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Multicellularity

• Advantages of multicellularity: coordination, growth, specialized functions.

• Costs: greater complexity, resource allocation, coordination of cells.

Extracellular Matrix (ECM)

• Definition: A framework of proteins and polysaccharides providing structural support.

• Functions: strength, structural support, organization, cell signaling.

• ECM components: polysaccharides, fibrous proteins (collagen, elastin).

Cells and ECM Interaction

• Adhesive proteins: cross-link ECM molecules and assist cell attachment (e.g., fibronectin, laminin).

• Structural proteins: provide strength and elasticity (collagen, elastin); proteins synthesized in the cytoplasm, processed in ER and Golgi before secretion.

Collagen

• Major component of bones, cartilage, tendons, and skin; makes up 25% of protein mass.

• Types of collagen:

  • Type I: strong, found in tendons and ligaments.

  • Type II: flexible, found in cartilage.

  • Type IV: forms filtration sheets in kidneys, skin, intestines.

Elastin

• Key feature of aorta, provides elasticity and strength; stretches and recoils.

Polysaccharides in ECM

• Proteoglycans: protein core with sugars that attract water, creating a gel-like texture.

Plant Cell Walls

• Components: cellulose (structural polysaccharide) and lignin (provides rigidity).

• Cellulose forms microfibrils, contributing to cell wall strength.

Cell Junctions

• Animal cell junctions: anchoring (cadherins), tight (prevent leakage), gap (allow molecule exchange).

• Plant cell junctions: middle lamella (adhering walls), plasmodesmata (small molecule exchange).

Cell Adhesion Molecules (CAMs)

• Cadherins: calcium-dependent, link cells together.

• Integrins: bind cells to ECM, facilitating communication and signaling.