What is meant by nucleated in this context? Hi I am little confused in one of my classes; because the teacher will say that " the actin is nucleated by the ARP 2/3 complex" or "microtubles are nucleated by the centrosome". Unless I am misunderstanding, I don't take this as having anything to do with the nucleus as in the nucleus inside a cell. ( or does it). so what does this really mean than? Thank you

Cytoskeletal nucleation refers to the _de novo_ formation of cytoskeleton filaments. If microtubules are nucleating, that means microtubules are being polymerized from lit. "From the beginning" by α/ß-tubulin dimers. So literally, and we see in the image below, Arp2/3 complexes act as progenitor sites so to say for new actin filaments by the "nucleation" of actin:

!enter image description here

From wikipedia for Nucleation: "Nucleation is the first step in the formation of either a new thermodynamic phase **or a new structure via self-assembly or self-organisation**."