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Cell Junctions and Intracellular Compartments

Unit 6: Intracellular Compartments

Objectives:

  • Identify types of cell junctions and how they work.
  • Identify the components of the cytoskeleton and what role each plays.
  • Identify how cells and organelles move.
  • Describe the role of the extracellular matrix.

Cell Junctions

  • Overview: Cell junctions are crucial for maintaining tissue integrity and allowing intercellular communication.
    • Tight Junctions:
    • Definition: An impermeable junction that encircles the cell.
    • Function: Prevents leakage of fluids between adjacent cells, creating a barrier.
    • Desmosomes:
    • Definition: Anchoring junctions that are scattered along the sides of cells.
    • Function: Provides mechanical stability by linking adjacent cells through protein interactions.
    • Gap Junctions:
    • Definition: A nexus that allows chemical substances to pass between cells.
    • Function: Facilitates intercellular communication and the sharing of ions and molecules.

Unit 7: Cytoskeleton and Cellular Movement

Cytoskeleton Overview

  • Definition: The cytoskeleton is a dynamic and elaborate series of rods running through the cytosol of the cell, providing structural support and shape.
  • Components:
    • Actin filaments (microfilaments):
    • Role: Involved in muscle contraction, cell division, and changes in cell shape.
    • Intermediate Filaments:
    • Role: Provides tensile strength and structural integrity to cells.
    • Microtubules:
    • Role: Functions as tracks for the movement of organelles and vesicles within the cell.

Movement of Cells and Organelles

  • Cells move through mechanisms such as:
    • Cytoplasmic streaming: Involved in the transport of materials within the cytoplasm.
    • Amoeboid movement: Enabled by actin polymerization and depolymerization.

Extracellular Matrix (ECM)

  • Role of Extracellular Matrix:
    • Provides structural and biochemical support to surrounding cells.
    • Composed of proteins and polysaccharides; helps anchor cells in place.
    • Important for tissue repair and regeneration.

Organelles in Detail

Golgi Apparatus

  • Role: Processes and packages proteins and other molecules for transport.
  • Structure: Consists of stacked membranes, critical to the sorting and distribution of proteins.

Lysosomes

  • Definition: Spherical membranous bags containing digestive enzymes.
  • Function:
    • Digests ingested bacteria, viruses, and toxins.
    • Degrades nonfunctional organelles and unneeded tissue.
    • Involved in breaking down glycogen and releasing thyroid hormone.
    • Capable of breaking down bone to release Calcium ($Ca^{2+}$).
  • Secretory lysosomes found in:
    • White blood cells
    • Immune cells
    • Melanocytes

Peroxisomes

  • Definition: Membranous sacs containing oxidases and catalases.
  • Function: Detoxifies harmful or toxic substances, such as hydrogen peroxide ($H2O2$) and neutralizes dangerous free radicals.
  • Alternative names: Detoxifying organelles, as they neutralize highly reactive chemicals with unpaired electrons (e.g., superoxide ion $O_2^-$).

Cell Adhesion Molecules (CAMs)

  • Definition: CAMs are proteins that anchor cells to the extracellular matrix.
  • Functions:
    • Assist in the movement of cells past one another.
    • Mobilize protective white blood cells to areas of injury or infection.

Adherens Junctions

  • Specific type of junction connecting cells through cadherin proteins, contributing to the strength and stability of tissues.
  • Also known as Zonula adherens; key role in maintaining tissue architecture.

Conclusion

  • The intracellular components facilitate various cell functions including metabolism, communication, and structural integrity. Understanding their roles enables insights into the complexities of cellular interactions and the overall functionality of living organisms.