The rough endoplasmic reticulum comprises the endomembrane system. As the name suggests this reticulum appears rough when viewed under a microscope. This is because the rough endoplasmic reticulum contains ribosomes and these are responsible for its rough appearance. As the rough endoplasmic reticulum has ribosomes attached to it, so they are a site of protein synthesis and the rough endoplasmic reticulum works the same way. One more important function of the rough endoplasmic reticulum is that it helps in giving rise to the smooth endoplasmic reticulum.
We have two types of cells in nature, they are prokaryotic and eukaryotic. The eukaryotic cells have the presence of a true nucleus. The prokaryotic cells do not possess a true nucleus. The prokaryotic cells are thought to be primitive cells. The eukaryotic cells have the presence of membrane-bound organelles. All the membrane-bound organelles have distinct structures and functions. The endomembrane system comprises the organelles that work in a coordinated manner. The mitochondria, chloroplast and peroxisomes do not work in a coordinated manner to any other organelle hence, they are not a part of the endomembrane system. We will study the function of smooth endoplasmic reticulum, the function of the rough endoplasmic reticulum, and the structure of endoplasmic reticulum.
In this paragraph, we will learn about the function and structure of endoplasmic reticulum. It is a network of reticulum that are just tiny tubular structures that are scattered around in the cytoplasm. The endoplasmic reticulum is formed by three types of structures that are cisternae, tubules and vesicles.
They are long and flattened structures. They also have sac-like and interconnected structures. The cells that are actively involved in protein synthesis is the place where we can find out these cisterns. They are also found in cells that have very active synthetic roles. Cells of the pancreas and the brain are the examples where the cisternae are found. These cisternae have large subunits of ribosomes. The large subunit of ribosomes is the 60S.
These form the reticular structure. Some of them have branches and some of them are unbranched. They form the reticular system along with the cisternae and vesicles. No ribosomes are present on them. They are found in abundance where the cells are involved in lipid and sterol synthesis.
The vesicles are membrane-bound vacuolar structures. They are oval. In the pancreatic cells, they are found in abundance. The vesicles are the one and only endoplasmic reticular structures that are found in the spermatocytes.
The endoplasmic reticulum helps in dividing the intracellular space into two distinct compartments. Those compartments are:
This compartment forms and encloses the internal space. It is enclosed by the endoplasmic reticulum.
This space is present outside the endoplasmic reticulum.
Types of Endoplasmic Reticulum
The endoplasmic reticulum is divided into two types. They are divided on the basis of the presence or absence of ribosomes on their surface. They are:
Smooth Endoplasmic Reticulum
Here we will learn about the function of smooth endoplasmic reticulum. This reticulum is free from ribosomes. It is also known as the agranular reticulum. Smooth tubular structures appear when it is viewed under the microscope. Our muscle cells have rich amounts of the smooth endoplasmic reticulum. When it is present in muscles, it is known as the sarcoplasmic reticulum.
The Function of Smooth Endoplasmic Reticulum are:
They help in the synthesis of lipids and steroids.
They help in the detoxification of drugs.
The synthetic products of the rough endoplasmic reticulum are passed onto the Golgi complex via the smooth endoplasmic reticulum.
They help in muscle contraction. This is done by the release and uptake of calcium ions.
Rough Endoplasmic Reticulum
The rough endoplasmic reticulum contains ribosomes. The ribosomes are present on their surface. When it is seen under an electron microscope, rough patches appear therefore it is known as the rough endoplasmic reticulum. It is also known as granular reticulum. They are extensive and are present in continuity with the outer membrane of the nucleus. The rough endoplasmic reticulum contains two types of glycoproteins are Ribophorin-I and ribophorin-II. These are present for the attachment of ribosomal subunits. Mainly it is present for the attachment of the 60S subunit of 80S ribosomes.
The Functions of the Rough Endoplasmic Reticulum are:
As they have the presence of ribosomes, so they are the site of protein synthesis. As they are sites of protein synthesis, they are found at places that are actively involved in protein synthesis. Not just synthesis, but they are present in sites of secretion of proteins.
They are responsible for giving rise to the smooth endoplasmic reticulum.
They help in providing the precursors of the enzymes that are required for the formation of Golgi complexes.
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Figure: Rough endoplasmic reticulum structure