Yes, PEPTIDES is a Scrabble word!

Letter values in Scrabble US: P 3, E 1, P 3, T 1, I 1, D 2, E 1, S 1.

Is it a valid word?

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

amide combining the amino group of one amino acid with the carboxyl group of another; usually obtained by partial hydrolysis of protein