Myofibrils are what?

Myofibrils are what?

• A. Nuclei
• B. Ribosomes
• C. Mitochondria
• D. Microscopic protein filaments that make up muscle cells

Answer: (D)

Myofibrils are the contractile elements inside muscle fibers, built from long, organized protein filaments arranged into repeating units called sarcomeres. The core filaments are actin (thin) and myosin (thick), which slide past each other during contraction to shorten the muscle. That’s why they’re described as microscopic protein filaments that make up muscle cells. They aren’t nuclei (which house genetic material), ribosomes (protein-making machines), or mitochondria (the cell’s ATP factories).

Myofibrils are the contractile elements inside muscle fibers, built from long, organized protein filaments arranged into repeating units called sarcomeres. The core filaments are actin (thin) and myosin (thick), which slide past each other during contraction to shorten the muscle. That’s why they’re described as microscopic protein filaments that make up muscle cells. They aren’t nuclei (which house genetic material), ribosomes (protein-making machines), or mitochondria (the cell’s ATP factories).