Final answer:
The sarcomere is the fundamental unit of a skeletal muscle fiber, comprising the region between two Z-discs or Z-lines. It contains the actin and myosin proteins that enable muscle contraction, and its repeated arrangement within myofibrils gives muscles a striated appearance.
Step-by-step explanation:
In a skeletal muscle fiber, the sarcomere is a repetitive unit that consists of the entire region between two consecutive Z-discs or Z-lines. The sarcomere, defined as the space from one Z-line to the next, is the basic functional unit responsible for muscle contraction. Muscles display a striated appearance due to the alignment of sarcomeres within the myofibrils, which contain the contractile proteins actin and myosin.
These proteins interact to facilitate muscle contraction, with myosin forming the thick filament and actin the thin filament of the sarcomere. The alternating pattern of dark A bands and light I bands, resulting from the arrangement of sarcomeres, gives skeletal muscle its characteristic striated look.