What large contractile protein contributes to the movement of cilia and flagella?

Dynein is a large contractile protein that plays a crucial role in the movement of cilia and flagella. These structures are essential for cellular locomotion and movement of fluids across cell surfaces. Dynein functions by utilizing ATP to generate force that causes microtubules, which are part of the cilia and flagella's structural framework, to slide against each other. This sliding action results in the bending and the undulating movement characteristic of cilia and flagella.

Moreover, dynein is part of a complex arrangement called the axoneme in cilia and flagella, where its interaction with another protein, nexin, allows for coordinated motion. The unique structure and the protein’s ability to convert chemical energy from ATP into mechanical energy underpin the dynamic movements necessary for their function.

In contrast, actin and myosin are primarily involved in muscle contraction and cell motility through different mechanisms, while kinesin serves mainly to transport cellular cargo along microtubules instead of generating movement in cilia and flagella. Thus, dynein's specific role in the movement mechanisms of these organelles makes it the correct answer.