Do you need specific sources on this for a paper? I️ would use easybib it is a great source to get bibliographies done quick.
        
             
        
        
        
Its ready to begin prophase
        
             
        
        
        
Okay, biology isn't exactly my strongest subject (it never has been), but I'm pretty sure the answer is nucleotides. DNA is made up of nucleotides. Each nucleotide contains a phosphate group, a sugar group, and a nitrogen base. There are four different nitrogen bases: adenine (A), thymine (T), guanine (G), and cytosine (C). A always pairs with T, and G always pairs with C.