There are three hydrogen bonds formed between Guanine and Cytosine base.
The first hydrogen bond is formed between the oxygen atom on Carbon-6 (C-6) of guanine, and one of the hydrogen atoms attached to the Nitrogen atom (i.e the one of the hydrogen atoms in the amino group) on the Carbon-4 (C-4)of the cytosine base.
The second hydrogen bond is formed between the hydrogen atom on Nitrogen-1 (N-1) of the guanine base and Nitrogen-3 (N-3) of the cytosine base.
The third hydrogen bond exist between one of the hydrogen atoms in the amino group attached to the second Carbon (C-2) of the guanine base, and the oxygen atom attached to the second Carbon (C-2) of the cytosine base.
