Chapter 10

Chapter 10: Multicellularity

10.2 Cell Junctions

• Cells produce an extracellular matrix for strength and support.

• Multicellular organisms utilize cell junctions to hold adjacent cells together.

• Cell junctions are primarily composed of proteins and serve various functions.

Types of Cell Junctions

Anchoring Junctions

• Function: Primarily hold adjacent cells together.

• Depend on integral proteins that pass through the cell membrane and connect to the cytoskeleton of neighboring cells.

• Key proteins involved: Cadherins and Integrins.

Cadherins

• Fibrous proteins linked to actin microfilaments in the cytoplasm.

• Extend into the extracellular matrix, where Ca2+ ions facilitate binding between them.

Integrins

• Made up of two subunits and bind to other proteins that attach to actin microfilaments.

• In the extracellular matrix, they connect to fibronectin, which ties to components like collagen fibers.

Tight Junctions

• Create seals between cells.

  • Limit movement of materials through intercellular spaces.

  • Restrict movement of proteins within the membrane.

Gap Junctions

• Composed of connexon proteins that form channels connecting the cytoplasm of adjacent cells.

• Function: Facilitate the passage of ions and small molecules for intercellular communication.

• Anchoring Junctions: Think of "A" for "Anchoring" and "Anchor" symbolizes strength and securing items together. You can remember the key proteins as Cadherins and Integrins: Cats Invite for security.

• Tight Junctions: Use the phrase "Tight Lid" to remember that they create seals and limit movement.

• Gap Junctions: Visualize a "Gap" or door that allows small items (ions and small molecules) to pass through, linking it to connectivity between neighbors.