Final answer:
A sarcomere is composed of two myofilaments: thick filaments and thin filaments. Thick filaments consist of myosin, while thin filaments consist of actin. These myofilaments work together in muscle contraction.
Step-by-step explanation:
A sarcomere, the smallest contractile portion of a muscle, is composed of two myofilaments: thick filaments and thin filaments. Thick filaments are composed of the protein myosin, while thin filaments are composed of the protein actin. These myofilaments work together in muscle contraction. The thick filaments contain multiple myosin molecules with protruding heads that interact with the thin filaments, causing them to slide and the sarcomere to contract.