In this video, we're going to talk about the second step of translation, which is the elongation of translation. And so of course, elongation just means making something longer. And what's going to be made longer is the growing polypeptide chain, the growing amino acid chain. During the elongation of translation, amino acids are going to be added one by one to the previous amino acid at the C terminus of the growing chain. Therefore, this means that the polypeptide chain is going to be growing from its N terminus to its C terminus. Now, the ribosome, again, is going to be the main structure involved with translation, and it's going to be reading the mRNA, the messenger RNA, in codons. It's going to be reading the mRNA codons from the 5' end of the mRNA to the 3' end of the mRNA. As it reads these codons, these three nucleotide sequences, the ribosome is going to be pairing each of the mRNA codons with the correct respective tRNA anticodons. And those tRNAs, we know, are going to be specifying one amino acid. And so each codon will specify one amino acid by pairing with a tRNA that is attached to that amino acid.
Now the way that translation elongation works is that new tRNAs that are charged and attached to amino acids are going to enter the ribosome's A-site and then shift into the ribosome's P-site. And then finally, they're going to exit the ribosome through the ribosome's E-site before exiting. And so if we take a look at our image down below at the elongation of translation, we can better understand how this process works. At the very beginning, what we're showing you is the end result of the initiation of translation, where we have the small and large ribosomal subunit are intact and bound to the very first tRNA, and the messenger RNA, the mRNA. And so what you can see here is that charged tRNAs, or tRNAs that are attached to amino acids, are going to enter into the ribosome into the ribosome's A-site. So that's what we have here as the very first step, that charged tRNAs are going to enter into the ribosome via the A-site. And then, what's going to happen is, a peptide bond is going to be formed. And recall that a peptide bond is a covalent bond between amino acids.
What happens here is that the first amino acid, in this position, is going to be covalently linked to the next amino acid. And so, it gets passed on to this tRNA here. And so you can see they've been covalently linked, these two amino acids. We have a growing amino acid chain here. Now, what happens is, the ribosome is going to continue to shift along the mRNA, and that causes the discharged tRNA. Remember, discharged tRNAs are tRNAs that are not attached to amino acids because, again, its amino acid was linked to the previous amino acid. And so the discharged tRNA is going to enter and exit, enter the E-site and exit the ribosome through the E-site. And so you can see here that the discharged tRNA is exiting through the E-site. And meanwhile, the other tRNA is shifting into the P-site. The tRNA is going to shift into the P-site. And ultimately, the process would just continuously repeat over and over again to continuously add amino acids and grow this polypeptide chain. And so that is going to be the elongation of translation, and we'll be able to talk about the final step of translation, the termination of translation in our next video. So I'll see you all there.