Cell Membrane Structure and Functions

Cell Membrane

Structure:

• Phospholipid bilayer: composed of two layers of phospholipid molecules with their hydrophilic (polar) heads facing outwards and hydrophobic (non-polar) tails facing inwards
• Embedded proteins: integral proteins (transmembrane) and peripheral proteins (attached to the surface)

Functions:

• Semipermeability: regulates the movement of substances in and out of the cell
• Protection: maintains cell shape and provides a barrier against external environment
• Cell signaling: proteins in the membrane can receive and transmit signals
• Cell recognition: unique proteins on the surface of the membrane allow cells to recognize each other

Properties:

• Fluidity: the ability of the membrane to change shape and move freely
• Permeability: the ability of substances to pass through the membrane
• Selectivity: the ability of the membrane to control what substances can pass through

Transport across the membrane:

• Passive transport: movement of substances down their concentration gradient without energy input (e.g. diffusion, osmosis)
• Active transport: movement of substances against their concentration gradient using energy input (e.g. carrier proteins, pumps)