By Robert Mullis – Updated Mar 24, 2022
Ribonucleic acid (RNA) is indispensable to every living cell. It drives the central dogma—transcription of DNA into RNA, followed by translation of RNA into proteins. There are three principal RNA species, each with a distinct role: messenger RNA (mRNA) conveys genetic instructions to the ribosome; ribosomal RNA (rRNA) forms the structural and catalytic core of ribosomes; and transfer RNA (tRNA) decodes mRNA codons into amino acids.
Unlike DNA’s deoxyribose backbone, RNA contains ribose, making it chemically reactive and typically single‑stranded. RNA uses uracil instead of thymine, and its flexible three‑dimensional folds confer functional versatility. These properties enable RNA to act as messenger, catalyst, and adaptor in cellular biochemistry.
Transcription is mediated by RNA polymerase, which reads a DNA template and synthesizes a complementary RNA strand. Regulatory elements—promoters, enhancers, and inhibitors—precisely control this process. All three RNA types are produced via transcription, followed by specific post‑transcriptional modifications.
mRNA bridges DNA and protein. After transcription, it exits the nucleus and undergoes cap addition, polyadenylation, and intron removal (splicing). In the cytoplasm, ribosomes read the mRNA sequence, translating codons into polypeptide chains with tRNA assistance.
rRNA, together with ribosomal proteins, assembles into the large and small ribosomal subunits. rRNA provides both structural scaffolding and catalytic activity—its peptidyl‑transferase center catalyzes peptide bond formation during translation.
tRNA molecules serve as adaptors between mRNA codons and amino acids. Each tRNA bears an anticodon that base‑pairs with a specific mRNA codon and carries the corresponding amino acid. Modifications such as pseudouridine, inosine, and methylguanosine fine‑tune tRNA function.
