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Overview of Golgi Apparatus Functions

May 2, 2025

Notes on Golgi Apparatus Lecture

Introduction

  • Discussion on the Golgi apparatus and its structure.

Structure of Golgi Apparatus

  • Composed of flattened sacs known as cisternae.
  • Cisternae in Golgi apparatus are not physically connected.

Functions of the Golgi Apparatus

  1. Receiving Products: Accepts products from the endoplasmic reticulum (ER).
  2. Sorting: Organizes products into different categories.
  3. Tagging: Tags products for transportation (similar to addressing a package).
  4. Transportation: Dispatches products to their destination (organelle or plasma membrane).

Directionality of Golgi Apparatus

  • Two phases:
    • Cis end: Receiving side.
    • Trans end: Shipping side.
  • Movement is from cis to trans end.
  • Vesicles can sometimes move backward to earlier cisternae or the ER.

Models of Transport in Golgi Apparatus

1. Vesicular Transport Model

  • Proteins move in vesicles from one cisterna to the next.
  • Vesicles bud off from the cis network and transport proteins through the Golgi.
  • Some proteins may be sent back if improperly matured.

2. Cisternal Maturation Model

  • Instead of vesicles, entire clusters of cisternae move through the Golgi.
  • Proteins mature as cisternae progress from cis to trans phase.
  • Backward movement of proteins still occurs in vesicles.

Movement of Vesicles Between ER and Golgi Apparatus

  • Forward Movement (Anterograde):
    • Vesicles bud off from the ER and fuse with the Golgi.
    • Coated with COPII proteins during transport.
  • Backward Movement (Retrograde):
    • Mis-sorted or needed proteins are sent back to the ER.
    • Coated with COPI proteins.

SNARE Proteins in Vesicle Fusion

  • V-SNARE: Located on vesicle membrane.
  • T-SNARE: Located on target membrane (Golgi or ER).
  • SNAREs facilitate docking and fusion of vesicles to target membranes.

Role of Rab Proteins

  • Rab GTPases assist in vesicle docking to target membranes.
  • Tethering occurs between Rab GTPases and effector proteins on the target membrane.

Types of Coat Proteins

  1. COPII: For anterograde movement from ER to Golgi.
  2. COPI: For retrograde movement from Golgi to ER.
  3. Clathrin: Used for transport from trans Golgi to plasma membrane or endosomes (also involved in endocytosis).

Conclusion

  • Understanding vesicular trafficking is essential for cell function.
  • Questions are welcomed for further clarification.

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