DNA versus RNA
/ dee-en-AY / ar-en-AY /
DNA and RNA are the two nucleic acids, and they are close cousins with a clear division of labor. The simplest way to think about it: DNA is the master archive, the library copy that stays safe; RNA is the working photocopy, the disposable note you carry to the workbench.
Both are chains of nucleotides, but they differ in three telling ways. First, the sugar: DNA's sugar (deoxyribose) is missing one oxygen compared with RNA's (ribose) — which is literally where the D in DNA comes from. Second, one base: DNA uses thymine (T), while RNA uses uracil (U) in its place. Third, and most visible, DNA is usually a double strand — the famous double helix, two strands held together by base-pairing — whereas RNA is usually a single strand. That extra oxygen and missing second strand make RNA more reactive and shorter-lived, while DNA is built to last.
The roles follow from the chemistry. DNA's stability suits it to store the genome safely for the lifetime of a cell and to be copied faithfully to the next generation. RNA's disposability suits it to carry temporary messages: a cell copies a gene from DNA into RNA, uses that RNA to build a protein, then discards it. Long-term memory versus short-term working notes — same alphabet, two very different jobs.
Many vaccines use a strand of RNA precisely because RNA is short-lived: it delivers its instructions, the cell makes the protein, and then the RNA quickly breaks down and disappears.
RNA's short lifespan — a drawback for an archive — is exactly the point in an mRNA vaccine.
The double helix is a property of typical DNA, not of nucleic acids in general: most RNA is single-stranded, and that single fact shapes much of what RNA can and cannot do.