Cell
Motil
ity
Howard Stebbings,
University of Exeter, Exeter,
UK
Movement is a major characteristic of living organisms,
and can take the form either of movements of cells or of
movements within cells themselves.
Introduction
Movement is a major
characteristic of living
organisms, and can take the
form either of movements of
cells or of movements within
cells themselves. Lower
prokaryotic cells, such as some
bacteria, are able to swim
within their environment with
the aid of fine appendages, but
the motile
Introductory article
Article Contents
•Introduction
•Swimming Cells: Bacteria, Ciliates and Flagellates, Sperm
•Crawling Cells: Amoebae, Leucocytes
•Internal Movements: Cytoplasmic Streaming, Vesicle Transport
•Dividing Cells, Contracting Cells
•Movements in Tissues: Fibroblasts, Growth Cones, Cancer Cells
•Cell Movements in Development
repertoire exhibited by higher eukaryotic cells
is much greater. Higher cells may also have
beating appendages in the form of numerous
short cilia or fewer longer flagella, and in
unicellular protozoa these function in a
coordinated way, not only to propel the
organism but also to assist feeding. Cilia are
also present on cells of certain
differentiated tissues of metazoans, where their
beating serves to move the environment
relative to the stationary cells. Not all protozoa
move by means of cilia and flagella. Some, such
as freshwater and soil amoebae, crawl over
their substrates, and a variety of cells, such as
leucocytes, in multicellular organisms show
similar crawling movements. Higher cells, as
well as being much larger than bacteria, have
separate nuclear and cytoplasmic
compartments and often show considerable
asymmetry. This has necessitated the
development of mechanisms for moving
components intracellularly, a property that is
well illustrated by plant cells, many of which
show different forms of exaggerated
cytoplasmic streaming. Intracellular movement
is also an important feature of animal cells
in which organelles, vesicles and genetic
messages are transported to and from specific
sites within the cell. Replicated genetic material
within chromosomes is also separated into two
prospective
daughter cells by similar mechanisms.
Many cells are capable of shape changes as
a result of reversible or irreversible contraction.
The most obvious examples of cellular
contraction are seen in muscle tissue. Similar
contractions, however, also occur in cells of
other tissues, and the division of a cell’s
cytoplasm following the separation of its
genetic material at mitosis is the result of a
drawstring-like contraction.
A further type of movement is typified by
fibroblasts, cells of mesodermal origin, which
migrate individually through connective tissue
and synthesize collagen in the extracellular
matrix. Their movement differs from that of
amoebae in that they do not show continual
deformation during migration, but glide over
their substrate as a result of extension,
attachment and contraction of a broad,
flattened, leading edge. Indeed, in a similar
fashion the growth cone at the tip of axons of
differentiating nerve cells
