The lamellipodia formed are branched networks of actin filaments that stretch out from the cell. Filopodia are similar but they have the ability to sense the physical and chemical characteristics of the environment. In order to move, the cell needs to adhere to a point in the matrix. These focal adhesions connect to actin in the cytoskeleton after ligands in the extracellular matrix bind to integrins, which are receptors on the cell surface. This causes the adhesions to occur, which provide traction for the cell. They also sense the environment for the rest of the cell. Actin and myosin at the leading edge will provide the contractile force that causes the cell to move. These adhesions need to disassemble in order to allow the cell to move. There are kinases and phosphatases that help these adhesions turn over as the cell progresses. It is particularly important to have the rear end of the cell to disassemble the adhesions so that the cell can move forward.
MICROTUBULES As mentioned, microtubules are hollow and made from alpha tubulin and beta tubulin proteins. They are important in giving the organelles their proper location. Figure 58 shows the structure of the microtubule:
Figure 58.
184
