BSC1010C: General Biology 1 - Cell Structure (Module 4, Part 3)

Introduction to Cell Structure and Interaction

  • Course: BSC1010C: General Biology 1
  • Topic: Cell Structure (Chapter 4 B2E)
  • Module: 4 - Part 3

Learning Objectives

  • Describe the extracellular matrix (ECM).
  • List examples of how plant and animal cells communicate with adjacent cells.
  • Summarize the roles of:
    • Tight junctions
    • Desmosomes
    • Gap junctions
    • Plasmodesmata

Cell Surface Exploration & Interaction

Cells modify their environment and interact through various structures and mechanisms. These interactions are crucial for tissue formation, communication, and maintaining cellular integrity.

1. Extracellular Matrix (ECM)
  • Definition: A complex network of macromolecules secreted by cells that provides structural and biochemical support to the surrounding cells.
  • Composition (in animal cells): Primarily made of:
    • Collagen fibers: Provide strength and resist stretching.
    • Proteoglycans: Form a gel-like substance that resists compression and hydrates the ECM.
    • Fibronectin: Connects cells to the ECM.
    • Laminin: A glycoprotein found in the basal lamina, key for cell adhesion and differentiation.
  • Functions:
    • Provides structural support and anchorage for cells.
    • Involved in cell adhesion, migration, proliferation, and differentiation.
    • Plays a role in tissue development, repair, and signaling.
2. Cell Communication with Adjacent Cells

Cells communicate directly through specialized junctions.

2.1. Animal Cell Junctions
  • Tight Junctions (Occluding Junctions)
    • Role: Form a watertight seal between adjacent animal cells, preventing the passage of substances through the extracellular space between the cells.
    • Location: Common in epithelial tissues (e.g., lining of intestines, bladder) where they regulate permeability.
    • Structure: Composed of proteins like claudins and occludins that fuse cell membranes.
  • Desmosomes (Anchoring Junctions)
    • Role: Act as "spot welds," providing strong adhesion between adjacent animal cells, giving tissues mechanical strength.
    • Location: Abundant in tissues that experience mechanical stress (e.g., skin, heart muscle).
    • Structure: Linked to intermediate filaments (e.g., keratin) within the cytoskeleton, providing a strong connection.
  • Gap Junctions (Communicating Junctions)
    • Role: Create channels between adjacent animal cells, allowing for direct exchange of small molecules (ions, sugars, amino acids, signaling molecules) and electrical signals.
    • Location: Found in many tissues, important for coordinated activity (e.g., heart muscle contraction, nerve signal transmission).
    • Structure: Formed by protein complexes called connexons, each made of six connexin proteins.
2.2. Plant Cell Junctions
  • Plasmodesmata
    • Role: Channels that pass through the cell walls of adjacent plant cells, connecting their cytoplasm and endoplasmic reticula.
    • Function: Allow direct intercellular communication and transport of water, nutrients, signaling molecules, and even small proteins and RNA between plant cells.
    • Structure: Lined by the plasma membrane and contain a desmotubule (a modified ER tubule).