1. A purine base found in DNA and RNA that pairs with cytosine; one of the four nucleobases in genetic material.
Usage: biochemistry; genetics

Examples

• Guanin is one of the two purine bases in nucleic acids.
• The DNA sequence contains adenine, thymine, guanin, and cytosine.
• Guanin always pairs with cytosine in the double helix structure.
• Scientists study how guanin mutations can affect genetic expression.
• The guanin content of a genome varies between different organisms.