Steps of Translation - Online Tutor, Practice Problems & Exam Prep

Translation consists of three main steps: initiation, elongation, and termination. During initiation, the small ribosomal subunit binds to messenger RNA (mRNA) and transfer RNA (tRNA), with the start codon AUG signaling the beginning of the polypeptide chain, which starts with methionine (MET). In elongation, amino acids are sequentially added to the growing chain through peptide bonds, facilitated by tRNAs entering the ribosome's A site. Finally, termination occurs when a stop codon triggers a release factor, cleaving the polypeptide chain and disassembling the translation complex.

1) Initiation of Translation

In this video, we're going to begin our lesson on the steps of translation. And so very similarly to transcription, the process of translation also consists of 3 steps, and they are named the same as they are named in transcription. So it starts with the initiation process, and then it moves on into the elongation process. And then last but not least, it moves on to the termination process. And so as we move forward in our course, we're going to talk about each of these three steps of translation in their own separate videos, starting with the initiation process.

And so in the initiation of translation, of course, we know initiation just means the start or the beginning of the process. And during the initiation of translation, it turns out that the small ribosomal subunit of the ribosome is actually first going to bind to the messenger RNA and a tRNA before the large ribosomal subunit even comes into play and binds. And so if we take a look at our image down below at the initiation of translation, notice that at the very beginning, the small ribosomal subunit, which we're showing you here, is going to bind to the messenger RNA, the mRNA first. And, the messenger RNA, is then going to associate with the tRNA that you see here. And so the small ribosomal subunit is going to bind to the messenger RNA and the tRNA before this large ribosomal subunit over here, the large ribosomal subunit, even comes into play. And so that's really the sequence of events here, the small ribosomal subunit binding to the mRNA, then the tRNA, and then lastly here, the large ribosomal subunit is the last component to come into play during initiation.

Now one thing to note is that, of course, the mRNA, the messenger RNA is going to contain the codons, the 3 nucleotide sequences. And so the very first codon is going to be the start codon. It's what's known as the start codon. And the start codon is going to be AUG, which specifies the amino acid methionine or MET. And so, the start codon AUG that specifies the amino acid methionine is going to initiate the start of translation during this initiation process. And so what you'll notice here is that here in the mRNA we have the codon AUG, and this is going to be the start codon. And, of course, the codons are going to specify amino acids through the tRNAs, the transfer RNAs, which are going to have anticodons that are complementary to the codon. And so the tRNA, of course, is going to be a charged tRNA that is attached to an amino acid. And this amino acid, that corresponds with the start codon is going to be methionine, which is abbreviated as MET. And so we can put MET in here, And so that is going to be, the first amino acid in the chain of, the polypeptide chain. Now it turns out that the initiation of translation is actually can be quite a complex process. It actually involves several proteins that are called initiation factors, which we're actually not showing you here in this image. And, translation the initiation requires energy as well, which we are showing you the energy here, to remind you that it does require energy. And so ultimately, at the end of, the initiation of translation, we have the complete intact ribosome bound to the messenger RNA and the very, very first tRNA, that corresponds with the start codon, and the amino acid methionine.

And so, this here concludes our introduction to the initiation of translation and the steps of translation. And we'll be able to talk more about these steps of translation as we move forward in our course, continuing with elongation and then, of course, ending with termination. So I'll see you all in our next video.

2) Elongation of Translation

In this video, we're going to talk about the second step of translation, which is the elongation of translation. And so of course, elongation just means making something longer. And what's going to be made longer is the growing polypeptide chain, the growing amino acid chain. And so during the elongation of termination, amino acids are going to be added one by one to the previous amino acid at the C-terminus of the growing chain. And so therefore, this means that the polypeptide chain is going to be growing from its N-terminus to its C-terminus. Now, the ribosome, again, is going to be the main structure involved with translation, and it's going to be reading the mRNA, the messenger RNA, in codons. It's going to be reading the mRNA codons from the 5' end of the mRNA to the 3' end of the mRNA. And as it reads these codons, these three nucleotide sequences, the ribosome is going to be pairing each of the mRNA codons with the correct respective tRNA anticodons. And those tRNAs, we know, are going to be specifying one amino acid. And so each codon will specify one amino acid by pairing with a tRNA that is attached to that amino acid.

Now the way that translation elongation works is that new tRNAs that are charged and attached to amino acids are going to enter the ribosome's A site and then shift into the ribosome's P site, and then finally, they're going to exit the ribosome through the ribosome's E site before exiting. And so if we take a look at our image down below at the elongation of translation, we can better understand how this process works. And so here at the very beginning, what we're showing you is the end result of the initiation of translation, where we have the small and large ribosomal subunits are intact and bound to the very first tRNA, and the messenger RNA, the mRNA. And so what you can see here is that charged tRNAs, or tRNAs that are attached to amino acids, are going to enter into the ribosome into the ribosome's A site. So that's what we have here as the very first step, that charged tRNAs are going to enter into the ribosome via the A site.

And then, what's going to happen is, a peptide bond is going to be formed. And recall that a peptide bond is a covalent bond between amino acids. And so what happens here is that the first amino acid, in this position is going to be covalently linked to the next amino acid. And so, it gets passed on to this tRNA here. And so you can see they've been covalently linked, these two amino acids. So we have a growing amino acid chain here. Now, what happens is, the ribosome is going to continue to shift along the mRNA, and that causes the discharged tRNA. Remember, discharged tRNAs are tRNAs that are not attached to amino acids because, again, its amino acid was linked to the previous amino acid. And so the discharged tRNA is going to enter and exit, enter the E site and exit the ribosome through the E site. And so you can see here that the discharged tRNA is exiting through the E site. And meanwhile, the other tRNA is shifting into the P site. So the tRNA is going to shift into the P site. And ultimately, the process peptide bond would be formed between that amino acid, and then, again, the process would just continuously repeat over and over and over again to continuously add amino acids and grow this polypeptide chain. And so that is going to be the elongation of translation, and we'll be able to talk about the final step of translation, the termination of translation in our next video. So I'll see you all there.

3) Termination of Translation

In this video, we're going to talk about the 3rd and final step of translation, which is the termination of translation. And so of course, termination means to put something to an end. And so during termination, the process of translation will be coming to an end. And so during the termination of translation, a stop codon is going to reach the ribosome's A site and that is going to trigger a release factor protein to bind. And so if we take a look at our image down below, we can see that we have our growing polypeptide chain here. And here what we have is the next codon, but this codon, notice, is a stop codon, UGA. And so the stop codon is not going to be associated with a tRNA. Instead, the stop codon is going to trigger a release factor protein, this orange protein, to bind. And so when the release factor protein is bound, it's going to trigger a series of events. First, the polypeptide chain is going to be cleaved and released from the tRNA. And so you can see that the tRNA over here is no longer bound to the polypeptide chain over here as it was over here on this side. And so what we end up getting is our final polypeptide chain is right here at this position that is going to be released. And also, the entire translation assembly is going to come apart as well, due to this release factor. And so the release factor gets the release, the mRNA is released, the small and large ribosomal complex are going to dissociate from each other. And again, the final protein chain, polypeptide chain is also released. And so that terminates the entire process of translation. And so this here concludes our brief lesson on the termination of translation, and we'll be able to get some practice applying the concepts that we've talked about here and the steps of translation as we move forward in our course. So I'll see you all in our next video.

The tRNA for which amino acid is the first to enter the ribosome?

• A. Arginine.
• B. Lysine.
• C. Methionine.
• D. Histidine.

Which of the following processes is the first event to take place in translation?

• A. Base pairing of charged methionine-tRNA to AUG of the messenger RNA.
• B. Binding of the larger ribosomal subunit to smaller ribosomal subunits.
• C. The ribosome reaches a stop codon.
• D. The small subunit of the ribosome recognizes and attaches to the mRNA.

When is a peptide bond formed during the process of translation?

• A. During the elongation phase, just after a tRNA charged with the next amino acid binds to the A site.
• B. During the termination phase, just after the release factor binds to the A site.
• C. During the elongation phase, just after a tRNA that has lost its amino acid and exits the E site.

Which of the following does not occur during translation's termination step?

• A. The first tRNA brings the amino acid methionine to the ribosome.
• B. The small and large ribosomal subunits separate from each other.
• C. The polypeptide is released from the ribosome.
• D. A "stop" codon is reached by the ribosome along the mRNA.

What is the function of the release factor during translation?

• A. It binds to the stop codon in the A site in place of a tRNA.
• B. It releases the amino acid from its tRNA to allow the amino acid to be added to the growing polypeptide.
• C. It supplies a source of energy for termination of translation and the release of the polypeptide.
• D. It releases the ribosome from the rough endoplasmic reticulum and allows the polypeptide to enter the cytosol.

Here’s what students ask on this topic:

What are the three main steps of translation in protein synthesis?

The three main steps of translation in protein synthesis are initiation, elongation, and termination. During initiation, the small ribosomal subunit binds to the messenger RNA (mRNA) and transfer RNA (tRNA), with the start codon AUG signaling the beginning of the polypeptide chain, which starts with methionine (MET). In elongation, amino acids are sequentially added to the growing chain as the ribosome reads mRNA codons. Finally, termination occurs when a stop codon triggers the release of the completed polypeptide chain and disassembly of the translation complex, concluding the process.

What happens during the initiation step of translation?

During the initiation step of translation, the small ribosomal subunit binds to the messenger RNA (mRNA) and a transfer RNA (tRNA) that carries the amino acid methionine (MET). The start codon AUG on the mRNA signals the beginning of the polypeptide chain. The large ribosomal subunit then joins the complex, forming a complete ribosome. This assembly positions the tRNA carrying methionine in the ribosome's P site, ready to start the elongation process.

How does elongation occur in the translation process?

Elongation in translation involves the sequential addition of amino acids to the growing polypeptide chain. The ribosome reads mRNA codons from the 5' to the 3' end. Charged tRNAs carrying specific amino acids enter the ribosome's A site, where their anticodons pair with the mRNA codons. A peptide bond forms between the amino acid in the A site and the growing chain in the P site. The ribosome then shifts, moving the tRNA to the P site and the discharged tRNA to the E site, where it exits the ribosome. This cycle repeats, elongating the polypeptide chain.

What triggers the termination of translation?

Termination of translation is triggered when a stop codon (UAA, UAG, or UGA) reaches the ribosome's A site. These stop codons do not code for any amino acids and instead signal the binding of a release factor protein. The release factor promotes the cleavage and release of the completed polypeptide chain from the tRNA. Subsequently, the translation complex, including the ribosomal subunits, mRNA, and tRNA, disassembles, concluding the translation process.

What role do tRNAs play in the translation process?

Transfer RNAs (tRNAs) play a crucial role in translation by delivering specific amino acids to the ribosome, where they are added to the growing polypeptide chain. Each tRNA has an anticodon that is complementary to an mRNA codon, ensuring the correct amino acid is incorporated. Charged tRNAs, carrying amino acids, enter the ribosome's A site, pair with the mRNA codon, and contribute their amino acid to the chain through peptide bond formation. The tRNA then shifts to the P site and exits through the E site after its amino acid is added.