What is Protein Synthesis?

Protein Synthesis :  Protein synthesis begins in the nucleus, with the formation of mRNA from a DNA template through transcription. The function of mRNA is really to magnify the amount of protein that can be made from a single strand of DNA. If DNA were used directly to manufacture protein, a single gene would be limited in the amount of protein that could be translated from it, since proteins are generally coded in only one copy. Many copies of mRNA can be made, and these can be used to synthesize a large amount of protein when it is needed quickly. Sometimes, tens of thousands of copies can be functioning in the cell for each copy of the message coded on DNA.

Information for a polypeptide chain is stored in DNA in sequences of three nucleotide bases, each of which specifies a single amino acid. Messenger RNA is therefore also organized into groups of three bases, called codons, each of which specifies a single amino acid or a signal to start or stop replication. The sequence AUG is the start code for translation; UGA, UAA, and UAG are stop codes. The remaining permutations and combinations of bases code for the 20 different amino acids. Since there are 64 codons and 20 amino acids, each amino acid can be formed from two or more codons. Each mRNA codes for only one amino acid chain, or polypeptide.

After formation, mRNA strands move out of the nucleus through nuclear pores into the cytoplasm, where it then moves into a group of ribosomes. Several ribosomes can be translating the same mRNA strand simultaneously. There, mRNA serves as a template upon which tRNA molecules bring the proper amino acids into order to form a growing polypeptide chain. This process is called translation. Translation includes the processes of initiation, elongation, and termination and breakup of mRNA.