The body's cells crawl from one place to another by rearranging their internal skeleton, scientists say.
Cells move around by means of a "push and pull" mechanism
The finding could advance understanding of how tumours move around and how the immune system works.
The UK Medical Research Council study, published in the journal Science, looked at the sperm cells of parasitic worms.
It showed a "push and pull" mechanism where thin strands of material at the front of a cell push out while the opposite happens at the back.
It was already known that cells move by pushing out their front ends while at the same time pulling in their rear, but how this works at a molecular level has been unclear until now.
The scientists described how the cell movement is based on the way parts of the cellular internal skeleton group together and then separate.
Surprisingly, the "push and pull" mechanism did not appear to use some proteins previously thought essential for cell movement.
Lead scientist Dr Murray Stewart, from the MRC's Laboratory of Molecular Biology, said: "Although the mechanism these cells use is a very simple one, it shows that cell movement need not be as complex as many scientists have imagined and brings closer the possibility of using this knowledge to develop new strategies to enhance the treatment of injury and disease."