ch. 3

Cell Structure and Membrane Overview

• Cells: Smallest unit; types include prokaryotic and eukaryotic.
• Plasma Membrane Functions:
  • Physical isolation
  • Regulation of environmental exchange
  • Sensitivity to environment
  • Structural support

Fluid Mosaic Model

• Fluid Membrane: Contrasts with rigid plant cell wall; fluidity allows movement (e.g., amoeba movement).
• Components:
  • Lipids: Phospholipid bilayer with hydrophilic heads (polar) pointing out and hydrophobic tails (nonpolar) pointing inward.
  • Proteins: Various functions including channels and carriers.
  • Carbohydrates: Located on the exterior, aiding in recognition and protection.

Membrane Composition

• Phospholipids: Form bilayer in water; self-arranging properties.
• Cholesterol: Adds stability to the membrane structure.
• Proteins:
  • Integral/Transmembrane Proteins: Span the membrane, involved in transport.
  • Peripheral Proteins: Attach to the membrane surface; serve various functions.

Protein Functions in Membranes

• Transport Proteins: Carry substances across the membrane.
• Receptor Proteins: Bind signals for cellular response.
• Enzymes: Catalyze reactions.
• Recognition Proteins: Identify self vs. foreign cells (e.g., major histocompatibility proteins).
• Anchoring Proteins: Maintain tissue structure; important for cell adhesion.

Carbohydrates in Membranes

• Glycolipids and Glycoproteins: Integral roles in functionality; provide protection and recognition.
• Glycocalyx: Carbohydrate coating that protects cells; relevant in digestive systems, pathogen resistance.

Cell Junctions

• Tight Junctions: Create impermeable barriers between cells (e.g., in epidermis).
• Desmosomes: Provide strong adhesion between cells (mechanical strength).
• Gap Junctions: Allow communication between adjacent cells by providing channels for material exchange.

Conclusion

• Understanding membrane structure and functions is crucial for grasping cellular processes, including homeostasis and communication between cells.