Introduction to Translation - Online Tutor, Practice Problems & Exam Prep

Translation is the process of protein synthesis using mRNA, facilitated by ribosomes and transfer RNAs (tRNAs). Ribosomes consist of two subunits: the small (30S in prokaryotes, 40S in eukaryotes) and large (50S in prokaryotes, 60S in eukaryotes). tRNAs carry amino acids to the ribosome, entering through the A site, where they bind to mRNA codons via anticodons. The P site holds the growing polypeptide chain, while the E site is where discharged tRNAs exit. Understanding these components is crucial for grasping the translation process and protein synthesis.

Introduction to Translation

In this video, we're going to begin our introduction to translation. And so recall from our previous lesson videos that translation is the process that builds proteins by using the encoded messages of mRNA or messenger RNA. Now in the process of translation, these structures, called ribosomes and transfer RNAs or tRNAs, are going to be very important. And so ribosomes are going to be very complex structures made of proteins and ribosomal RNA or rRNA. And these ribosomes, these complex structures, they're going to be the main structure that's important for building proteins once again, and therefore, it's the main protein that's important for performing translation.

Now throughout the process of translation, building the protein, these ribosomes rely on these transfer RNAs or these tRNAs for short. And so the transfer RNAs are going to be RNA structures themselves, but they are not going to be translated into a protein. Instead, the transfer or tRNAs are going to be important for carrying or transferring amino acids to the ribosomes during translation. And so they're pretty much bringing amino acids to the ribosomes. Now the tRNAs are going to contain anticodons. And so the anticodons are going to pair with the mRNA codons during translation. And so this pairing of the anticodons with the codons is what's going to specify one amino acid that's associated with the tRNA anticodon with, one mRNA codon. And so we'll be able to talk more details about this process as we move forward through our course.

Now one thing to note about these tRNAs is that they can really come in two states, one of two states. The first state is the charged state, the charged tRNA. Now the charge here, this term charge has nothing to do with the electrical charge. And so the tRNAs do not actually have an electrical charge. Instead, this term charge is referring to something different other than a positive or negative electrical charge. Charged tRNAs are tRNAs that are attached to an amino acid, and that is really it. Has nothing to do with electrical charge positive or negative. So charged tRNAs are the attached or tRNAs that are actually attached to an amino acid.

Now discharged tRNAs, on the other hand, again, has nothing to do with the electrical charge, positive or negative. Instead, discharged tRNAs are the opposite of charged tRNAs. Charged tRNAs are attached to an amino acid. Discharged tRNAs are not attached to an amino acid. And so we'll be able to see this down below in our image. Now in our example image down below, we're showing you the different variations of transfer RNAs or tRNAs during translation over here. Over here on this side, what we're showing you is just the process of translation. Taking the encoded messages of RNA, and translation is the process of using those encoded messages of RNA to build a protein. And of course, the process of translation relies heavily on the ribosome, which is gonna be the main structure responsible for translation. And of course the tRNAs, And the tRNAs are going to be important for bringing amino acids to the ribosome. And again, we'll talk more and more about the details introduction.

And so, taking a look at the tRNA over here, what you'll notice about the tRNA, the transfer RNA, is that it is a long RNA molecule, and it is going to be attached to an amino acid. And when it is attached to an amino acid, it is referred to as a charged tRNA. And so the amino acid in this image is being represented by this blue circle, so that would be the amino acid. Now the discharged tRNA is not going to be attached to an amino acid. You can see the amino acid attachment site is here, but there is no amino acid here. And so because there's no amino acid here, it makes this over here a discharged tRNA, not attached to an amino acid.

Now again, the tRNAs themselves are going to have anticodons, three nucleotide sequences that pair with the codons on the mRNA. And so here what we have is the anticodon on the tRNA. And notice that the anticodon on the tRNA is pairing translation, and that is what is going to help specify the process of translation. And, again, we'll talk more details, all of these details, and reveal them, as we move forward through our course. But one thing to keep in mind here is that, once again, translation is going to build proteins using the encoded messages of mRNA. It is going to rely heavily on ribosomes and transfer RNAs or tRNAs. And so we'll talk more about translation as we move forward in our course, so I'll see you all in our next video.

What type of bonding is responsible for maintaining the shape of the tRNA molecule shown in the figure?

• A. Ionic bonding between phosphates.
• B. Hydrogen bonding between base pairs of nucleotides.
• C. Van der Waals interactions between hydrogen atoms.
• D. Peptide bonding between amino acids.

The tRNA shown in the figure has its 3′ end projecting beyond its 5′ end. Which of the following processes will occur at this 3′ end?

• A. The amino acid binds covalently.
• B. The excess nucleotides (ACCA) will be cleaved off at the ribosome.
• C. The small and large subunits of the ribosome will attach to it.
• D. These nucleotides represent the anti-codon.

Ribosome Subunits

In this video, we're going to talk more details about ribosomes, specifically the ribosome subunits. And so ribosomes, which recall are the main structure responsible for translation, actually consist of 2 subunits or 2 components that are referred to as the small and large ribosomal subunits. And so each of these subunits, the small and large ribosomal subunits, are made of proteins and ribosomal RNA or rRNA. Now it turns out that the ribosomes of prokaryotes differ from the ribosomes of eukaryotes. And so notice down below in our image, we're going to be talking about prokaryotic ribosomes over here on the left-hand side, and on the right-hand side, we're going to be focusing on Eukaryotic Ribosomes. Now, again, it's very important to make sure that you're able to distinguish the complete intact ribosome from the other ribosomal subunits that come together. And so again, what you'll notice here is that there is a large ribosomal subunit and then there is a small ribosomal subunit. And the large and small ribosomal subunit need to come together to form the complete intact ribosome. Okay? And so, that's important to keep in mind. Now it turns out that prokaryotes, they actually have a complete intact ribosome with both subunits combined. That's referred to as a 70S ribosome. Okay. So the complete intact ribosome for prokaryotes with both subunits combined together is called a 70S ribosome. So we can fill that in down below in our image. Now the 70S ribosome of prokaryotes, again, it's gonna be made of these two subunits, the large ribosomal subunit and the small ribosomal subunit. The large ribosomal subunit on its own when it is separate from the small ribosomal subunit is referred to as a 50S large ribosomal subunit. And the small ribosomal subunit of prokaryotes is going to be referred to on its own as a small 30S ribosomal subunit. And so one thing to note here is that 50 + 30 does not equal 70. And that's okay. That is how this works. It is not going to be the sum of these two subunits that gives you the complete intact ribosome. Instead, these, this S here is a unit that you don't really need to worry about for the purposes of our course, but it is the Svedberg unit. And it basically describes how these ribosomes would, basically, sediment, or, centrifuge in a complex process. So you don't need to worry about this, what this S is. But what you should note - one thing that's important to note is that the 50S plus the 30S does not equal 70S, and that's okay. That's how this works. So prokaryotes have a 70S, complete intact ribosome that is made up of a large 50S subunit and a small 30S subunit. Now, eukaryotes, on the other hand, which are over here, their ribosomes, as we mentioned, are different. And so eukaryotes actually have an 80S intact ribosome, a complete intact ribosome. So when both the large and small subunits are complexed together, the entire ribosome is referred to as an 80S ribosome in eukaryotes. And so this complete intact 80S ribosome in eukaryotes, of course, is gonna be made up of smaller components, the smaller subunits, the large subunit, and the small subunit. And so the large ribosomal subunit in eukaryotes is actually going to be a 60S large ribosomal subunit. And so you can see this, the 60S subunit is this large ribosomal subunit. And the small ribosomal subunit for eukaryotes is going to be a 40S small ribosomal subunit. So you can see the 40S for the small ribosomal subunit is here. And so once again, 60 + 40 does not equal 80, but that's okay. That's how this process works. And so, the 80S ribosome is composed of the 60S and the 40S subunit. And so, this here is how it works, but how are you supposed to remember this process? How are you supposed to remember that the prokaryotic ribosome is a 70S ribosome when it's completely intact and that it's made up of a large 50S ribosomal subunit and small 30S ribosomal subunit and, also the details of the eukaryote. How are you supposed to remember that? Well, an easy way to help that helps me remember this is that, notice that all of these numbers, if you put them together, they're basically, just going 30, 40, 50, 60, 70, 80. 30, 40, 50, 60, 70, 80. So what I like to do is I write down all of those numbers in their order. So I say 30, 40, 50, and then I say, okay. Well, 60, 70, 80. And then what I like to do is I like to put them in pairs. Okay? And I say, okay, 30, 40 is the pair, 50, 60 is a pair, and 70, 80 is a pair. And so the 30, 40, because those are the smallest numbers, this is going to represent the small ribosomal subunits. And, of course, the 50, 60 is a little bit larger, so this is going to represent the large ribosomal subunits. And then, of course, the 70, 80 over here is going to be representing the complete intact ribosomes complete intact ribosomes. And so, of course, the complete intact ribosome is when the small and large ribosomal subunits come together. So now that I've got those pairings there, then I know that the smaller number within each pair is going to be prokaryotic. So I know the 30S is gonna be here, the 50S is going to be here, and the 70S is going to be here. And then the larger number in each pair is going to be eukaryotic. So you can see the 40S is here, the 60S is here, and the 80S is here. And so if you just order these numbers, 30, 40, 50, 60, 70, 80, and do what we talked about here in this video, then you'll have no problem remembering the components and the differences between prokaryotic and eukaryotic ribosomes. And so this here concludes our brief introduction to the ribosomal subunits and we'll continue to talk more about ribosomes and the process of translation as we continue to move forward in our course. So I'll see you all in our next video.

Ribosomal tRNA Binding Sites

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.

And so each of the ribosomes is going to have 3 tRNA binding sites. And so recall that the tRNAs are the transfer RNAs that are going to be attached to amino acids and bring amino acids to the ribosome. And so, the tRNA binding sites are going to be found within the ribosome, and there are 3 tRNA binding sites. The first tRNA binding site is going to be the aminoacyl tRNA binding site. Otherwise, just abbreviated as the A site. And so the A site is going to be the site where the tRNAs are going to originally enter into the ribosome. And so it holds the tRNA that's carrying the next amino acid to be added. And again, tRNAs will enter into the ribosome through the A site.

If we take a look at our image down below, what you'll notice is we've got our ribosome, our complete intact. And this right here represents our mRNA, our messenger RNA. And so 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. And again, the charge has nothing to do with the positive or negative electrical charge. Instead, the charged tRNAs are attached to amino acids. And amino, tRNAs, charged tRNAs are originally going to enter into the ribosome into the A site. So 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. Now 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. And so 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 here represents the growing polypeptide chain. And so, the P site is going to have the amino the tRNA that is bound to the growing polypeptide chain. And notice that the tRNA is going to have the anticodon, and the anticodon is going to pair with the codon of the mRNA. And so this will be a process that we'll talk more details about as we move forward in our course. Now the 3rd and final site of the tRNA, the ribosome tRNA binding site is going to be the E site or the exit site. And so the E site or the exit site, of course, is going to be where the discharged tRNAs are going to leave the ribosome from this site. And so the E site is going to be on this end of the ribosome and the E site is the exit site. And so 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. And so the discharged tRNA is without the amino acid are going to exit the ribosome through the E site. And so 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. And 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.

And, again, this is a very detailed and complex process that involves a lot of moving pieces. And so this here is really just the introduction to these 3 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.

A ribosome has three tRNA binding sites. Which answer matches the tRNA binding site with the correct function:

• A. The A-site acts as the loading site, holding the tRNA with the next amino acid in the polypeptide sequence.
• B. The E-site releases charged tRNA from the ribosome.
• C. The P-site is holding the growing strand of amino acids making up the polypeptide.
• D. A and B are correct.
• E. B and C are correct.
• F. A and C are correct.
• G. All of the above are correct.

Which of the following statements concerning ribosomes are true?

• A. Several ribosomes are often attached to and translating the same mRNA.
• B. Ribosomes join amino acids to form a polypeptide.
• C. Ribosomes have a binding site for mRNA and three binding site for tRNA molecules.
• D. No protein synthesis within a cell would occur without ribosomes.
• E. All of the above statements are true.

The direction of ribosome movement during translation is in the ______________.

• A. 3' → 5' direction of DNA.
• B. 5' → 3' direction of tRNA.
• C. 3' → 5' direction of mRNA.
• D. 5' → 3' direction of mRNA.

Many antibiotics work by blocking the function of ribosomes. Therefore, these antibiotics will:

• A. Block DNA synthesis in eukaryotic cells.
• B. Block protein synthesis in prokaryotes.
• C. Block RNA synthesis in prokaryotes.
• D. Block viral DNA in prokaryotes.
• E. Block protein synthesis in eukaryotes.

Here’s what students ask on this topic:

What is the role of ribosomes in the process of translation?

Ribosomes play a crucial role in translation, the process of protein synthesis. They are complex structures composed of proteins and ribosomal RNA (rRNA). Ribosomes consist of two subunits: a small subunit (30S in prokaryotes, 40S in eukaryotes) and a large subunit (50S in prokaryotes, 60S in eukaryotes). During translation, ribosomes facilitate the decoding of mRNA sequences into polypeptides. The ribosome's A site binds incoming tRNAs carrying amino acids, the P site holds the tRNA with the growing polypeptide chain, and the E site is where discharged tRNAs exit. This coordinated action ensures the correct assembly of amino acids into proteins.

How do tRNAs contribute to the translation process?

Transfer RNAs (tRNAs) are essential for translation, as they transport amino acids to the ribosome. Each tRNA has an anticodon that pairs with a specific mRNA codon, ensuring the correct amino acid is added to the growing polypeptide chain. tRNAs enter the ribosome at the A site, where they match their anticodon with the mRNA codon. The amino acid they carry is then transferred to the polypeptide chain at the P site. Finally, the tRNA, now discharged of its amino acid, exits the ribosome through the E site. This process ensures the accurate synthesis of proteins according to the mRNA template.

What are the differences between prokaryotic and eukaryotic ribosomes?

Prokaryotic and eukaryotic ribosomes differ in size and composition. Prokaryotic ribosomes are 70S, composed of a 50S large subunit and a 30S small subunit. Eukaryotic ribosomes are 80S, consisting of a 60S large subunit and a 40S small subunit. The 'S' stands for Svedberg units, a measure of sedimentation rate during centrifugation, not a direct sum of the subunits. These differences are crucial for the function and regulation of protein synthesis in different cellular environments. Understanding these distinctions helps in studying antibiotics that target bacterial ribosomes without affecting eukaryotic cells.

What are the three tRNA binding sites on the ribosome, and what are their functions?

The ribosome has three tRNA binding sites: the A site, P site, and E site. The A site (aminoacyl-tRNA site) is where tRNAs carrying amino acids first enter the ribosome. The P site (peptidyl-tRNA site) holds the tRNA with the growing polypeptide chain. The E site (exit site) is where discharged tRNAs, now without an amino acid, exit the ribosome. This sequential movement of tRNAs through these sites ensures the correct addition of amino acids to the polypeptide chain, facilitating efficient protein synthesis.

What is the significance of the anticodon-codon pairing during translation?

The anticodon-codon pairing is crucial for the accuracy of translation. Each tRNA has an anticodon, a sequence of three nucleotides that is complementary to an mRNA codon. This pairing ensures that the correct amino acid, carried by the tRNA, is added to the growing polypeptide chain. The specificity of this interaction is vital for the synthesis of proteins with the correct sequence of amino acids, as dictated by the mRNA template. Any errors in this pairing can lead to the incorporation of incorrect amino acids, potentially resulting in dysfunctional proteins.