A carbohydrate is a biological molecule consisting of carbon (C), hydrogen (H) and oxygen (O) atoms, usually with a hydrogen–oxygen atom ratio of 2:1 (as in water) in other words, with the empirical formula Cm(H2O)n (where m could be different from ). Some exceptions exist; for example, deoxyribose, a sugar component of DNA, has the empirical formulaC5H10O4. Carbohydrates are technically hydrates of carbon; structurally it is more accurate to view them as polyhydroxy aldehydes and ketones.