Final answer:
The three classes of functional RNAs are mRNA, which carries genetic instructions from DNA; rRNA, which forms ribosomes that assemble proteins; and tRNA, which brings amino acids to the ribosome for protein synthesis.
Step-by-step explanation:
The three classes of "functional" RNAs are messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA). mRNA serves the pivotal role of copying genetic instructions from DNA and conveying them to the cytoplasm for protein synthesis. rRNA is a key structural and enzymatic component of ribosomes, where it aids in the assembly and function of these protein-synthesizing factories. tRNA brings the appropriate amino acids to the ribosome, matching the sequence specified by the mRNA, and facilitates the proper assembly of the protein being synthesized.
mRNA acts as a template for translating genetic codes into proteins by specifying the order in which amino acids should be added to the growing polypeptide chain. rRNA forms the core of ribosome's structure and catalyzes protein synthesis. tRNA acts like an adaptor molecule, helping to translate the mRNA codons into the actual amino acids they encode during the process known as translation, which completes the final step of expressing genetic information into functional proteins.