Final answer:
Francis Crick proposed the adaptor hypothesis involving transfer RNA (tRNA) in the process of translation, where tRNA transfers specific amino acids to the ribosome to be incorporated into a polypeptide chain according to the genetic code.
Step-by-step explanation:
Francis Crick proposed that certain types of RNA molecules were involved in the incorporation of amino acids into a polypeptide chain during the process of translation in cells. Specifically, Crick hypothesized the role of transfer RNA (tRNA) molecules in this process. tRNA functions as an adaptor molecule that interprets the genetic information encoded in messenger RNA (mRNA) and brings the corresponding amino acid to the growing polypeptide chain in the ribosome. Each tRNA molecule has an anticodon that matches the codon on the mRNA, ensuring that the correct amino acid is incorporated into the polypeptide chain according to the genetic code.