the function of the synthesis of lipids. Thus they are present in the cells of those organs where steroid secretions take place like an ovary.

• SER cannot synthesize proteins as it lacks ribosomes which are considered as the sites of protein synthesis.

• SER also helps in the process of detoxification in the liver.

Overall functions of endoplasmic reticulum

The functions of SER and RER jointly give a complete idea of the functions performed by the ER as a whole. These functions are as follows-

• ER helps in membrane biogenesis.

• This process refers to the formation of the cell membrane. It is widely known that the cell membrane is made up of lipids and proteins. These lipids and proteins are provided by the combined work of RER and SER. 

• ER performs many mechanical functions of the cell thus providing the cell with mechanical support.

• The large surface of the ER helps in the exchange of various materials in the cell by diffusion and active transport.

• It also helps in the circulation of substances within the cell.

• It is also responsible for the formation of certain cell organelles like lysosomes.

Difference between RER and SER

Since we have understood the structure and functions let us look into the differences. The major differences are mentioned below in the tabular form.

Fun Fact 

The endoplasmic reticulum of muscle cells is known as the Sarcoplasmic reticulum. They are considered the storehouse of calcium ions.

In the conclusion of the article, we have learned about the endoplasmic reticulum. We have also learned about the differences between RER and SER.