Which statement about the sarcomere bands is true?

Which statement about the sarcomere bands is true?

• A. The I-band contains thick filaments only.
• B. The A-band contains thin filaments only.
• C. The I-band contains thin filaments; the A-band contains thick filaments and overlapping thin filaments.
• D. The I-band is the site of myosin-actin overlap during contraction.

Answer: (C)

Filament arrangement in a sarcomere defines the bands: the I-band contains only thin actin filaments, while the A-band spans the full length of the thick myosin filaments and includes regions where thin filaments overlap with thick filaments. This makes the statement that the I-band contains thin filaments true, and the A-band contains thick filaments plus overlapping thin filaments true as well. The I-band does not contain thick filaments, and the site where actin and myosin overlap occurs within the A-band, not the I-band. During contraction, the I-band shortens as actin filaments slide inward, while the A-band length stays constant because the lengths of the filaments themselves don’t shorten.

Filament arrangement in a sarcomere defines the bands: the I-band contains only thin actin filaments, while the A-band spans the full length of the thick myosin filaments and includes regions where thin filaments overlap with thick filaments. This makes the statement that the I-band contains thin filaments true, and the A-band contains thick filaments plus overlapping thin filaments true as well. The I-band does not contain thick filaments, and the site where actin and myosin overlap occurs within the A-band, not the I-band. During contraction, the I-band shortens as actin filaments slide inward, while the A-band length stays constant because the lengths of the filaments themselves don’t shorten.