What is RNA?

RNA is similar to DNA but typically single-stranded and uses the base uracil (U) instead of thymine (T). Messenger RNA (mRNA) copies instructions from DNA and carries them to ribosomes, where transfer RNA (tRNA) helps translate the code into proteins. Ribosomal RNA (rRNA) forms the core of the ribosome itself. Other types, like microRNA and long non-coding RNA, regulate gene expression. RNA is also central to some viruses, including influenza, HIV and SARS-CoV-2. The mRNA COVID-19 vaccines work by delivering synthetic mRNA that teaches cells to make a viral protein and trigger an immune response.