The mechanism of protein biosynthesis in an organism of animals.
Protein biosynthesis is when biological cells generate new proteins; it is balanced by the loss of cellular proteins via degradation orexport. Translation, the assembly of proteins by ribosomes, is an essential part of the biosynthetic pathway, along with generation ofmessenger RNA (mRNA), aminoacylation of transfer RNA (tRNA), co-translational transport, and post-translational modification. Protein biosynthesis is strictly regulated at multiple steps, and error-checking mechanisms are in place.
Proteins are assembled from amino acids using information encoded in genes. Each protein has its own unique amino acid sequence that is specified by the nucleotide sequence of the gene encoding this protein. The genetic code is a set of three-nucleotide sets calledcodons and each three-nucleotide combination designates an amino acid, for example AUG (adenine-uracil-guanine) is the code for methionine. Because DNA contains four nucleotides, the total number of possible codons is 64; hence, there is some redundancy in the genetic code, with some amino acids specified by more than one codon.[6] Genes encoded in DNA are first transcribed into pre-messenger RNA (mRNA) by proteins such asRNA polymerase. Most organisms then process the pre-mRNA (also known as a primary transcript) using various forms of Post-transcriptional modification to form the mature mRNA, which is then used as a template for protein synthesis by the ribosome. In prokaryotes the mRNA may either be used as soon as it is produced, or be bound by a ribosome after having moved away from the nucleoid. In contrast, eukaryotes make mRNA in the cell nucleus and then translocate it across the nuclear membrane into the cytoplasm, where protein synthesis then takes place. The rate of protein synthesis is higher in prokaryotes than eukaryotes and can reach up to 20 amino acids per second.
87.Stages of protein translation: initiation, elongation and termination. Terminal codons.
Translation consists of 3 steps: initiation, elongation, and termination.
Translation: Initiation
The mRNA molecule to be decoded binds to one subunit of the ribosome, then the other ribosomal subunit binds to both of those. In the process, a tRNA with the amino acid methionine attached docks in the ribosome's P site.
Translation: Elongation
The following cycle is repeated again and again, elongating the polypeptide by 1 amino acid per cycle.
(1) a charged tRNA docks in the A site and the existing, growing polypeptide is transferred from the tRNA molecule in the P site to the new tRNA's amino acid.
(2) translocation: The ribosome moves 3 bases along the mRNA, moving the uncharged tRNA in the P site into the E (exit) site, the tRNA in the A site (with the polypeptide now attached) into the P site, and positioning a new codon into association with the now-empty A site.
(3) Back to step (1)
Translation: Termination
Eventually, translocation brings a stop codon into the position associated with the empty A site. A stop codon does not code for an amino acid, but for a release factor. The release factor binds and then frees the polypeptide and dissociates the ribosome.
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Terminal codon is the codon which is the last codon of the strand. It is actually a STOP CODON- UGA, UAA, UAG which is involved in the termination of protein synthesis. Termination of protein synthesis follows 2 mechanisms - RHO DEPENDENT MECHANISM: which depends on the protein rho and RHO INDEPENDENT MECHANISM: independent of rho factor.
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