Final answer:
Skeletal muscle cells appear striated due to the arrangement of actin and myosin filaments in sarcomeres. Sarcomeres contain regulatory proteins called troponin and tropomyosin, which play roles in muscle contraction by regulating the interaction between actin and myosin.
Step-by-step explanation:
The striated appearance of skeletal muscle cells is due to the arrangement of the myofilaments of actin and myosin in sequential order from one end of the muscle cell to the other. Each packet of these microfilaments and their regulatory proteins, troponin and tropomyosin, is called a sarcomere. In the sarcomere, actin and myosin filaments interact to cause muscle contraction.
Troponin and tropomyosin play important roles in regulating muscle contraction. Troponin is a complex of three proteins that binds calcium ions. When calcium is present, it causes a conformational change in troponin, which allows myosin to bind to actin and initiate muscle contraction. Tropomyosin, on the other hand, blocks the myosin binding sites on actin in the absence of calcium, preventing muscle contraction.