Re: paramecium

Actually, the enzymatic motors that are used to move cilia are very similar to the enzymatic motors used to make muscles contract. In both cases, a group of very long, rigid protein molecules are moved relative to each other by enzymes called Motor proteins. Motor proteins are specialized enzymes that attach to long filaments in the cell and crawl along these filaments using ATP as an energy source. There are three main groups of motor proteins: Myosins, Dyneins, and Kinesins . Myosins are the motors used in muscles, and they move on microfilaments made out of a protein called actin (actin and myosin make up the majority of the protein found in meat, although both are found in every cell in the body). Dyneins and Kinesins move along hollow filaments called microtubules made out of a protein called tubulin, but they move in opposite directions along the outside of the tube, which requires different types of motors. Paramecia have actin microfilaments and microtubules along with all three types of motor proteins, but only one set is responsible for moving the cilia.

Cilia are composed of special arrays of microtubules called axonemes with 9 double tubes around 2 single tubes. Looking like bridges between the sets of double tubes are dyneins which are anchored to one double tube and move along its neighbor. When activated, the dyneins try to slide the tubules by each other, causing the whole axoneme to twist and bend. The dyneins only slide the tubules so far before other proteins called Nexins act like rubber bands and pull the tubules back to their original places. By alternating between bending and releasing the axoneme, the cilium develops a beating motion which propels the cell. So Paramecia move their cilia in much the same way that we move our muscles - by using motor proteins to move long filaments past each other.