Endoplasmic Reticulum (ER) – Structure, Types & Functions | PreachBio

 

Endoplasmic Reticulum (ER) – Structure, Types & Functions

🔹 Definition

The Endoplasmic Reticulum (ER) is a network of interconnected flattened sacs (cisternae) and branching tubules extending throughout the cytoplasm in eukaryotic cells. It forms a pipeline between the nucleus and cytoplasm for the synthesis, processing, and transport of biochemical compounds.

🔹 Origin & Discovery

• Discovered by: Keith R. Porter and Albert Claude (1945) using electron microscopy.

Literal meaning:

• “Endo” = inside
• “Plasmic” = cytoplasm
• “Reticulum” = network
• → ER = “network within the cytoplasm.”

🔹 Structure

• ER is continuous with the nuclear envelope, forming a single compartment with the cisternal space.
• Takes up >10% of cell volume.
• Cisternae (singular: cisterna): flattened sacs of ER lumen.
• Two main types: Rough ER (RER) and Smooth ER (SER).

1. Rough Endoplasmic Reticulum (RER)

• Surface covered with ribosomes, giving a rough appearance.
• Mainly involved in protein synthesis and processing.
• Adds chemical modifications to proteins (e.g., glycosylation) during transport.
• Proteins may be sent to Golgi apparatus for further modification.

2. Smooth Endoplasmic Reticulum (SER)

• No ribosomes on surface → smooth appearance.

Functions:

• Lipid synthesis (phospholipids, steroids).
• Carbohydrate metabolism.
• Detoxification of drugs and poisons (especially liver cells).
• Calcium storage and metabolism, especially in muscle cells for contractions.
• SER is more extensive in brain, liver, and muscle cells.

🔹 Functions of ER

1. Protein synthesis and processing (RER).
2. Lipid and carbohydrate synthesis (SER).
3. Detoxification of harmful substances (SER).
4. Calcium storage and release (SER).
5. Transport of molecules between nucleus and cytoplasm.
6. Maintaining cellular architecture via ER membrane network.

🔹 Quick Exam-Oriented Points

• ER lumen + perinuclear space = single compartment.
• RER → proteins, ribosome-bound, rough appearance.
• SER → lipids, calcium, detoxification, smooth appearance.
• ER is continuous with the nuclear envelope → efficient communication with nucleus.
• Discovered via electron microscopy (Porter & Claude, 1945).

🔹 Chemical Composition (Approximate)

• Water: 70–80%
• Proteins: 15–20% (enzymatic and structural)
• Lipids: 5–10% (membranes, lipid metabolism)
• Carbohydrates: 1–2% (glycoproteins, energy storage)

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References & Useful Links for PreachBio Users

• 3.4 – Structure of Cell (Cell Wall)
• Plasma Membrane
• Cytoplasm
• Nucleus – Structure and Functions

Endoplasmic Reticulum (ER) Quiz – 20 Marks

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