A General Description of Protein Biosynthesis

The information contained in genes is expressed, in part, by the proteins that are within a cell. The genes contain information for their own replication, for the synthesis of other nucleic acids and proteins including enzymes, and for the various control mechanisms of protein biosynthesis. 

DNA carries out two functions (1) it provides for its own exact replication, thus permitting genetic continuity and (2) it directs the linear sequence of amino acids in proteins on the basis of the linear sequence of nucleotides in the DNA. This latter function is carried out by the process of transcription, during which the genetic message in DNA is expressed in the various classes of RNA (viz., messenger, transfer, and ribosomal RNA). 

In like manner, ribosomal ribonucleic acid (rRNA) and transfer ribonucleic acid (tRNA) are synthesized from their specific genes through the action of DNA-dependent RNA polymerase. And as in the case of mRNA, each of the precursor forms of these nucleotides are also processed until they reach their final forms. The rRNAs and a large variety of ribosomal proteins are assembled to form the ribosome. Ribosomes, the supramolecular structures in which protein synthesis takes place and which functionally resemble multienzyme complexes, are elaborate structures. They are attached, by a binding site on the smaller subribosomal particle, to the endoplasmic reticulum. The tRNAs that are synthesized finally become charged with specific amino acids. 

Translation from the linear sequences of mRNA into proteins is an extremely complex process, as befits the requirement for fidelity at all stages of the process. The translational keys to the process are the tRNA molecules, which are akin to the Rosetta stone. These specific adaptor molecules (tRNA) are responsible for aligning each amino acid with its specific mRNA codon, and tRNA molecules thus read the information in both mRNA and in amino acids. 

The various mRNAs become attached to the assembled ribosomes and order the sequence of amino acids that are attached to the tRNAs. 

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