Final answer:
Actin and myosin are the proteins responsible for muscle contraction, following the sliding filament model and powered by ATP. The correct option is A.
Step-by-step explanation:
The proteins responsible for the contraction of a muscle are actin and myosin. In striated muscles, such as skeletal and cardiac muscles, actin and myosin interact to cause muscle contraction through the sliding filament model. The process begins when calcium ions (Ca++) bind to regulatory proteins troponin and tropomyosin, which then expose binding sites on actin filaments.
Myosin heads attach to these sites and pull the actin filaments, leading to muscle contraction. This process is powered by adenosine triphosphate (ATP), and the muscle relaxes when calcium ions are removed, causing the actin binding sites to be covered again.