Nucleic bases are nitrogenous bases. They are: adenine, guanine, thymine and cytosine in DNA and uracil in place of thymine in RNA. Nitrogenous bases are arranged across the DNA strands. Following the Central Dogma, DNA converts to RNA by transcription and RNA to proteins by translation.
After the transcription process mRNA is formed. This mRNA is used for protein synthesis with the help of ribosomes. The three nitrogen sequences that codes for amino acid are called as codons.
Synthesis of amino acids are read in triplets. The codons that start the translation process are called as start codon and the ones that stop the translation process are Stop codons.