Microfilaments are composed of

The correct option is actin protein.

Step-by-Step Explanation:

1. Understanding Microfilaments:
Microfilaments, also known as actin filaments, are the thinnest fibers of the cytoskeleton found in the cytoplasm of eukaryotic cells. They play a critical role in cell movement, shape maintenance, and cell division.

2. Protein Composition:
Microfilaments are primarily composed of polymers of the globular protein actin (specifically G-actin, which polymerizes to form filamentous F-actin). These filaments are highly dynamic structures that can rapidly assemble and disassemble as needed by the cell.

3. Analyzing the Options:
- Mosaic protein: This is not a primary structural protein component of microfilaments.
- Tubulin protein: Tubulin is the building block of microtubules, which are larger, hollow cytoskeletal structures, not microfilaments.
- Chitin protein: Chitin is a polysaccharide (carbohydrate) that makes up the cell walls of fungi and the exoskeletons of arthropods, not a cytoskeletal protein.
- Actin protein: This is the correct structural component that polymerizes to form microfilaments.