Translation elongation phase

Inhibition of protein synthesis in eukaryotic cells by the Cephalotaxus alkaloids harringtonine, homoharringtonine, and isoharringtonine has been studied.16 In model systems, these alkaloids were found not to inhibit any of the initiation steps but to block certain parts of the elongation phase of translation. 

When the 70S initiation complex has been formed, the ribosome is ready for the elongation phase of protein synthesis. The fMet-tRNAf molecule occupies the P site on the ribosome. The other two sites for tRNA molecules, the A site and the E site, are empty. Formylmethionyl-tRNAf is positioned so that its anticodon pairs with the initiating AUG (or GUG) codon on mRNA. This interaction sets the reading frame for the translation of the entire mRNA. 

During translation, the ribosome binds to the mRNA at the start codon (A UG) that is recognized only by the initiator tRNA. The ribosome proceeds to the elongation phase of protein synthesis. During this stage, complexes, composed of an amino acid linked to tRNA, sequentially bind to the appropriate codon in mRNA by forming complementary base pairs with the tRNA anticodon. The ribosome moves from codon to codon along the mRNA. Amino acids are added one by one, translated into poly-peptidic sequences dictated by DNA and represented by mRNA. 

Translation begins with the binding of the ribosome to mRNA. A number of protein factors transiently associate with the ribosome during different phases of translation Initiation factors, elongation factors, and termination factors. 

During translation the mRNA is read in a 5 to 3 direction and protein is made in an N-terminal to C-terminal direction. Translation relies upon aminoacyl-tRNAs that carry specific amino acids and recognize the corresponding codons in mRNA by anticodon-codon base-pairing. Translation takes place in three phases initiation, elongation and termination. 

No matter what the organism, translation consists of three phases initiation, elongation, and termination. The elongation reactions, which include peptide bond formation and translocation, are repeated many times until a stop codon is reached. Posttranslational reactions and targeting processes vary according to cell type. 

In addition to the ribosomal subunits, mRNA, and aminoacyl-tRNAs, translation requires an energy source (GTP) and a wide variety of protein factors. These factors perform several roles. Some have catalytic functions others stabilize specific structures that form during translation. Translation factors are classified according to the phase of the translation process that they affect, that is, initiation, elongation, or termination. The major differences between prokaryotic and eukaryotic translation appear to be due largely to the identity and functioning of these protein factors. 

The predominant conformation of the mother compound bicyclo[3.3.1]nonane in the gas phase is the double chair (cc), as detected by electron diffraction studies (120-123). The most important destabilization in the cc conformer of this structure is van der Waals repulsion of the endo-3- and endo-7- hydrogen atoms. In the twin-chair conformation with ideal tetrahedral angles, the C3-C7 separation would be 2.5 A and the separation of the corresponding endo-hydrogen atoms would have the physically impossible value of 0.75 A (124). Repulsion induces an elongation of the C3- - C7 distance to 3.1 A, which translates to an endo-hydrogen distance of 2.2 A,... 

The GTP carried by IF2 is hydrolyzed, and IF2-GDP, Pi, and IFl are all released. The VOS initiation complex is ready to accept a second charged tRNA and begin elongation, the next phase of translation. 

The structure changes of metallic (5, 5) carbon nanotube at its expansion are calculated by the molecular orbital method. It is found that the ground state of the non-expanded nanotube is dielectric (phase A) as a result of Peierls distortions. The phase A has the Kekule structure with a triple translation period in comparison with the metallic phase (phase C). Two structural first order phase transitions are revealed. The transition between the phase A and intermediate phase B takes place at the elongation of 5 %. The transition between the phases B and C takes place at the elongation of 13 %. The metastable states are found for the phases A and B. 

Translation converts the genetic information embodied in the base sequence (codon) of mRNA into the amino acid sequence of a polypeptide chain on ribosomes. Protein biosynthesis (Amstein and Cox, 1992 Lee and Lorsch, 2(X)4 Moldave, 1981) begins with the activated amino acids (aminoacyl-tRNA) and is characterized by three distinct phases initiation, elongation and termination. 

The activity of a target gene product can also be modulated at the post-transcriptional level by adjusting the efficiency at which mRNA is translated into a polypeptide chain. Translation is conceptually divided into four phases initiation, elongation, termination, and ribosome recycling [163]. Regulation of... 

The large (50s) subunit contains 23s rRNA, 5s rRNA, and over 30 proteins, and the small (30s) subunit contains 16s rRNA and about 20 proteins. The complete 70s ribosome is formed by association of the 30s and 50s subunits through a networks of bridges. The 30s subunit mediates the interaction between mRNA codons and tRNA anticodons on which the fidelity of protein translation depends. The 50s subimit includes the activity that catalyzes peptide bond formation—peptide transferase and the binding site for GTP— which are the binding protein factors that assist in the initiative elongation and termination phases of protein synthesis. 

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