The steps of protein synthesis, the process by which genetic information is converted into proteins, are transcription, translation, and in some cases, posttranslational modification and protein folding. Proteins are functional biological units composed of folded biochemical chains that are involved in almost every chemical process that takes place within the body, including immune response, digestion, and cell growth. They also play a structural role in many organisms and are responsible for maintaining the shapes and positions of many cells, tissues, and organs. Different proteins must be produced in correct ratios with correct timing, so it is important that the steps for synthesizing them run in a coordinated and precise manner.
Transcription is the first of the major steps in making proteins. In transcription, genetic information in the form of double-stranded deoxyribonucleic acid, or DNA, is “read” by a group of proteins that create a single-stranded ribonucleic acid, or RNA, transcript. Proteins begin and end the process of transcription at specific points on a strand of DNA based on the genetic information encoded in the strand. The specific start and stop points determine the identity of the protein that will later be produced. The DNA strand is preserved in transcription, so many RNA transcripts can be produced from a single DNA strand.
The next of the major steps of protein synthesis is referred to as translation, which is when the protein itself is produced; the other steps involve either producing the transcript that contains information for the protein or modifying the protein after it is produced. In translation, the RNA transcript is surrounded by ribosome, or the “protein factory” that “reads” the genetic information on the transcript to produce a polypeptide chain. This chain, before folding, is simply a string of amino acids. Either spontaneously or with the assistance of other proteins, the amino acid chain later folds and takes on the three-dimensional structure from which the functions of proteins are derived.
Although the protein is produced in translation, sometimes there are further steps necessary for protein synthesis that ensure that the protein is well suited for its eventual purpose. Protein folding, for example, is generally not completed until after translation is complete. Additionally, in some cases, other proteins perform chemical modifications on the newly-produced unit. These alterations tend to change the three-dimensional structure of the protein, thereby altering its function. Other forms of posttranslational modification also may reversibly activate or deactivate the newly produced protein.