|University Federico II
of Naples, Italy
Nucleic acids are polymers, i.e. molecules made up of a large number of smaller units: nucleotides. A nucleotide is made of three units, that are named sugar, phosphate and nitrogen base. If we compare the DNA strand to a long train, the three units are like three compartments making up a carriage of the train.
The main difference between the two kinds of nucleic acids is in sugars. RNA contains a sugar called ribose, whereas DNA contains deoxyribose. Deoxyribose is like ribose, except it lacks the oxygen atom at the 2' carbon atom (the second from right).
The sequence of a nucleic acid is made by four different nucleotides, that are distinguished by their base. DNA contains the four bases Cytosine, Thymine, Adenine and Guanine (often shortened as C T A G).
Cytosine Thymine Adenine Guanine
Nucleic acids are also different in their base composition. Three bases: C A G are common to both. RNA contains no Thymine; it contains Uracil instead.