Which statement about muscle contractile proteins is true?
A) Three chains of actin monomers twisted together form an actin filament.
B) A molecule of myosin consists of two long linear polypeptide chains each with a globular head.
C) A myosin filament consists of a single myosin molecule with its heads projecting at the ends of the filament.
D) The polypeptides that make up actin have globular heads.
E) Tropomyosin twists around the myosin molecule.

Question

Quizplus · Accepted Answer

A molecule of myosin consists of two long linear polypeptide chains each with a globular head. This allows for the heads to interact with the actin filaments during muscle contraction.

Note: Choice A is incorrect because actin filaments are made up of two chains of actin monomers twisted together, not three. Choice C is incorrect because a myosin filament consists of many myosin molecules arranged in a staggered fashion, not a single molecule. Choice D is incorrect because the polypeptides that make up actin do not have globular heads, but instead form the structure of the filament. Choice E is incorrect because tropomyosin is a separate protein that blocks the binding sites of actin during muscle relaxation.

Which Statement About Muscle Contractile Proteins Is True