 Do you see why I gave us some time to think about tRNA molecules and ribosomes before showing you this diagram? Let's orient ourselves. Diagrams, especially scientific diagrams, they're often profoundly complicated, and they contain gobs and gobs of information. Let's see the things that we know or the things that we recognize. I recognize these guys. Look, they've drawn tRNA molecules with attached amino acids. So what we know, because we are experts, we know that this is the anticodon. We know that that's the amino acid associated with that anticodon. Here's another one out here in the world. Here's another full tRNA molecule. I just want to point to the fact that there are tRNA molecules out there that aren't full. Notice this tRNA molecule off to the left. That guy doesn't have an amino acid anymore. We will see why, where its amino acid actually went, but it's now an empty tRNA molecule. What's it going to do? Empty tRNA molecules get released back into the cytoplasm, and as soon as they come across their amino acid, they're no longer going to be empty, because that amino acid binding site is just going to stick to their amino acid. It's super easy. Do you see, we had our sites, they sort of diminished our sites. Remember how we had the E, P, and A sites? Let's go ahead and just make sure that we've got those labeled here. We do, this is the exit site. This is the peptide where we have the growing peptide, and this is the arrival site, or the amino acid site. And check it out. We have the arrival of an amino acid. We have a growing polypeptide, which is just a string of amino acids. The string of amino acids is held on that center in that P site. That string of amino acids is held there. Here's what's interesting. The messenger RNA molecule, which attached, is being read, you can see that the ribosome is moving that direction, which means you can imagine the ribosome moving down the strand of messenger RNA, such that this is my next codon that's going to be read. And it's almost ready to read the next codon. This amino, I mean, tRNA molecule in the E site has to leave. So it bounces off. You can see that arrow right here. The protein chain, that peptide chain, this is the work of the ribosome. Whoa. No, no, no, sorry. The work of the ribosome is to take this growing polypeptide and transfer it to the amino acid that is on the tRNA that just arrived in the A site. Do you follow that? I'm going to do an animation of this in the next video, and not having a moving picture is difficult. But imagine that this whole string of peptides gets attached to the new amino acid that just arrived at the A site. Now the tRNA in the P site is empty, and the tRNA in the A site is full of a peptide. So the whole thing shifts. The empty tRNA has to move to the E site. The peptide carrying tRNA moves to the P site, and somebody new comes in, arrives to the A site, and we're back to this beginning point again. This continues all the way until we hit the stop message. If you look at our genetic code, there's actually a codon that says stop. I always get nervous because I always forget to check for my stop codons, and in quizzes or examples, sometimes I'll put a stop codon in the middle of a sequence, and there is no amino acid that gets added at a stop codon. So a tRNA, there's no tRNA, there's a tRNA that has the anti-codon that matches these stop codons doesn't have an amino acid attached, which the ribosome reads that and goes, oh, there's nothing more to add, and the whole thing continues, and the protein falls off, literally falls off of the ribosome. This finished protein, because we hit the stop codon. Imagine a stop codon mutation, where instead of coding for tyrosine, you code for stop. That's going to be a big deal. That's going to be a mutation that is probably going to have an impact of some sort on the critters function. Okay, I think that we're ready to actually walk through and visualize this process. See all of it in rig style animation. Be right back.