At what point do particles become "alive"

Are there any theories that all life only carries out its functions to achieve atomic/nuclear/molecular stability? Like, we are not really alive and only act on instinct.

I admit they have lost some molecular machinery over the time of being engulfed in another organism

Not to my knowledge, but life is real interested in replication. I suppose in some way the idea of keeping oneself in existence (even if just through one's children) is a form of stability.

Something is alive when/if it is made up of at least one cell, can respond to external stimuli, and produce offspring.

T. Highschool biology teacher