Basic membrane structure
Fluid-mosaic model: a model describing the arrangement and movement of phospholipids, proteins, glycoproteins and glycolipids within a cell membrane.
Cell-surface membranes and the membranes surrounding eukaryotic organelles share the same basic organisation. This applies to membranes associated with structures including the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, chloroplasts and lysosomes. Each is based on a phospholipid bilayer containing proteins and other membrane components.
The resulting membrane is flexible and partially permeable. It controls exchange between compartments and also has roles in signalling, cell recognition and communication.
Main components
- Phospholipid bilayer
- Intrinsic and extrinsic proteins
- Glycoproteins and glycolipids
- Cholesterol may be present
Why is it called fluid mosaic?
Fluid
Phospholipids and some proteins can move sideways within the bilayer. Because these components are not fixed in one position, the membrane remains flexible.
Mosaic
Different membrane proteins occur at different positions among the phospholipids, creating the varied arrangement described as a mosaic.
Exam Tip: When explaining the name fluid mosaic, give both parts: relate fluid to sideways movement of phospholipids and some proteins, then relate mosaic to the varied arrangement of proteins within the bilayer. A labelled drawing should clearly identify the phospholipid bilayer and its main components.