Yes, EPISOME is a Scrabble word!

Letter values in Scrabble US: E 1, P 3, I 1, S 1, O 1, M 3, E 1.

Is it a valid word?

EPISOME is a valid word in the official Scrabble dictionary (US), the UK Scrabble Dictionary and Words with Friends (ENABLE).

DNA that is not incorporated into the genome but is replicated together with the genome (especially in bacterial cells)