Chemical structure of guanine, showing its double-ring purine structure and the functional groups involved in hydrogen bonding with cytosine. (Image: Public Domain) Guanine has the chemical formula ...

Other combinations of the atoms form the four bases: thymine (T), adenine (A), cytosine (C), and guanine (G). These bases are the rungs of the DNA ladder. (It takes two bases to form a rung -- one ...