I need to figure out the structure of an unknown organism and what the main type of cell it is by only knowing: Organism’s cell are able to move Internal structures appears to be made of protein fibers Internal structures protein fibers measured 7.0 nanometers diameter Internal structures protein fiber appears to be two strands intertwined with each others

Explanation:

In eukaryotic cells, the cytoskeleton is composed of three well defined filamentous structures: microtubules, microfilaments, and intermediate filaments. Each of these filamentous structures is a polymer of proteinic subunits united by weak, not covalent connections.

The microfilaments are the thinnest of the three structures. They have a diameter of 7 nanometers and are composed of many proteinic monomers united. This monomeric protein is called actin. Many monomers get combined to form a structure that assembles a double helix.

Due to the fact that these microfilaments are made of actin monomers, they are also known as actin filaments.

Actin filaments have directionality which means that their extremes have different structures.  

Microfilaments interact with myosin filaments. These are associated with transmembrane proteins that have one domain in the cytosol and another in the cell exterior, therefore they participate in the processes of cell mobility.