The thin filament of a muscle fibril is made of two filamentous strands of

1. Each thin filament is built from a repeating protein. 2. It is made of two filamentous, or F, actins helically wound to each other. 3. Each F actin is itself a polymer of monomeric G actins. 4. Tropomyosin runs alongside the actins, and troponin sits on the tropomyosin. 5. Myosin belongs to the thick filament, not the thin one. _Source: syllabus Biology Ch17 'Locomotion and Movement'_