Final answer:
CapZ binds to the plus ends of actin microfilaments, thereby preventing both assembly and disassembly, which stabilizes the length of the filaments.
Step-by-step explanation:
The correct option is C) prevents assembly and disassembly at microfilament plus ends. CapZ is a protein that binds to the plus ends of actin filaments, also known as microfilaments, thereby preventing further addition or loss of actin subunits at that end. The presence of CapZ essentially caps the microfilament's plus end, stabilizing its length and preventing dynamic changes in polymerization state which would otherwise lead to growth or shrinkage.
Actin microfilaments are renowned for their dynamic instability, largely driven by ATP-dependent conformational changes in actin monomers. These monomers add onto filaments preferentially at their plus ends, where they are ATP-bound, allowing for quick assembly. Once integrated into the microfilament, the bound ATP is hydrolyzed to ADP within seconds, decreasing the binding affinity of the monomers and making the filament prone to disassembly at the minus end. This treadmilling effect is crucial for cellular processes but can be modulated by capping proteins like CapZ, which blocks the dynamic behavior specifically at the plus end.