What is Protein Biosynthesis?
Protein biosynthesis is a biochemical process that allows synthesis of proteins from simple amino acids. The process takes several steps with the aid of information from the DNA. It is an important process in human beings because it helps cells to build proteins. While the term sometimes denotes protein translation, it goes through multiple steps, starting with synthesis of amino acids and transcription, which are essential during translation stage. Even though they are similar, this process differs widely from prokaryotes and eukaryotes. Events that come after this biosynthesis are post-translational modification and protein folding. During and after the process, polypeptide chains fold to assume native secondary and tertiary structures through protein folding.
The Four Steps of Protein Biosynthesis
Synthesis of proteins into amino acids does not occur in a single step. Normally, this process goes through four steps, which include activation of amino acids, initiation of chain formation, chain elongation and chain termination. In the following sections, we shall discuss the four steps of protein biosynthesis in details.
Step 1: Activation of amino acids – during this process, aminoacyl-tRNA forms. It is at this stage that the activation of the 20 amino acids takes place through esterification with a specific t RNA. The process takes place in the cytoplasm and is enabled by aminoacyl-tRNA synthetases. These are a group of enzymes, which are specific to a particular amino acid. For the process to take off and run to completion, activation energy is required. This is supplied through ATP consumption. Before this process begins, all component elements are gathered in the ribosome.
Step 2: Chain formation stage. Here, chain formation and attachment to ribosome subunits takes place. At this point, the first aminoacyl-tRNS starts the process in the form of an N-Acyl derivative. This is necessary to ensure that polypeptide chain synthesis begins at the beginning of the genetic message. The AUG codon on mRNA initiates protein synthesis in the cytoplasm. The AUG codon triggers the interaction of ribosome with m-RNA plus the tRNA with anticodons (UAC).
The tRNA that initiates the process of protein synthesis has N-formyl-methionine attached. Since the formyl group is formic acid, it is converted into an amide. This convertion is made possible because of the -NH2 group that occurs on methionine. After this, the second tRNA approaches the codon-CCG or as mRNA, the code for proline. The anticodon, which helps to decode this, is GGC. The final stage is the growth of the peptide chain, as the amine of proline bonds to the carboxylic acid group of methinone.
Chain elongation in protein conversion
The third process during protein biosynthesis if chin elongation. The peptide grows into an elongated chain because of the nonstop attachment of amino acyl residues. Aminoacyl-tRNA esters are responsible for the translation of the residues and are determined by a codon that occurs in the mRNA. MRNA and the peptidyl-tRNA chain move along the ribosome once each peptide attaches. This allows proper positioning of the next codon. In this stage, GTP consumption supplies the necessary reactive energy.
Chain termination Stage: Protein Biosynthesis
The last stage for the process is chain termination. This is also accompanied by the release of the ribosome. For the termination to take place, adequate termination signals must be present in the mRNA. In the end, the completed chain detaches from the ribosome. The process of releasing the polypeptide-tRNA starts after reaching the stop codon by particular release factor that attaches to the ribosome. At this point, it cleaves the ester bond hydrolytically between polypeptide and tRNS.
Here, the 70S-ribosome is ready to leave the mRNA in a free state, after which it can join a new cycle through dissociation of the subunits, i.e. 50S and 30S. During elongation and termination of the chain, the last amino acid is hydrolyzed from tRNA. The process can repeat several times as long as a protein factor is present. Thus, protein biosynthesis happens if the four stages take place successfully. The process is crucial because if forms the basis of building cells in human boy. However, the right parts and conditions for every step must be met for the process to run to completion.
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References:
http://chemed.chem.purdue.edu/genchem/topicreview/bp/1biochem/synthesis9.html
http://chemistry.elmhurst.edu/vchembook/584proteinsyn.html
http://flexikon.doccheck.com/en/Protein_biosynthesis
http://themedicalbiochemistrypage.org/protein-synthesis.php
http://www.proteinsynthesis.org/what-is-protein-synthesis/
http://www.sciencedaily.com/terms/protein_biosynthesis.htm