What is DNA ?

1. Nucleotides are the building stones of DNA.

There are 4 different nucleotides :
• dATP : deoxyadenosine triphosphate
• dGTP : deoxyguanosine triphosphate
• dTTP : deoxythymidine triphosphate
• dCTP : deoxycytidine triphosphate
For convenience, these 4 nucleotides are called dNTP's (deoxynucleoside triphosphates). A nucleotide is made of three major parts : a nitrogen base, a sugar molecule and a triphosphate. Only the nitrogen base is different in the 4 nucleotides.

Figure: The components of nucleotides. (pdf file of this picture)

2. How do the nucleotides form a DNA chain ?

Figure: From nucleotide to DNA. (pdf file of this picture) DNA is formed by coupling the nucleotides between the phosphate group from a nucleotide (which is positioned on the 5th C-atom of the sugar molecule) with the hydroxyl on the 3rd C-atom on the sugar molecule of the previous nucleotide. To accomplish this, a diphosphate molecule is split off (and releases energy). This means that new nucleotides are always added on the 3' side of the chain.