Charging of tRNA

00:01 Now that you have a great understanding of transcription, it’s time to come on and look at the details of translation.

00:08 Now we’re moving from messenger RNA to the polypeptide itself.

00:12 And we’re switching languages.

00:14 So we’re taking the ingredients on our printed copy and we’re making our final dish, the polypeptide.

00:22 So by the end of this lecture, you will be able to explain the tRNA charging process as well as diagram ribosomal anatomy and describe what happens during the initiation, elongation, and termination phases.

00:38 We will also be able to distinguish the difference in bound and free ribosomes during translation process.

00:46 So let’s get started.

00:48 Looking at tRNAs.

00:50 There are a lot of different ways for us to depict a translational RNA.

00:55 Three-dimensional models, whatever.

00:57 Most of the time, we will end up using the icon on the right hand side to represent tRNA.

01:03 Either way, all of our tRNAs will have an amino acid accepting end as well as an anticodon end, which is on the loop of RNA and will pair with the codons on messenger RNA.

01:19 So now that we have an understanding of the basic anatomy of a tRNA, let’s look at how we get them charged.

01:26 That is how do we get them associated with the appropriate amino acids so that they can go to the ribosome and do their job.

01:35 So here, we have an aminoacyl-tRNA synthetase, that is my favorite enzyme to say.

01:42 And it has a binding site for the tRNA.

01:46 Now, each tRNA will have a specific binding site on a specific tRNA synthetase.

01:55 And it will have an amino acid binding site that’s specific to the amino acid that needs to matched to that tRNA.

02:04 It requires a little bit of energy to charge it.

02:07 And so we apply some ATP, which is cleaved, leaving AMP behind and will take a tRNA that’s specific to that tRNA synthetase and put it into the binding site.

02:20 The anticodon on that tRNA will pair with tRNA codons essentially inside the tRNA synthetase, that’s how they recognize each other and then we’ll pair the amino acid with the tRNA.

02:35 We lose the AMP and then we can release the tRNA that is now charged, has its specific amino acid.

02:45 It’s ready to go to the ribosome and do its duties there.

02:49 So now we know how we charged our tRNA synthetases.

02:53 It’s important to recognize that there are multiple different tRNA synthetases, and that it varies how many there are from species to species.

03:04 We should have at least 20 of them because there are 20 different amino acids and we need to bind to specific amino acid to a tRNA.

03:13 But as we’ll see later, we can have a little bit of wobble in the pairing of the anticodon.

03:19 You’ll recall when we learned about the genetic code, there are some codons or some amino acids in which there are several different ways to code for them on messenger RNA.

03:32 So we’ll look at that towards the end of this lecture.