Proteins can perform many different functions in living cells. one major function—acting as a catalyst for chemical reactions—can also be performed by what other kind of organic molecule?

Ribozymes can also act like catalysts.

Explanation:

Ribozymes are pieces or fragments of RNA that can act as catalysts of some reactions in the cell. These can bind RNA nucleotides without the action or presence of proteins and they can also be involved in the splicing process (deleting the introns).