Actin Filaments That Are Held Together by the Cross-Linking Protein

question 39

Multiple Choice

Actin filaments that are held together by the cross-linking protein fimbrin are not contractile. This is probably because …

• A) the very weak cross-linking by this protein cannot convert myosin II activity into a coherent contraction.
• B) fimbrin arranges the actin filaments in parallel bundles in which all the plus ends point to the same direction.
• C) the very tight packing of actin filaments by this small protein excludes myosin II filaments and other large proteins.
• D) fimbrin arranges the actin filaments into gel-like networks in which myosin II activity does not produce contraction.
• E) fimbrin is a large protein that binds to several actin filaments and resists contraction.