Amoeboid movement is the most basic type of movement and perhaps the least understood. it refers to the characteristic crawling movement of some protists( Protozoa), Slime moulds and somewhat break cell such as white blood cells.
This crawling movement is also seen in the vertebrate kupffer cells in the liver ‚metastasizing cancerous cells, in animal cell in tissue culture, in the cells of the developing animal embryo and in any other cell where the movement is effected by p cytoplasmic streaming,Constant changes in the cell shape and extension of pseudopodia of. these changes can easily be seen under the microscope.
Amoeboid movement begins in a Cell or a single celled organisms like Amoeba by extension ‚of an arm like structure called the pseudo podium, In the required direction in to which the cytoplasm of a single cell or Single celled organisms flows.
the newly formed pseudo podium enlarge and the cell finally occupies the space where previously the news to the podiumpodium had begun to form.
There are two regions in the cytoplasm of the Amoeba under the light microscope which are as follows:
- i) The central Endoplasmic of granular plasma which is fluid in nature and is also called sole cytoplasm.
It contains granular inclusion and membranous particles that are in constant random motion
- ii) The peripheral clear gel like part of the cytoplasm called ectoplasm or hyaloplasm.
The ectoplasm contains three-dimensional network of actin and myosin filament (actin and myosin are found in all Eukaryotic cell)
The gel like region apparently decides the shape of the pseudo podium and may transmit tension from the reason of cellular contraction to the sides of contact with the substratum.
Locomotion in Amoeba is caused by continuous assembly and disassembly of the actin and myosin containing complexes.The ectoplasma at the front and becomes thin causing a pseudo podium to bulge forward.The rear end of the Amoeba contracts and pushes the streaming endoplasm into the elongating psedupodium .
In the region near the tip of pseudo podium the protein acting polymerises to form a filamentous network by the crosslinking of the actin protein and myosin protein.
The crosslinking of the actin protein and myosin protein cause the filamentous network to contract pulling the cell in the direction of the pseudo podium.
As a cell moves new pseudo podium forms in the direction of the movement, While the posterior part contract and are withdrawn. it is not known with certainty how the extension and retraction of the pseudo podium takes place.
It appears that there is a conversion of the cytoplasm from fluid like sol state to the semi solid gel state.
The energy required for locomotion comes from ATP. it is still not known how amoeboid movement is control or regulated. however it is known that Amoeba cannot extend their pseudopodia in all direction simultaneously if they could they would be ripped apart! It is known however that the ability of many actin binding protein to cross linked to actin is strongly dependent or calcium ion Concentration and ph.
Thus calcium and hydrogen ion and regulate the sol to gel transition.In low molar concentration of calcium ion and when pH is lowered to 6.8 the cytoplasm of the amoeba begins to set as a gel while solution of the gel starts when pH of calcium and is raised.
Study suggest that proteins such as gelsolin or villin are responsible for gel to SOL transition because these proteins fragment act in the presence of micromolar of free calcium ion.
It has been suggested that directed growth of pseudopodia is due to difference in calcium Ion or hydrogen ion concentration among various regions of the cytoplasm. whether this is the case however remains to be determined.