Elongation

Multiple physiological functions are served by halting the RNA polymerase during transcription elongation. Because of the sequence variability of the DNA being transcribed, as well as specific interactions between polymerase and particular DNA sequences, the pause mechanism is dependent on these factors.

For example, elongation occurs during translation, a stage in protein biosynthesis in which the genetic code carried by mRNA is decoded to produce the specific sequence of amino acids in a polypeptide chain. The translation is one example of a step in which elongation occurs. Translating mRNA occurs once an activating factor binds to the 5′ end of mRNA, which signals the ribosome to begin the process of translation. The initiation phase is the first stage in the process. The elongation stage is performed after this step. The next aminoacyl-tRNA in line binds to the ribosome, along with GTP and an elongation factor, at which point the ribosome elongates. This is followed by termination, which occurs when the A site of the ribosome comes into contact with a stop codon. The elongation phase is also included in the gene transcription procedure.

Initiation

The transcription process necessitates a partial unwinding of the DNA double helix at the area of mRNA production. A transcription bubble is a term used to describe the region of unwinding. A promoter is a DNA sequence that serves as a binding site for the proteins and enzymes that are involved in transcription, allowing the process to begin. The majority of the time, promoters are found upstream of the genes that they regulate. The exact sequence of a promoter is extremely essential because it controls whether or not the related gene is transcribed all of the time, some of the time, or rarely at all.

Elongation

Both the P and A sites on the ribosome are involved in tRNA binding; the P site is responsible for holding the peptide chain, and the A site is responsible for accepting the tRNA.

In contrast to Methionine-tRNA, the aminoacyl-tRNA that is complementary to the following codon attaches to the A site, utilising the energy released by GTP hydrolysis to do this.

Methionine transfers from the P site to the A site to form a bond with a new amino acid at the A site, so kicking off the expansion of the peptide chain. The tRNA molecule in the P site no longer has an amino acid connected to it, and as a result, it exits the ribosome.

It then translocates along the mRNA molecule to the next codon, utilising the energy released by GTP hydrolysis to do it once more. The expanding peptide is now located at the P site, and the A site is ready to accept the binding of the next aminoacyl-tRNA, allowing the cycle to repeat itself. It is necessary to build up the polypeptide chain in the direction from the N terminal (methionine) to the C terminal (the final amino acid).

Termination

It is necessary to instruct the bacterial polymerase to separate from the DNA template and release the freshly created mRNA when a gene has been successfully transcribed. There are two types of termination signals, depending on the gene that is being transcribed; nevertheless, both use repeated nucleotide sequences in the DNA template that cause RNA polymerase to stall, allowing the DNA template to be released and the mRNA transcript to be released.

The process of transcription is complete when the programme is terminated. The transcript in a prokaryotic cell would have already been utilised to partially synthesise numerous copies of the encoded protein by the time termination occurs since these processes can occur concurrently using multiple ribosomes in prokaryotic cells (polyribosomes)

Processing of RNA in Eukaryotes

Before they can be transported from the nucleus to the cytoplasm and translated into proteins, newly transcribed eukaryotic mRNAs must go through a series of processing stages. A molecule that is far more stable than a prokaryotic mRNA is created by the additional stages needed in eukaryotic mRNA maturation, which are not present in prokaryotic mRNA. The average bacterial RNA is only good for five seconds, whereas eukaryotic mRNAs are good for several hours or even days.

Conclusion

It is important to note that elongation is a dynamic process that changes depending on how heterogeneous the DNA being transcribed is in terms of the sequence. As a result, it should come as no surprise that the composition of the elongation complex changes as a gene is transcribed.

The transcription elongation process is controlled by stopping RNA polymerase in several instances during the transcription process. These pauses are required in bacteria because the transcription of DNA into mRNA and the translation of that mRNA into a protein are both linked. In eukaryotes, on the other hand, transcription is closely associated with mRNA processing. Because of this, pausing RNA polymerase around exon-intron junctions is required to improve the efficiency of mRNA splicing.