Topic 4) Cell Membranes and Transport (AS)

Fluid Mosaic Model

Describes the structure of cell membranes as a dynamic and flexible arrangement of phospholipids and proteins.

Phospholipid Bilayer

Composed of two layers of phospholipids with hydrophilic heads facing outward and hydrophobic tails facing inward.

Integral Proteins

Proteins that span the entire membrane and are involved in transport, acting as channels or carriers.

Peripheral Proteins

Proteins attached to the inner or outer surface of the membrane that play roles in signaling and cell recognition.

Cholesterol

Molecules mixed among phospholipids that stabilize membrane fluidity, preventing excessive movement or rigidity.

Glycoproteins

Carbohydrate chains attached to proteins on the extracellular surface involved in cell recognition and signaling.

Glycolipids

Carbohydrate chains attached to lipids on the extracellular surface, playing roles in immune responses and tissue structure.

Passive Transport

Movement of substances across the membrane without energy expenditure, occurring down a concentration gradient.

Diffusion

Net movement of molecules from an area of higher concentration to an area of lower concentration through the phospholipid bilayer.

Facilitated Diffusion

Utilizes transport proteins to move larger or polar molecules across the membrane.

Osmosis

Specific type of facilitated diffusion involving the movement of water molecules through aquaporins.

Active Transport

Movement of substances against their concentration gradient requiring energy in the form of ATP.

Sodium-Potassium Pump

A carrier protein that transports sodium out of the cell and potassium into the cell.

Bulk Transport

Movement of large quantities of substances into or out of the cell via vesicles, requiring energy.

Endocytosis

Process by which cells engulf external substances, including phagocytosis and pinocytosis.

Exocytosis

Process by which cells expel substances, fusing vesicles with the plasma membrane.