Endoplasmic Reticulum, Definition, Types, Structure and Function

The endoplasmic reticulum  (ER) is an important organelle found in eukaryotic cells that helps in making and transporting proteins and lipids. It plays a key role in the overall function of cells. Understanding the ER is essential for students preparing for the NEET Exam , as it is included in the NEET syllabus .

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Definition of  Endoplasmic Reticulum

Types of  Endoplasmic Reticulum

Rough Endoplasmic Reticulum

Smooth Endoplasmic Reticulum

Difference Between Rough and Smooth Endoplasmic Reticulum

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Structure of  Endoplasmic Reticulum

Components of the Endoplasmic Reticulum

• Cisternae are elongated, flattened, and unbranched sac-like structures.
• They are organized in parallel bundles, providing a large surface area for various functions.
• Cisternae typically range from 40 to 50 micrometers in diameter.
• The rough endoplasmic reticulum (RER) has ribosomes attached to its surface, facilitating protein synthesis.
• Cisternae are primarily involved in the synthesis and modification of proteins destined for secretion or for use in the cell membrane.

• Vesicles are small, rounded, or ovoid structures.
• They vary in size, ranging from 25 to 500 microns.
• Vesicles are found abundantly in cells like pancreatic cells and are often located at the ends of cisternae and tubules.
• Vesicles transport proteins and lipids between different compartments of the cell, including to the Golgi apparatus and plasma membrane.

• Tubules are smooth-walled, branched, tubular structures that can have various shapes.
• They typically range from 50 to 100 microns in diameter.
• Tubules are usually found in non-secretory cells, such as striated muscle cells.
• Tubules are involved in lipid synthesis and detoxification processes, serving as pathways for the transport of biomolecules.

Endoplasmic Reticulum Diagram

Function of  Endoplasmic Reticulum

• Transportation : The ER serves as a transportation network within the cell, moving proteins and other molecules to different parts of the cell.
• Membrane Structure : It forms tubules, sheets, and the nuclear envelope, providing structure and a surface for biochemical reactions within the cell.
• Calcium Storage : The ER acts as a reservoir for calcium ions (Ca2+), which are important for various cellular processes, including muscle contractions and cell signaling.
• Glycogen Synthesis : The ER also assists in the creation and storage of glycogen, a form of stored energy in cells.
• Protein Synthesis : The rough endoplasmic reticulum (RER) is the site where proteins are made. Ribosomes attach to the surface of the RER, helping in the production of proteins that are either secreted from the cell or become part of the cell membrane.
• Lipid Synthesis : The smooth endoplasmic reticulum (SER) plays a key role in making lipids (fats), which are important for the structure of cell membranes and energy storage.
• Synthesis of Steroids : The SER helps in the production of steroids like hormones, including progesterone, testosterone, and cholesterol, which are essential for various body functions.

Endoplasmic Reticulum MCQs

Q1. Which side in a cell is luminal and extraluminal compartments situated respectively?

Q2. From the following events, which do NOT occur in rough endoplasmic reticulum?

Q3. Identify the wrong statement with respect to ER:

Endoplasmic Reticulum MCQs Answers