All life on our planet, ALL of it, from bacteria to elephants to trees to humans to platypuses, uses a very specific system. DNA has a very specific structure that allows it to replicate itself and synthesis proteins, and allow life to form. Furthermore all of these molecules are organised into cells.

This very specific chemistry of life is unlikely to arise on another planet, and even if it did, it is extremely unlikely that the life forms would evolve like life did on Earth. So chances are, these alien organisms, even if they existed, would probably be microorganisms and primitive multicellular organisms. Certainly they would be adapted to conditions that are very different from those on our planet.

On the other hand, maybe there is life that uses an entirely different system for biology that is too alien and bizarre for us to imagine.