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 going to be 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 the aminoacyl tRNA binding site, otherwise just abbreviated as the A site.

The A site is going to be the site 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. If we take a look at our image down below, you'll notice we've got our ribosome, our complete intact ribosome here in the background. The complete intact ribosome is going to be bound to our mRNA.

This right here represents our mRNA, our messenger RNA. What this ribosome does is it will receive tRNAs like this one right here. This box here represents the tRNA. And because it's attached to an amino acid, this little purple circle here represents an amino acid, that makes this tRNA a charged tRNA. The charge has nothing to do with the positive or negative electrical charge but instead indicates that tRNAs are attached to amino acids. Charged tRNAs originally enter into the ribosome into the A site. You can see the first site here is the A site. Now the second ribosomal tRNA binding site is going to be the P site or the peptidyl tRNA binding site, otherwise known as the P site.

The P site is going to be the site that is going to be holding the tRNA that's carrying the growing polypeptide chain or the growing protein chain. If we take a look at our image down below, what you'll notice is the P site is here in the middle, and the P site is going to be holding the tRNA that is attached to this growing polypeptide chain here. So, this background right here represents the growing polypeptide chain. The P site will have the amino acid attached tRNA, that is bound to the growing polypeptide chain. Notice that the tRNA is going to have the anticodon and the anticodon is going to pair with the codon of the mRNA. This will be a process that we'll talk more details about as we move forward in our course.

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

What we're seeing here is that charged tRNAs are bringing amino acids to the ribosome and they're entering into the A site. Then the P site is going to contain the growing polypeptide chain where the amino acid is just going to be added to the growing polypeptide chain. Then, the ribosome is just going to continue to shift along the mRNA and what happens is that the tRNAs in the P site will shift into the E site and then eventually exit the ribosome in this way. So basically, what's happening is 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. Again, 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.