 In all known organisms , the Deoxyribonucleotides that make up DNA are synthesized by the action of ribonucleotide reductase ( RNR ) enzymes on their corresponding ribonucleotides . These enzymes reduce the sugar residue from ribose to deoxyribose by removing oxygen from the 2 ′ hydroxyl group ; the substrates are ribonucleoside diphosphates and the products deoxyribonucleoside diphosphates ( the latter are denoted dADP , dCDP , dGDP , and dUDP respectively . ) All ribonucleotide reductase enzymes use a common sulfhydryl radical mechanism reliant on reactive cysteine residues that oxidize to form disulfide bonds in the course of the reaction . RNR enzymes are recycled by reaction with thioredoxin or glutaredoxin . 
