Inside the cell
How do things get around in the cell?
The inside of the cell is a scene of constant motion. Soluble molecules move around apparently randomly in the cytoplasm (because of random Brownian motion), but other components are transported more precisely. Many proteins are only allowed into one of the cellular compartments. Cells also have an elaborate network of fine protein filaments (strands), an interior cytoskeleton, which helps them keep their shape and provides the rails of a transport system.
Small protein motors pull vesicles, full of cell products, up or down microtubules or actin filaments. Special labels ensure the right cargo is sent to the right destination. These are usually proteins, or parts of proteins, sticking out of the vesicle.
The same system also moves organelles around or anchors them in place. The cell uses a lot of energy for all this transport, but it needs to speed things along. A protein molecule might take years to travel the length of the longest neuron (or nerve cells) (the sciatic nerve in your leg) by simple diffusion, but if it is bagged up and dragged along a microtubule it can cover 10 cm in a day. This is vastly more than most distances within cells, and means that even the ends of the long, drawn-out extensions of nerve cells, the axons, in your fingers or toes can be reached in a few days.