Which two protein filaments make up a sarcomere?

Which two protein filaments make up a sarcomere?

• A. Titin and Nebulin
• B. Myosin and Actin
• C. Dystrophin and Spectrin
• D. Collagen and Elastin

Answer: (B)

The main idea is that the contractile machinery of a sarcomere is built from actin and myosin filaments. Thin filaments made of actin extend from the Z discs toward the center, while thick filaments made of myosin reside in the middle and overlap with actin. During contraction, myosin heads bind to actin and, powered by ATP hydrolysis, pull the actin filaments toward the center of the sarcomere. This sliding filament interaction shortens the sarcomere and, in turn, the muscle fiber. Other proteins you might hear about have supportive roles but aren’t the primary contractile filaments. Titin acts as an elastic spring linking Z discs to the M line to stabilize and reset the sarcomere; Nebulin helps determine thin-filament length; Dystrophin and spectrin are part of the membrane cytoskeleton; Collagen and elastin are extracellular matrix components.

The main idea is that the contractile machinery of a sarcomere is built from actin and myosin filaments. Thin filaments made of actin extend from the Z discs toward the center, while thick filaments made of myosin reside in the middle and overlap with actin. During contraction, myosin heads bind to actin and, powered by ATP hydrolysis, pull the actin filaments toward the center of the sarcomere. This sliding filament interaction shortens the sarcomere and, in turn, the muscle fiber.

Other proteins you might hear about have supportive roles but aren’t the primary contractile filaments. Titin acts as an elastic spring linking Z discs to the M line to stabilize and reset the sarcomere; Nebulin helps determine thin-filament length; Dystrophin and spectrin are part of the membrane cytoskeleton; Collagen and elastin are extracellular matrix components.