Cell Membrane Structure and Functions

Cell Membrane Structure

• The cell membrane, also known as the plasma membrane, is a selectively permeable barrier surrounding all cells.
• It's a fluid mosaic model, primarily composed of phospholipids arranged in a bilayer.
• Embedded within the phospholipid bilayer are various proteins: integral proteins spanning the membrane and peripheral proteins loosely bound.
• Cholesterol contributes to membrane fluidity and stability.
• Carbohydrates are attached to proteins (glycoproteins) and lipids (glycolipids), crucial for cell recognition and communication.
• Hydrophobic tails of phospholipids face each other, and hydrophilic heads face the aqueous environments inside and outside the cell.

Membrane Functions

• Regulates substance passage into and out of the cell.
• Provides a surface for biochemical reactions.
• Maintains cell shape and integrity.
• Enables cell-to-cell communication.

Types of Cell Transport

• Passive transport doesn't require cellular energy.
  • Diffusion moves molecules from high to low concentration until equilibrium. Factors include concentration gradient, temperature, and molecule size.
  • Facilitated diffusion uses transport proteins to aid specific molecule movement down their concentration gradient. Includes channel proteins (e.g., ion channels) and carrier proteins.
  • Osmosis is water diffusion across a selectively permeable membrane, from high to low water concentration, crucial for maintaining cell volume and pressure.
• Active transport requires cellular energy, typically ATP.
  • Sodium-potassium pump actively maintains sodium and potassium ion gradients across the membrane.
  • Endocytosis brings material into the cell by membrane infolding. Includes phagocytosis (engulfing large particles) and pinocytosis (engulfing fluids).
  • Exocytosis releases material from the cell via vesicle fusion with the membrane. Essential for protein and hormone secretion.

Factors Affecting Cell Transport

• Size of molecules affects diffusion rate; smaller molecules diffuse faster.
• Concentration gradient influences transport speed; larger gradients mean faster transport.
• Temperature generally increases transport rates.
• Surface area of the membrane increases transport rates (like diffusion).
• Membrane thickness affects diffusion speed; thinner membranes facilitate faster diffusion.
• Membrane proteins significantly enhance facilitated diffusion and active transport rates.

Importance of Cell Transport

• Nutrient uptake provides essential nutrients for energy and growth.
• Waste elimination removes waste products for homeostasis.
• Signal transduction allows cell communication via signaling molecules.
• Homeostasis maintenance results from appropriate component influx/efflux.

Specific Examples of Transport

• Glucose transport often uses facilitated diffusion via carrier proteins.
• Ion movement is crucial for nerve impulses and muscle contractions; often employs passive or active transport along ion gradients.
• Hormone secretion typically involves exocytosis.
• Immune response includes phagocytosis for pathogen and foreign material engulfment.

This quiz explores the structure and functions of the cell membrane, also known as the plasma membrane. Participants will learn about its composition, including the fluid mosaic model, and the roles of various molecules like proteins, cholesterol, and carbohydrates. Understand how the cell membrane regulates substance passage and facilitates communication.