Hi. In this video, we're going to be talking about RNA translation. So first, we're going to give just a brief overview of translation. A lot of this is probably going to be familiar, but I might be introducing a few new concepts, before we get into really the nitty-gritty details of how translation happens. So, the first thing is translation is the process of changing an mRNA transcript to a protein. The main driver of this is the ribosome. It really drives translation. And, as we've discussed before, it consists of two subunits, small and large, which are made up of a combination of RNA and protein. RNA actually makes up the majority of the ribosome, approximately two-thirds, and is responsible for a lot of its enzymatic properties. So, the ribosome affects translation because it binds to tRNAs in three different locations. Remember tRNA sort of adapts between the RNA and the ribosome because they actually are the ones that carry the amino acids that form the protein. Now, these three locations are called the A, P, and E sites, and they all have fancy little names here, but generally, you just need to know APE or APE. The A site is where the tRNA recognizes the codon. The P site is where the amino acid is actually linked to the polypeptide chain, and the E site is the exit site, so it leaves. It exits the ribosome. Now, to initiate, there's a special initiator tRNA that initiates translation. This is bound to both the start codon and the amino acid, a really special methionine, which acts as the initiator amino acid to start protein synthesis. So, in prokaryotes, this is bound to a really special methionine called formylmethionine. But again, we don't really focus a lot on prokaryotes, but I do want to mention it here just because there are some differences. And the start codon here is AUG. So, if we were to look at what this looks like, let me back out here. Title is overview of ribosomal sites and mRNA translation. But you can see here that there is an A site, a P site, and there's also an E site of it exiting here. E, really for exiting. And so, what happens is you have your tRNA bound to amino acids, and it comes in, and in the A site it recognizes the nucleotides. In the P site, it adds an amino acid to the polypeptide chain, and in the E site it exits. So that's kind of the overview of translation. Let's now turn the page.
Translation: Videos & Practice Problems
Translation is the process of converting mRNA into proteins, primarily driven by ribosomes, which consist of a small and large subunit. The ribosome has three sites: the A site (aminoacyl site), P site (peptidyl site), and E site (exit site). Initiation begins with the binding of initiator tRNA to the P site, followed by scanning for the start codon (AUG). Elongation involves the addition of amino acids to the growing polypeptide chain, while termination occurs at stop codons, facilitated by release factors. Prokaryotic translation differs by using the Shine-Dalgarno sequence for ribosome binding.
Translation Overview
Video transcript
Translation Steps
Video transcript
Okay. So, you will notice that this is another video about steps. There are a lot of steps in cell biology, and we're just going to have to get through them. So, let me disappear. It's really complicated, but I'm going to walk it through, walk this through, slowly. I'm going to disappear so you make sure you can see everything and I'm not standing in the way. So, the very first step to translation is that the tRNA binds to the small subunit of the ribosome and other translation initiation factors. So, it is not just the ribosome, there are all these other proteins, which you will see in your textbook called IFs and EIFs. And these translation initiating factors are also important for translation. And so, it's important here to know that this first tRNA site binds to the P site, which you remember is kind of the second site, and only the initiator tRNA can bind here, and only when the large subunit isn't attached. So this very first step is a really unique thing, where the initiator tRNA binds to the P site, which is kind of weird. And that only happens before it interacts with any kind of RNA or even the large subunit. And so, once the initiator tRNA is bound to the small subunit of the ribosome, it can bind the 5′ prime end of the mRNA transcript, where it then scans until it reaches AUG. So if we are going to look at this what we are going to see is you are going to have your small subunit and your initiator tRNA and this is your methionine, amino acid, and they bind together. So this is really step 1. And here are some other factors here, these EIF, IF, here is another one, EIF 4. Now, step 2 is they are recruited to this 5′ prime end, and then they move along here until they find the start sequence. So, if you can see that, it is actually AUG. So this is the start codon for translation. Now, when it gets to the AUG site, what happens is it stops, and the large subunit is recruited to the site. And so you can see here, and then all of these different factors leave. So you can see here that it stopped here on this AU AUG site, this large subunit comes in, binds, forms this ribosomal complex, and all the other factors leave. It goes somewhere else. So, now, we're on step 4. What happens at step 4 is, it starts going through the different sites. So, the amino acid is cleaved from the initiator tRNA, which is in the P site, and so that forms the very first amino acid. And then, more tRNA is continually brought to the A site. And so, you can see this here, this image. You have, your initiator tRNA, the large subunits coming in, being recruited. And recruited. And, eventually, this amino acid goes up to start forming the peptide chain, where other tRNAs are continually brought in. So this is repeated over and over again, you're about to see. So this is repeated over and over again, you're about to see, to form the whole polypeptide chain. But it's important to realize that there's a large subunit and a small subunit of the ribosome, and each of them has different functions. So, the large subunit is actually responsible for binding the amino acids together, and the small subunit is responsible for matching tRNA's to mRNA codons. So that's just sort of you know, which subunit is doing what. Now, as these, let me scroll down here. As these amino acids continually linked together, you see, you get forming these, polypeptide chains. And so, once the amino acid is added, the ribosome moves 3 nucleotides, 1 codon at a time, and the tRNA moves down the site. So you can see here it starts here, it enters here, and see, yeah, enters here. Oh, you can't see that cause it's green. It enters here. I can't really see any of these. It enters here at the A site, and then it moves to the P site. Remember, the A site, it recognizes the codon, and the P site, it adds amino acids. And so, every time it's added, another tRNA comes in and it's all replaced, and one exits and it's all moving 3 nucleotides at a time, sort of the ribosomes chugging along 3 nucleotides at a time. And so, there are, you know, of course, other proteins called elongation factors that come in and assist in this translation elongation. It can require energy, using GTP hydrolysis. One that you might read about in your textbook often is called EF 2. And this really helps tRNAs to bind to mRNAs and prokaryotes. And so these are just factors that really help the ribosome keep chugging, keep matching tRNAs and codons. But, eventually, the tRNA exits the ribosome, and the process continues, continually 5′ to 3′ prime until it reaches the end. Now, for termination, translation is terminated here when it reaches the stop codon. Here are the 3 ones here. And when it reaches here, what happens is there are these things called release factors that come, they hydrolyze or break apart a water molecule, and that releases the protein and the ribosome from the mRNA, and that can be started again. So what you see in this image, you finally reached a stop codon. Here it is. It reaches a, a release factor comes in that breaks apart water. And when it breaks apart, it releases energy and releases the ribosomes off of the mRNA, and this can start again. So these steps, are really long, really complicated, involve a lot of factors. Feel free to watch this video as many times as you need to kind of get down, you know, what these steps are and how they work and anything you might be confused about. But, overall, these steps occur really quickly, and they can require lots of ribosomes. So mammals have 10,000,000 ribosomes, 25% of E. Coli weight is just from ribosomes. So, translation is really important. It's really complicated, and it occurs really quickly. So now, let's move o
Prokaryotic Translation
Video transcript
Okay. In this video, we're going to be talking about prokaryotic translation. Translation in prokaryotic cells is different because, in eukaryotic cells, the ribosome depends on having a 5 prime cap on the transcript. But prokaryotes don't have that, so they have to have a different way for the ribosome to bind. How it does this is through the Shine-Dalgarno sequence, and this is where the prokaryotic ribosomes bind. Just a thing to know, other than the Shine-Dalgarno sequence, is that the prokaryotic ribosome is slightly smaller than the eukaryotic ribosome, and antibiotics generally work by targeting prokaryotic ribosomes while leaving the eukaryotic ribosomes alone. If we are just going to look at a brief sequence here, here is an mRNA sequence of a prokaryote. Here you have your Shine-Dalgarno sequence. The ribosome comes in, binds here, and then can translate this RNA into protein in prokaryotic cells. Like I said, this is going to be short, but just a general overview of prokaryotic translation. So let's move on.
Polyribosomes
Video transcript
Hi. In this video, we're going to talk about polyribosomes. So, what are polyribosomes? They are just a bunch of ribosomes that accumulate on a single transcript so that multiple RNA copies can be translated at the same time. So, it's really efficient. It saves time, and each ribosome or the next ribosome can begin when the preceding one has translated about 80 nucleotides. So, if we're just going to look at what this looks like, we can see here that we have our mRNA transcript. We have our little boxed ribosomes that look like this. And about every 80 nucleotides, a new one jumps on. So these little blue circles here are amino acids. And you can see that, you know, further down the transcript, there's more chains. But before this is finished, more ribosomes keep jumping on, and they form these polyribosomes that can be translating the same transcript multiple times, and this saves a lot of time and is really efficient. So I said this will be brief. It was, and this is polyribosomes, so let's move on.
Which of the following is not true regarding translation?
Which ribosomal site of protein synthesis does the initiator tRNA bind to initiation translation?
Before translation initiation, which subunit of the ribosome is recruited to the mRNA first?
Elongation factors get the energy to elongate the polypeptide chain through which of the following processes?
Only one copy of a protein can be synthesized at one time.
Here’s what students ask on this topic:
What is the role of ribosomes in translation?
Ribosomes play a crucial role in translation, the process of converting mRNA into proteins. They consist of two subunits: a small subunit and a large subunit. The small subunit is responsible for matching tRNA to mRNA codons, while the large subunit catalyzes the formation of peptide bonds between amino acids. Ribosomes have three sites: the A site (aminoacyl site) where tRNA recognizes the codon, the P site (peptidyl site) where the amino acid is added to the growing polypeptide chain, and the E site (exit site) where tRNA exits the ribosome. This coordinated action ensures the accurate and efficient synthesis of proteins.
Created using AIHow does the initiation of translation occur?
Initiation of translation begins with the binding of the initiator tRNA to the small subunit of the ribosome, along with various initiation factors (IFs and eIFs). This initiator tRNA carries methionine and binds to the P site of the small subunit. The ribosome then attaches to the 5' end of the mRNA and scans for the start codon (AUG). Once the start codon is recognized, the large subunit joins the complex, forming a complete ribosome. This marks the beginning of the elongation phase, where amino acids are sequentially added to the growing polypeptide chain.
Created using AIWhat are the differences between prokaryotic and eukaryotic translation?
Prokaryotic and eukaryotic translation differ in several key aspects. In prokaryotes, ribosomes bind to the mRNA via the Shine-Dalgarno sequence, whereas in eukaryotes, ribosomes recognize the 5' cap structure of the mRNA. Prokaryotic ribosomes are slightly smaller than eukaryotic ribosomes. Additionally, antibiotics often target prokaryotic ribosomes without affecting eukaryotic ribosomes, exploiting these structural differences. These distinctions are crucial for understanding how translation is regulated and targeted in different organisms.
Created using AIWhat are polyribosomes and their significance in translation?
Polyribosomes, or polysomes, are clusters of ribosomes that simultaneously translate a single mRNA transcript. This arrangement allows multiple copies of a protein to be synthesized concurrently, significantly increasing the efficiency of translation. Each ribosome on a polyribosome begins translation approximately every 80 nucleotides along the mRNA. This process ensures that cells can rapidly produce large quantities of proteins, which is essential for cellular function and response to environmental changes.
Created using AIWhat happens during the elongation phase of translation?
During the elongation phase of translation, amino acids are sequentially added to the growing polypeptide chain. The ribosome moves along the mRNA in a 5' to 3' direction, with tRNAs bringing specific amino acids to the ribosome. The tRNA enters the A site, where it matches its anticodon with the mRNA codon. The amino acid is then transferred to the polypeptide chain at the P site. The ribosome shifts three nucleotides, moving the tRNA to the E site, where it exits the ribosome. This cycle repeats until a stop codon is reached.
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