<P> Nucleotides are commonly abbreviated with 3 letters . The first letter indicates the identity of the nitrogenous base (e.g. A for adenine, G for guanine), the second letter indicates the number of phosphates (mono, di, tri), and the third letter is P, standing for phosphate . Nucleoside triphosphates that contain ribose as the sugar are conventionally abbreviated as NTPs, while nucleoside triphosphates containing deoxyribose as the sugar are abbreviated as dNTPs . For example, dATP stands for deoxyribose adenosine triphosphate . NTPs are the building blocks of RNA, and dNTPs are the building blocks of DNA . </P> <P> The carbons of the sugar in a nucleoside triphosphate are numbered around the carbon ring starting from the original carbonyl of the sugar . Conventionally, the carbon numbers in a sugar are followed by the prime symbol (') to distinguish them from the carbons of the nitrogenous base . The nitrogenous base is linked to the 1' carbon through a glycosidic bond, and the phosphate groups are covalently linked to the 5' carbon . The first phosphate group linked to the sugar is termed the α - phosphate, the second is the β - phosphate, and the third is the γ - phosphate . </P> <P> The cellular processes of DNA replication and transcription involve DNA and RNA synthesis, respectively . DNA synthesis uses dNTPs as substrates, while RNA synthesis uses NTPs as substrates . It should be noted that NTPs cannot be converted directly to dNTPs . DNA contains four different nitrogenous bases: adenine, guanine, cytosine and thymine . RNA also contains adenine, guanine, and cytosine, but replaces thymine with uracil . Thus, DNA synthesis requires dATP, dGTP, dCTP, and dTTP as substrates, while RNA synthesis requires ATP, GTP, CTP, and UTP . </P> <P> Nucleic acid synthesis is catalyzed by either DNA polymerase or RNA polymerase for DNA and RNA synthesis respectively . These enzymes covalently link the free - OH group on the 3' carbon of a growing chain of nucleotides to the α - phosphate on the 5' carbon of the next (d) NTP, releasing the β - and γ - phosphate groups as pyrophosphate (PPi). This results in a phosphodiester linkage between the two (d) NTPs . The release of PPi provides the energy necessary for the reaction to occur . It is important to note that nucleic acid synthesis occurs exclusively in the 5' to 3' direction . </P>

Atp is the primary building block of dna