It is the step of the protein-synthesis pathway that is responsible for the expansion of nascent polypeptide chains which is known as the elongation. Two-site model: The two-site model proposes that the ribosome has two sites for transfer RNA (tRNA) binding, one of which binds aminoacyl-tRNAs preferentially and another which binds peptidyl-tRNAs exclusively. The findings of the study of the effects of tRNA and elongation factor binding on the reactivity of ribosomal RNA bases have led to the development of the hybrid-sites model, which is based on these findings. The changes in 16-S rRNA reactivity observed when tRNAs bind to ribosomes are wholly dependent on interactions involving the anticodon stem/loop of tRNA; the changes in 23-S rRNA reactivity observed are solely dependent on interactions involving the CCA end of tRNA. It is the most abundant protein in bacterial cells, known as the elongation factor Tu (EF-Tu). There are around 10 copies of EF-Tu per ribosome, which is approximately the same amount as there is aminoacyl-tRNA, and the majority of EF-Tu in the cell is found complexed with aminoacyl-tRNA. Additionally, the complexation of aminoacyl-tRNA with EF-Tu protects it against deacylation, which occurs when aminoacyl-tRNA is delivered to ribosomes that have been programmed by messenger RNA (mRNA)
Elongation in plant
The term “elongation” will be used to refer to any permanent expansion of cells that have already been produced by differentiation. Because the extent of the surface of a plant cell’s wall determines the size of the cell, cell elongation can be defined as any permanent increase in the surface of the cell wall.
Auxin is a plant hormone that is produced at the tip of the stem and is responsible for cell elongation. Auxin goes to the darker side of the plant, causing the cells on that side of the plant to grow larger than the corresponding cells on the lighter side of the plant, leading the plant to grow larger overall.
The bulk of cell elongation happens after the completion of cell division, which means that the actions of cell proliferation factors and cell expansion factors are separated in time, as previously stated. In addition, some signals, such as auxin, can regulate both cell proliferation and cell elongation.
The first round of elongation
Immediately after the formation of the initiation complex, but before any amino acids have been joined together to form a chain.
The P site of the ribosome is where our first tRNA, which carries the amino acid methionine, begins its journey through the ribosome. A new codon is exposed in another slot, which is referred to as the A site, just next to it. The A site will serve as the “landing point” for the next tRNA, which will be one whose anticodon is a perfect (complementary) match for the codon that was exposed earlier in the process.
Once the appropriate tRNA has been recognised in the A site, it is time to get to work on the action: the production of the peptide bond that joins one amino acid to another. This step involves the transfer of methionine from the first tRNA to the amino acid of the second tRNA located in the A site of the second tRNA.
Not bad—we now have two amino acids and a polypeptide (albeit a very small one)! The methionine is located at the N-terminus of the polypeptide, whereas the other amino acid is located at the C-terminus of the polypeptide.
However, the chances are that we will require a polypeptide that is longer than two amino acids. How does the chain of events continue to expand? A single codon in the mRNA is used to pull the mRNA onward via the ribosome once the peptide bond has been created. Due to this change, the first, empty tRNA can drift out through the E (“exit”) site. It also exposes a new codon in the A site, allowing the entire cycle to be repeated once more.
Termination
Polypeptides, like all good things, must come to an end at some point in time. Termination is the process by which translation comes to an end. When a stop codon (UAA, UAG, or UGA) in the mRNA enters the A site, the process is known as a termination.
Stop codons are detected by proteins known as release factors, which are small proteins that fit nicely into the P site (even though they are not tRNAs). Release factors interfere with the enzyme that is ordinarily responsible for forming peptide bonds by causing it to add a water molecule to the last amino acid in the chain, which is undesirable. When the chain is separated from the tRNA, the newly formed protein is discharged into the environment.
Conclusion
Cell enlargement and the production of new cell walls take place in the cells that are present during the elongation phase. Cellular modifications, such as the formation of bigger vacuoles, take place here. In higher plants, the ability to exhibit high levels of developmental plasticity is dependent on the coordination of cell elongation by a variety of hormonal and environmental signals. These signals include, in particular, light, temperature, auxin, gibberellin (GA), and brassinosteroid (BR), all of which have significant effects on cell elongation and seedling development.