Biosynthesis of Proteins

Protein synthesis is the creation of proteins. In biological systems, it is carried out inside the cell. In prokaryotes, it occurs in the cytoplasm. In eukaryotes, it initially occurs in the nucleus to create a transcript (mRNA) of the coding region of the DNA. The transcript leaves the nucleus and reaches the ribosomes for translation into a protein molecule with a specific sequence of amino acids. Protein synthesis (also called protein biosynthesis when performed by a living organism) is a process of creating protein molecules. In biological systems, it involves amino acid synthesis, transcription, and translation. In amino acid synthesis, there is a set of biochemical processes that produce amino acids from carbon sources like glucose. Not all amino acids are produced by the body; other amino acids are obtained from the diet.

Within the cells, proteins are produced by transcription and translation processes. (Ref. 8) Transcription is the process wherein the mRNA is transcribed from DNA to serve as a template for translation. Translation is the process wherein amino acids are linked together in a specific order according to the rules specified by the genetic code. It occurs in the cytoplasm where the ribosomes are located. The steps of translation are: (1) the binding of mRNA to a ribosome, (2) the ribosome begins matching tRNA anticodon sequences to the mRNA codon, (3) the amino acid carried by the tRNA gets added to the elongating chain, and (4) a stop codon is reached, releasing the polypeptide and the mRNA. The events that follow protein synthesis include proteolysis, post-translational modification, and protein folding. (Ref. 9) Proteins abound in any cell. A human cell may contain about 1 to 3 billion proteins. (Ref. 10) The number, though, may vary based on the cell’s activity.