Membrane proteins include embedded and surface-associated proteins that transport substances, receive signals, catalyse reactions, and support adhesion; Their positions explain how one membrane can perform many different cellular functions.
Coverage 2017–2023 · Updated 15 Jul 2026
Integral proteins are embedded in one or both lipid layers and may span the membrane; peripheral proteins attach to one surface or to another membrane protein.
Hydrophobic amino-acid regions of integral proteins interact with lipid tails, while hydrophilic regions face water or form pores. Peripheral proteins remain surface-associated and can detach without crossing the hydrophobic core.
| Location | Typical functions |
|---|---|
| Integral | Channels, carriers, pumps, receptors, enzymes and cell-recognition proteins |
| Peripheral | Cytoskeletal anchors, scaffolds, enzymes and signalling partners on a membrane surface |
A channel spanning the bilayer is integral, while a cytoskeletal protein attached to its cytoplasmic face is peripheral.
Function alone does not determine the category. Classify a protein by whether it enters the hydrophobic bilayer core or remains surface-associated.
This objective is assessed through structured response, commonly using State / Identify / Outline.
State / Identify / Outline / Describe / Explain / Label
Build the answer around this relationship: Integral proteins are embedded in the bilayer and may span it completely.
Listing non-membrane processes such as DNA replication or glycolysis as membrane protein functions.
Representative question
Describe the functions of proteins in cell membranes.
The SL membrane model is a decision system. The bilayer forms because phospholipids are amphipathic, and the hydrophobic core creates selective permeability. Small non-polar molecules diffuse directly; water moves by osmosis and often through aquaporins; ions and polar molecules use channels or transporters; pumps use ATP for movement against gradients. Proteins and glycocalyx components add transport, recognition, and model evidence.
