In this video, we're going to talk more details about the ribosome, specifically the ribosomal tRNA binding sites. And we'll talk about an overview of translation as well. Now keep in mind that this video is really just the introduction and the overview of the ribosomal tRNA binding sites and this process of translation. But as we move forward in our course, we're going to break down the process of translation into its steps. And so we're going to talk more details about translation as we move forward in our course, and this video here is really just the overview. So keep that in mind as we move forward through this video.

Each of the ribosomes is going to have 3 tRNA binding sites. Recall that the tRNAs are the transfer RNAs that are going to be attached to amino acids and bring amino acids to the ribosome. The tRNA binding sites are found within the ribosome, and there are 3 tRNA binding sites. The first tRNA binding site is going to be the aminoacyl tRNA binding site, otherwise just abbreviated as the A site. The A site is where the tRNAs originally enter into the ribosome. It holds the tRNA that's carrying the next amino acid to be added. tRNAs will enter into the ribosome through the A site.

As shown in the image, this represents the mRNA, our messenger RNA. The ribosome receives tRNAs like this one right here; this box represents the tRNA. Since it's attached to an amino acid, this little purple circle represents an amino acid. That makes this tRNA a charged tRNA. Again, the charge has nothing to do with the positive or negative electrical charge. Instead, the charged tRNAs are attached to amino acids. Amino, tRNAs, charged tRNAs originally enter into the ribosome into the A site. The first site here is the A site.

The second ribosomal tRNA binding site is the P site or the peptidyl tRNA binding site, otherwise known as the P site. The P site holds the tRNA that's carrying the growing polypeptide chain or the growing protein chain. The image shows the P site in the middle holding the tRNA attached to this growing polypeptide chain. The P site contains the tRNA bound to the growing polypeptide chain. Notice that the tRNA has the anticodon, and the anticodon pairs with the codon of the mRNA. We'll talk more details about this process as we move forward in our course.

The third and final site of the tRNA, the ribosome tRNA binding site is the E site or the exit site. The E site, of course, is where the discharged tRNAs leave the ribosome from this site. The E site is on this end of the ribosome. The discharged tRNAs, which again have nothing to do with the electrical charge, are not attached to an amino acid because the amino acid was transferred over to this growing chain, this growing polypeptide chain. The discharged tRNAs without the amino acid exit the ribosome through the E site.

Here is what we are seeing: charged tRNAs bring amino acids to the ribosome and enter into the A site. Then the P site contains the growing polypeptide chain where the amino acid is added to the growing polypeptide chain. The ribosome continues to shift along the mRNA; the tRNAs in the P site shift into the E site and then eventually exit the ribosome in this way. Essentially, charged tRNAs come in, they make their way from the A site to the P site to the E site, and then ultimately leave the ribosome. This is a very detailed and complex process that involves a lot of moving pieces. This here is really just the introduction to these three ribosomal tRNA binding sites, and we're going to talk more details in a step-by-step manner of the process of translation involving all of this as we move forward in our course. But for now, this here concludes our overview of the tRNA binding sites, and we'll be able to get some practice applying these concepts as we move forward. So, I'll see you all in our next video.