Cytoskeletal Motility

Albrecht-Buehler (1985):

Cell movement ... appears to be determined by some kind of chemical computer, the nature of which is beyond our present understanding.

Cell motility was discovered by van Leeuwenhoek who observed flagella propelled sperm cells swimming in the 17th century. A variety of cytoplasmic movements include "amoeboid" creeping over a surface, internal streaming, axoplasmic transport, muscle contraction, ciliary and flagellar bending, and cell shape changes. These maneuverings are all engineered by a relatively small group of proteins whose net collective effects can be quite spectacular. For example, lymphocytes and macrophages are white blood cells which combat infection by migrating from the blood stream into an open wound to engulf invading bacteria or foreign material. Cells of developing embryos perform precisely choreographed movements that give rise to different tissues. Internal movement such as the streaming of cytoplasm, secretion of cell product vesicles (i.e. neurotransmitters), engulfment of matter, and the separation of paired chromosomes in cell division are routine functions whose complexity, organization, and precision generally boggle biologists.

Also, well controlled muscle contraction which depends on the conformational bending of myosin head molecules can result in strenuously running a 4 minute mile, or delicately painting a Mona Lisa. Four categories of cytoplasmic movement and force generation will be considered with attention to their regulatory mechanisms. These are: cytoplasmic probing, bending sidearms, ciliary and collective movements, and geodesic tensegrity structures.

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