Adenine and guanine are purines, cytosine and uracil are pyrimidines. It consists of 4 nucleotides guanine, thymine, cytosine, and adenine. Cytosine is deaminated to uracil, which base pairs with Adenine instead of Guanine. Its growth requires presence of nicotinamide adenine dinucleotide. Nicotinate salvage is the process of regenerating nicotinamide adenine dinucleotide from nicotinic acid. Uracil pairs with adenine through hydrogen bonding. In RNA, uracil base-pairs with adenine and replaces thymine during DNA transcription. Some NAD is converted into the coenzyme nicotinamide adenine dinucleotide phosphate (NADP). In cells, nicotinamide is incorporated into NAD+ and nicotinamide adenine dinucleotide phosphate (NADP). It can cause deamination of the amino groups of Adenine, Guanine and Cytosine. Adenine pairs with thymine and guanine pairs with cytosine, forming A-T and G-C base pairs. Purine metabolism involves the formation of adenine and guanine. Some strains also required a combination of uracil, guanine, adenine and xanthine. The others are adenine, guanine, and cytosine. Scientists knew there was a total of four bases (guanine, cytosine, adenine, and thymine).