Kinesin and Myosin are motor proteins. Motor proteins are molecular motors that move on the surface of a suitable substrate. The image can be likened to a train moving over a railway track except that Kinesin and Myosin are two different trains requiring two different types of tracks. The movement of these motor molecules is powered by the breakdown of the universal energy molecule called as ATP – Adenosine tri phosphate.  Both Kinesin and myosin are responsible for active transport of cell nutrients (carbohydrates, proteins, fats), membrane bound organelles and vesicles within the cellular cytoplasm. High resolution electron microscopy has helped to identify certain structural and functional differences between Kinesin and Myosin. The molecules are seen to differ in binding site, ATPase sites and cargo binding sites.

Kinesin motor protein:

Kinesin is the most common motor protein found in all vertebrates. It occurs in both neuronal and non-neuronal cells. It is a thin rod shaped protein around 80nm in length, with two globular heads connected to a fan like tail by a long stalk. The Kinesin motor molecule moves along microtubules by interacting with the tubular protein. It moves towards the plus end of the microtubule that is away from the centre and towards the periphery of the cell. So we can say that Kinesin carries cargo towards the cell periphery. Kinesin is responsible for fast axonal transport, formation of spindle apparatus and separation of chromosomes during mitosis and meiosis and transport of membrane bound organelles. It is also involved in constituting the membrane that lies between the Golgi complex and endoplasmic reticulum.  But it does not constitute the membranes of these two organelles. Kinesin deficiency can cause Charcot Marie tooth syndrome and kidney diseases.

Myosin Motor protein:

Myosin is a motor protein that is found in muscle cells as well as other normal cells. It looks like a double headed arrow with the two sets of heads pointing away from each other. Myosin moves along microfilaments by interacting with actin protein. It is also known as contractile protein as it helps in muscle contraction. It is also vital for cell division and cytoplasmic streaming. 18 different classes of myosin protein are known. Deficiency of Kinesin can cause Myopathies, Usher syndrome and deafness.

To summarise we can say that Kinesin and myosin belong to the molecular motor protein family. They aid in cellular and molecular transport of nutrients, metabolic products, organelles and vesicles by walking on tracks formed by the cytoskeleton.

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