Final answer:
Actin is one of the most abundant proteins in eukaryotic cells, essential for cell structure and motility, and its polymers make up a significant portion of muscle tissue and the cytoskeleton.
Step-by-step explanation:
Actin is indeed one of the most abundant proteins in cells, making up a substantial percentage of the total cellular protein. This fact is supported by the actin gene family's large presence in the genome, which encodes various isoforms of this essential protein, predominant in cell structure and mobility.
Actin and myosin are particularly plentiful in muscle cells where they facilitate muscle contraction. Actin monomers (G-actin) polymerize to form actin filaments, which are powered by ATP to create long, twisted chains known as microfilaments or actin filaments. These filaments are a significant component of the cytoskeleton, functioning in cellular movement, and are especially narrow compared to other types of protein fibers such as microtubules and intermediate filaments.
A key feature of actin filaments is their polarity, which affects the rate of polymerization at either end. Cells harness this polarity and the dynamic nature of actin polymerization to generate force and movement, critical in various cellular processes such as division and motility.