Genetic code is a set of biochemical instructions by which living cells translate information encrypted in DNA or RNA sequences into amino acids sequences.
The genetic code contains sequence of three codons written along the length of DNA strand. Each genetic code is a specific combination of three letters. The 64 possible code words are formed from the four letters A (adenine), C (cytosine), G (guanine), T (thymine).
The codes in the coding strand DNA and in messenger RNA are not alike because in RNA, the uracil base substitutes thymine base and ribose substitutes deoxyribose.
The codon that designates the start of a protein chain is AUG, which is the amino acid methionine. The codons that designate the end of the chain are UAA, UAG,UGA.