A structural arrangement of 6-12 transmembrane domains is common among mammalian proteins that transport small organic molecules.

The "machinery" is a group of special molecules designed to transport large molecules across the cell membrane.

Thus they may only transport molecules with the solute gradient, and not against it.

Cells in a sugar source "load" a sieve-tube element by actively transporting solute molecules into it.

The tight junctions have a net negative charge, and are believed to preferentially transport positively-charged molecules.

Coat-proteins, like clathrin, are used to build small vesicles in order to safely transport molecules within and between cells.

The gradient can be used to transport molecules across membranes.

Ordinarily, bile serves as a carrier that transports fat molecules into the bloodstream.

They also provide evidence, in culture, for a novel mechanism used by cell protrusions to transport molecules and organelles.

Drawbacks to transporting larger molecules is a reduction in the maximum energy, or depth, that the molecule can be implanted.