University Federico II
of Naples, Italy
European Chemistry
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Nucleic acids

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).

Ribose Deoxyribose

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.