Tangles destroy a vital cell transport system made of proteins. This electron microscope picture shows a cell with some healthy areas and other areas where tangles are forming.
In healthy areas:
The transport system is organized in orderly parallel strands somewhat like railroad tracks. Food molecules, cell parts and other key materials travel along the "tracks."
A protein called tau (rhymes with wow) helps the tracks stay straight.
In areas where tangles are forming:
Tau collapses into twisted strands called tangles.
The tracks can no longer stay straight. They fall apart and disintegrate.
Nutrients and other essential supplies can no longer move through the cells, which eventually die.