Amoeboid movement

Amoeboid movement is the most typical mode of locomotion in adherent eukaryotic cells. It is a crawling-like type of movement accomplished by protrusion of cytoplasm of the cell involving the formation of pseudopodia ("false-feet") and posterior uropods. One or more pseudopodia may be produced at a time depending on the organism, but all amoeboid movement is characterized by the movement of organisms with an amorphous form that possess no set motility structures. Movement occurs when the cytoplasm slides and forms a pseudopodium in front to pull the cell forward. Some examples of organisms that exhibit this type of locomotion are amoebae (such as Amoeba proteus and Naegleria gruberi,) and slime molds, as well as some cells in humans such as leukocytes. Sarcomas, or cancers arising from connective tissue cells, are particularly adept at amoeboid movement, thus leading to their high rate of metastasis. This type of movement has been linked to changes in action potential. While several hypotheses have been proposed to explain the mechanism of amoeboid movement, its exact mechanisms are not yet well understood. Assembly and disassembly of actin filaments in cells may be important to the biochemical and biophysical mechanisms that contribute to different types of cellular movements in both striated muscle structures and nonmuscle cells. Polarity gives cells distinct leading and lagging edges through the shifting of proteins selectively to the poles, and may play an important role in eukaryotic chemotaxis. Crawling is one form of amoeboid movement which starts when an extension of the moving cell (pseudopod) binds tightly to the surface. The main bulk of the cell pulls itself toward the bound patch. By repeating this process the cell can move until the first bound patch is at the very end of the cell, at which point it detaches. The speed at which cells crawl can vary greatly, but generally crawling is faster than swimming, but slower than gliding on a smooth surface.