Protein synthesis is the process whereby proteins are produced, or synthesized, in living things according to "directions" given by DNA (deoxyribonucleic acid) and carried out by RNA (ribonucleic acid) and other proteins. As suggested earlier, this is an extraordinarily complex process that we do not attempt to discuss here. Following synthesis, proteins fold up into an essentially compact three-dimensional shape, which is their tertiary structure. DNA contains the instructions for a cell's structure and function. It is the blueprints for how the cell runs, reproduces, builds and repairs itself, and every other function necessary for cell life. Messenger ribonucleic acid (mRNA) is a molecule of ribonucleic acid (RNA) that encodes the correct sequence of amino acids in a protein. tRNA is used to carry the 20 different amino acids dissolved in the cytoplasm to the ribosomes to help build the polypeptide chain for proteins to be synthesized. rRNA (or ribosomal RNA) combines with proteins to form ribosomes that serve as the site of protein synthesis. It unzips the DNA helix and transcription begins. Transcription is the first step of gene expression, in which a particular segment of DNA is copied into RNA by theenzyme RNA polymerase. Both RNA and DNA are nucleic acids, which use base pairs of nucleotides as acomplementary language that can be converted back and forth from DNA to RNA by the action of the correct enzymes. During transcription, a DNA sequence is read by an RNA polymerase, which produces a complementary, antiparallelRNA strand. Translation requires tRNAs, which bring in amino acid and line them up according to the genetic code in mRNA. Translation include three steps: Initiation: the ribosome subunit binds to 5’ end of mRNA. Elongation: an incoming aminoacyl-tRNA binds to codon at A-site, peptide bond is formed between new amino acid and growing chain. The peptide moves one codon position and gets ready for next one. Stop codons is not recognized by any tRNA.