2 Neuroscience2.5 Neurochemistry and neurophysiology
2.5.2.6 Endocytosis and vesicle recycling
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Written by Resident Doctor Committee · Published
New in the 2027 syllabus
The College added this topic for exams from January 2027.
Bringing membrane and cargo into cells
In endocytosis, the cell takes in a patch of its surface membrane, along with material from outside, inside a vesicle. This lets it take up large molecules and pull receptors back from the surface.
Receptor-mediated endocytosis is the selective form. Receptors, adaptor proteins and other machinery at the membrane work together to gather chosen cargo.
Early endosomes sort what comes in. Some goes to recycling pathways. The rest moves on to later endosomes and lysosomes to be broken down.
Receptor internalisation can make the cell less responsive at its surface. It can also let receptors be recycled, or let signalling carry on inside the cell.
Recycling at synapses
Stage | What happens |
|---|---|
Membrane retrieval | Takes back the membrane added by exocytosis, keeping the surface in balance |
Membrane fission | Dynamin helps pinch the endocytic structure off the surface |
Sorting and vesicle reformation | Gathers synaptic vesicle proteins back into usable vesicles |
Acidification | A proton pump rebuilds the gradient across the vesicle membrane |
Transmitter loading | Vesicular transporters use that gradient to refill the vesicle |
Clathrin-dependent pathways build a protein coat that forms the vesicle. Synapses also retrieve membrane by faster routes that do not need clathrin.
Activity and temperature affect which route dominates. No single fixed sequence describes every synapse or every experimental condition.
Endocytosis is not reuptake. Endocytosis retrieves membrane and cargo. Reuptake transporters move transmitter molecules across a membrane that is already there.
If recycling fails, releasable vesicles run out during sustained activity, even when the neuron can still make transmitter normally.