How do human/animal cells move?
1 Answer
It depends upon the cell, but the general method employed by animal cells (including human cells) is re-arranging special filaments inside the cell.
Inside animal cells, you find a special type of "scaffolding", like an interior skeleton. This is called the cytoskeleton . This cytoskeleton is very dynamic: it constantly changes in response to stimuli.
Cell movement can happen when actin filaments (one of the 3 types of filament which makes up the cytoskeleton) rapidly change shape. For example, when a cell needs to move towards a chemical (such as a chemical released by a pathogen), that chemical of interest will bind to receptors on the cell membrane and trigger the actin filaments inside the cell to form a "mesh" at the leading edge of the cell. This basically pushes the leading edge of the cell towards the chemical of interest. Check out the YouTube Video I attached to this answer: it shows a white blood cell chasing a pathogen using this method! Cool, huh?
Other things happen too, thanks to the cytoskeleton: for example, the leading edge (after being pushed by the actin filaments in response to some kind of stimulus) "grips" onto the surface of whatever the cell is moving across (e.g. the extra-cellular matrix, the stuff which exists outside cells in your body, or the surface of a microscope slide). Then, special protein motors contract the cytoskeleton filaments (in a similar way to how your muscles work!) so that the cell is "pulled" in the correct direction.
But don't forget, there are other ways that cells can move too. Think of a sperm cell: it has a flagellum , a special "tail" made of microtubules which can "whip" to propel the cell forwards.
Whilst not eucaryotes, I recently did some research into bacteria which used a special protrusion called a pilus to "drag themselves" along surfaces, a bit like using a grappling hook. These structures actually acted as receptors for viruses, and so whenever there were too many harmful viruses around, the bacterial populations evolved resistance by losing their pilus: so they couldn't drag themselves around anymore!
Hope this helps.
Ben
