Guanine

• Guanine, a nitrogenous organic base of DNA, is a biological molecule that bonds with other DNA sequence types. It bonds with hydrogen and cytosine, which is another type in the DNA sequence. Guanine will only pair with cytosine. Guanine (2-amino-6-oxypurine) is also a purine derivative. The nucleoside is known as guanosine. It is responsible for signal transduction of cells, protein transport and growth regulation.
  
  

Cytosine

• Cytosine, also a nitrogenous organic base of DNA, is a molecule that bonds with other biological molecules. Called a pyrimidine, it bonds with the DNA sequence type Guanine. Cytosine is only able to bond with hydrogen and in the presence of guanine. This forms part of the nitrogenous base of cells and DNA. It is known as a "complementarity" process because it is the basis of the sequence of DNA.
  
  

Thymine

• Thymine, like guanine and cytosine, is a nitrogenous organic base of DNA. It also has a function in other biological molecules. It is called a pyrimidine, which means it has a specific bond. It only bonds to adenine in the DNA molecule. Unlike other sequence types, it will not bond with RNA.
  
  

Adenine

• Adenine is a base that comprises both DNA and RNA nucleotides. It is different from thymine because it is a component of the bond with RNA as well. It also bonds in complex processes with other molecules in the biological makeup of all living things. It is considered a purine and will bond only to thymine. Unlike other DNA sequence types, it bonds to a non-nitrogenous base called uracil in RNA.