Once a nucleosome has formed on a particular stretch of DNA, how stable is it? Describe the processes---either passive or active---that can destabilize nucleosomes in vivo. Why is it important that nucleosomes can be destabilized?

The nucleosome is extremely stable.

Explanation:

The nucleosome when formed is extremely stable the histones are positively charged and the DNA wrapped around them are negatively charged, they have to be stable so as to be able to control the processes of replication, repair, transcriptional activities etc

Some processes including epigenetic mechanisms exist to destabilize the nucleosome. This is to help transcriptional machines fain access to the DNA for mRNA production. The nucleosome is so stabilized that it ensures transcriptional activities takes place at the only the right time and can also return back to its norrmal state when not needed.

Some processor that destabilize nucleosome includes

Acetylation: acetylation of some lysine residue on histone bring about destabilization: unwinding of the history from the DNA.

Histone chaperones: this too aids in the destabilization of the nucleosomes.

Topoisomerases activity: this helps in the unwinding of the DNA to allow transcriptional machineries to have access. ETC.

i'd think it's paralell