Notes on Endoplasmic Reticulum (ER)

Introduction to Cells

• 1665: Robert Hooke discovered cells in cork using a microscope; named them "cells" (derived from Latin "cella" - simple room).
• Hooke did not fully understand the function of cells.

Development of Cell Theory

• 1838: Matthias Schleiden and Theodor Schwann proposed cell theory:
  • All plants and animals are made of cells.
  • Cells contain a nucleus.

Discovery of the Endoplasmic Reticulum

• 1897: Charles Garnier identified the structure, originally called "ergastoplasm."
• 1953: Keith Porter renamed it to "Endoplasmic Reticulum (ER)" to reflect the tubular network.
• The understanding of ER functions is ongoing.

Functions of the Endoplasmic Reticulum

• Main Functions:
  • Produces, processes, and secretes proteins.
  • Storage for calcium.
  • Essential for lipid and steroid production.

Structure of the Endoplasmic Reticulum

• The ER consists of:
  • Interconnected flattened sheets (cisternae).
  • Branching tubules made of phospholipid membranes.
  • Continuous with the nuclear membrane and cell membrane.
• Classification:
  • Rough Endoplasmic Reticulum (RER):
    • Contains membrane-bound ribosomes (60% of ER).
    • Plays a key role in protein synthesis.
  • Smooth Endoplasmic Reticulum (SER):
    • Lacks ribosomes (40% of ER).
    • More complex structure, involved in lipid synthesis and detoxification.

Ribosomes

• Function: Site for protein synthesis (translation).
• Composed of two subunits (large and small) containing rRNA and proteins.

Rough Endoplasmic Reticulum Details

• Lumen: Space inside RER is 20-30 nm wide.
• Protein synthesis occurs here, proteins are modified and released.
• Proteins are critical for various cell functions (signaling, DNA repair, etc.).

Smooth Endoplasmic Reticulum Details

• Lumen: Space inside SER is 30-60 nm wide.
• Functions vary by cell type:
  • Muscle cells: Sarcoplasmic reticulum regulates calcium for muscle contraction.
  • Adrenal glands: Secretes cholesterol, precursor for steroid hormones.
  • Liver: Synthesizes enzymes for detoxification (e.g., alcohol, drugs).

Conclusion

• The Endoplasmic Reticulum is crucial for cellular function and health.
• Further research may reveal additional functions.
• Encouragement to continue learning and engage with the content.