Lecture 2C

The Golgi Apparatus: Functions and Structure

  • Overview of the Golgi Apparatus

    • The Golgi apparatus is crucial as the shipping and receiving center of the eukaryotic cell.

    • Part of the endomembrane system of a cell.

Functions of the Golgi Apparatus

  • Modifications

    • Modifies products synthesized in the endoplasmic reticulum (ER).

  • Manufacturing

    • Manufactures certain macromolecules (e.g., polysaccharides).

  • Sorting and Packaging

    • Sorts and packages materials into transport vesicles for various destinations.

Structure of the Golgi Apparatus

  • Composed of flattened membranous sacs known as cisternae.

  • Structural views include:

    • Sectional view of Golgi body from the stem of the horsetail Equisetum hyemale.

    • Surface view of a single cisterna.

  • Faces of the Golgi Apparatus:

    • Cis face (receiving side): This is where vesicles from the ER fuse with the Golgi apparatus.

    • Trans face (shipping side): Vesicles bud off from this side and transport proteins to other locations.

Vesicle Movement and Functionality

  • Vesicular Transport

    • Vesicles move from the ER to the Golgi apparatus containing specific proteins.

    • Vesicles also transport certain proteins back to the ER as needed.

  • Cisternal Maturation Process

    • Golgi cisternae undergo changes in composition and function as they move from the cis face to the trans face.

    • New vesicles form and leave the Golgi, carrying proteins or materials to the plasma membrane for secretion.

Vesicular Components Related to Golgi Apparatus

  • Types of Vesicles:

    • Shuttle vesicles: Involved in the transitional processes between the ER and Golgi.

    • Secretory vesicles: Contain materials destined for secretion out of the cell.

  • Transportation pathways include:

    1. Transport vesicles from nucleus through nuclear pores.

    2. Movement from the rough endoplasmic reticulum to the Golgi and beyond.

Lysosomes: Digestive Compartments within the Cell

  • Definition of Lysosome: A lysosome is a membranous sac of hydrolytic enzymes that can digest macromolecules.

  • Enzymatic Functions:

    • Capable of hydrolyzing proteins, fats, polysaccharides, and nucleic acids.

    • Participates in recycling cellular materials through a process called autophagy.

Processes Associated with Lysosomes

  • Phagocytosis:

    • A cellular mechanism where the plasma membrane engulfs a large particle (≥ 0.5 μm), forming a compartment called a phagosome, which then fuses with a lysosome for digestion.

    • Outcomes include the breakdown of food particles using hydrolytic enzymes that the lysosome contains.

  • Autophagy:

    • This is the process governed by the lysosome for degrading unnecessary or dysfunctional cellular components in a regulated manner.

    • Facilitates the recycling of organelles and cellular materials.

Vesicles: Structural and Functional Insights

  • Vesicle Definition: A vesicle is a structure within or outside a cell consisting of liquid or cytoplasm enclosed by a membrane layer.

  • Roles of Vesicles:

    • Essential for organizing cellular substances and engaging in transactions such as secretion (exocytosis) and material uptake (endocytosis).

Overview of the Endomembrane System

  • The endomembrane system consists of interconnected and dynamic structures essential for the organization of cellular compartments, including:

    • Nuclear envelope

    • Nucleus

    • Rough and smooth endoplasmic reticulum (ER)

    • Transport vesicles

    • Cis and trans Golgi

    • Plasma membrane

  • The entire endomembrane system is involved in the regulation and distribution of materials throughout the cell, ensuring cellular homeostasis and functionality.