B2.1 Membrane & membrane transport

Phospholipid bilayer

The basic structural unit of cell membranes formed by two layers of phospholipids.

Amphipathic

Describes molecules that have both hydrophilic (water-attracting) and hydrophobic (water-repelling) regions.

Hydrophilic head

The polar part of a phospholipid that is attracted to water, typically containing a phosphate group.

Hydrophobic tail

The non-polar part of a phospholipid made of fatty acid chains that repels water.

Fluid mosaic model

A model describing the structure of cell membranes as a mosaic of diverse protein molecules embedded in a fluid phospholipid bilayer.

Integral proteins

Membrane proteins that are embedded in the phospholipid bilayer and can extend across one or both layers.

Peripheral proteins

Membrane proteins that are attached to the surface of integral proteins or the plasma membrane.

Facilitated diffusion

Process by which polar and charged molecules pass through a membrane via specific channels without the use of energy.

Active transport

The movement of substances across a membrane against their concentration gradient, requiring energy from ATP.

Aquaporins

Integral protein channels in membranes that facilitate the rapid transport of water molecules.

Glycoproteins

Membrane proteins that have carbohydrate chains attached, playing a key role in cell recognition.

Glycolipids

Lipids with carbohydrate chains attached on the extracellular side, important for cell recognition.

Simple diffusion

The passive movement of particles from an area of higher concentration to lower concentration through the membrane.

Selectively permeable

A property of cell membranes that allows them to control what enters and leaves the cell.

Channel proteins

Membrane proteins that form pores, allowing specific ions or molecules to cross the membrane.

Carrier proteins

Membrane proteins that transport substances across the membrane by changing shape, used in active transport.