Question Video: Identifying Tropomyosin in a Diagram of Myofilaments | Nagwa Question Video: Identifying Tropomyosin in a Diagram of Myofilaments | Nagwa

Question Video: Identifying Tropomyosin in a Diagram of Myofilaments Biology • Third Year of Secondary School

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The sliding filament theory outlines the process of muscle contraction. The diagram provided shows the basic outline of a myosin and an actin filament before they have bound. Which structure is indicated by X?

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Video Transcript

The sliding filament theory outlines the process of muscle contraction. The diagram provided shows the basic outline of a myosin and an actin filament before they have bound. Which structure is indicated by X? (A) Sarcolemma, (B) tropomyosin, (C) collagen, or (D) myosin-binding sites.

To answer this question, let’s take a look at the filament shown in this diagram in a bit more detail. Muscle fibers generally contain three types of protein filament: actin, myosin, and tropomyosin.

Actin is a thin filament consisting of two strands twisted around each other. Myosin is a thicker filament with globular heads that project outward. Tropomyosin coils around each actin filament. The muscle fiber shown in the image provided by the question is in a relaxed state. When a muscle fiber is relaxed, tropomyosin blocks the binding sites for the myosin heads that are present on the surface of each actin filament. This prevents the myosin heads from binding to the actin filament.

During muscle contraction, calcium ions pull away tropomyosin from these binding sites, allowing myosin to bind to the actin filaments. This triggers a series of events that pulls the actin filaments, overall resulting in a shortened, contracted muscle fiber.

Using the information we have learned, we can answer this question correctly. The structure in the diagram indicated by X is (B) tropomyosin.

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