Question

After an animal dies, its muscles start to stiffen before the decomposition of tissues relaxes the muscles again. Death is also characteized by calcium flow into the cytosol, due to breakdown of the sarcoplasmic reticulum. Which of the following would you expect to explain this muscle stiffening (i.e. rigor mortis)?

A. The myosin II heads in skeletal muscle fibers remain attached to actin filaments due to the absence of Ca2+ in these cells.
B. The ATPase activity of muscle myosin II is inhibited by the elevated Ca2+.
C. The myosin II heads in skeletal muscle cells remain attached to actin filaments due to the elevated Ca2+ in the muscle fibers.
D. Tropomyosin unfolds, preventing muscle relaxation.
E. The myosin II heads in skeletal muscle cells remain attached to actin filaments due to covalent cross-linking.

Answer 1

Muscle stiffening (rigor mortis) after an animal dies is due to the absence of ATP, which causes the myosin heads in skeletal muscle cells to remain attached to actin filaments. Calcium flow into the cytosol also contributes to muscle stiffness.

Step-by-step explanation:

After an animal dies, its muscles stiffen due to the absence of ATP, which is needed for muscle relaxation. In the absence of ATP, the myosin heads in skeletal muscle cells remain attached to actin filaments, causing muscle stiffness or rigor mortis. Calcium flow into the cytosol, due to the breakdown of the sarcoplasmic reticulum, also contributes to the muscle stiffening.