deoxyribose versus ribose
/ dee-OK-see-RY-bose / RY-bose /
DNA and RNA differ in their names by just one syllable — the 'deoxy' in DNA — and that one syllable names a difference of a single oxygen atom on a sugar. It is a tiny chemical change with outsized consequences.
Both DNA and RNA use a five-carbon ring sugar. RNA's sugar is ribose, which carries an oxygen-hydrogen group (an OH, a hydroxyl) on the carbon numbered 2'. DNA's sugar is deoxyribose, which is ribose with that 2' oxygen removed — 'deoxy' literally means 'minus an oxygen'. So the only structural difference between the sugars is one OH at the 2' position: present in ribose, absent in deoxyribose. That is the D-versus-R in DNA and RNA.
This single missing oxygen explains a great deal. The extra 2' OH on ribose makes RNA more chemically reactive and far less stable — RNA can attack its own backbone and break, which is partly why RNA is a short-lived working copy while DNA is the durable master archive. The missing oxygen makes DNA tougher and longer-lasting, fit to store information for the life of a cell, and even across generations and geological time.
Ancient DNA has been read from bones tens of thousands of years old; no one expects to recover intact ancient RNA the same way, because that reactive 2' hydroxyl makes RNA fall apart far sooner.
One oxygen at 2' separates the durable archive from the working copy.
The 'deoxy' refers specifically to the 2' carbon, not just 'any missing oxygen'. Both sugars still carry the 3' OH that links nucleotides together; only the 2' position differs between them.