Cell Membrane Structure and Function

Structure and Composition

• The cell membrane, also known as the plasma membrane, is a thin layer of lipid and protein molecules that surrounds the cell.
• It is semi-permeable, allowing certain substances to pass through while keeping others out.
• The cell membrane is composed of:
  • Phospholipid bilayer: a double layer of phospholipid molecules with hydrophilic (water-loving) heads and hydrophobic (water-fearing) tails.
  • Proteins: embedded or attached to the phospholipid bilayer, performing various functions such as transport, signaling, and cell adhesion.

Functions

• Regulation of what enters and leaves the cell: the cell membrane controls the movement of substances into and out of the cell through various transport mechanisms.
• Protection: the cell membrane acts as a barrier, protecting the cell from its environment and maintaining internal conditions.
• Cell signaling: the cell membrane plays a role in signal transduction, allowing cells to communicate with each other.
• Cell adhesion: the cell membrane helps cells stick together and maintain tissue structure.

Transport Mechanisms

• Passive transport: movement of substances down their concentration gradient, requiring no energy input from the cell.
  • Diffusion: random movement of particles from high to low concentration.
  • Osmosis: movement of water molecules from high to low concentration.
• Active transport: movement of substances against their concentration gradient, requiring energy input from the cell.
  • Carrier proteins: transport molecules across the cell membrane using energy from ATP.

Fluidity and Movement

• Fluid mosaic model: the cell membrane is a dynamic, fluid structure with proteins and lipids moving laterally.
• Lateral movement: proteins and lipids can move freely within the phospholipid bilayer.
• Flip-flop movement: phospholipid molecules can rotate from one side of the bilayer to the other.

Importance

• The cell membrane is essential for maintaining cellular homeostasis and regulating cellular activities.
• Its dysfunction can lead to various diseases and disorders, such as cancer and neurological disorders.