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 aminoacyl (A) site, transferring to the peptidyl (P) site, and exiting from the exit (E) site. Charged tRNAs are attached to amino acids, while discharged tRNAs are not. Understanding these components is crucial for grasping the translation process.

Introduction to Translation

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

Throughout the process of translation and building the protein, these ribosomes rely on these transfer RNAs or tRNAs for short. The transfer RNAs are RNA structures themselves, but they are not going to be translated into a protein. Instead, the transfer or tRNAs are important for carrying or transferring amino acids to the ribosomes during translation. They bring amino acids to the ribosomes. The tRNAs contain anticodons.

The anticodons pair with the mRNA codons during translation. This pairing of the anticodons with the codons specifies one amino acid that's associated with the tRNA anticodon with one mRNA codon. We'll be able to talk more details about this process as we move forward through our course. One thing to note about tRNA is that they can really come in one of two states. The first state is the charged state, the charged tRNA.

The term 'charge' here has nothing to do with electrical charge. The tRNAs do not have an electrical charge. Instead, this term charge refers 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 it. It has nothing to do with an electrical charge positive or negative.

So, charged tRNAs are the attached tRNAs that are actually attached to an amino acid. Discharged tRNAs, on the other hand, again, have 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, and discharged tRNAs are not attached to an amino acid.

We'll be able to see this in our example image below. We're showing you the different variations of transfer RNAs or tRNAs during translation. What we're showing you here 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. The process of translation relies heavily on the ribosome, which is the main structure responsible for translation.

The tRNAs are important for bringing amino acids to the ribosome. We'll talk more and more about the details of translation as we move forward through our course. This is just the introduction. Taking a look at the tRNA, what you'll notice about the tRNA, the transfer RNA, is that it is a long RNA molecule, and it is attached to an amino acid. When it is attached to an amino acid, it is referred to as a charged tRNA.

The amino acid in this image is represented by a blue circle, so that would be the amino acid. 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. Because there's no amino acid here, it makes this a discharged tRNA, not attached to an amino acid. The tRNAs themselves have anticodons, 3-nucleotide sequences that pair with the codons on the mRNA.

Here, we have the anticodon on the tRNA. Notice that the anticodon on the tRNA is pairing with this codon here on the mRNA. This is going to continue to occur throughout the process of translation, and that is what is going to help specify the process of translation. We'll talk more details, 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. 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 going to be made of these 2 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 2 subunits that gives you the complete intact ribosome.

Instead, 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 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, 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 going to 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 small ribosomal subunit is here. And so once again, 60 plus 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 70 s ribosome when it's completely intact and that it's made up of a large fifty s ribosomal subunit and small 30 s ribosomal subunit and, also the details of the eukaryote. How are you supposed to remember that?

Well, an easy way 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 going to 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.

Each of the ribosomes is going to have 3 tRNA binding sites. Recall that the tRNAs are the transfer RNAs that are going to be attached to amino acids and bring amino acids to the ribosome. The tRNA binding sites are found within the ribosome, and there are 3 tRNA binding sites. The first tRNA binding site is the aminoacyl tRNA binding site, otherwise just abbreviated as the A site.

The A site is going to be the site where the tRNAs originally enter into the ribosome. It holds the tRNA that's carrying the next amino acid to be added. tRNAs will enter into the ribosome through the A site. If we take a look at our image down below, you'll notice we've got our ribosome, our complete intact ribosome here in the background. The complete intact ribosome is going to be bound to our mRNA.

This right here represents our mRNA, our messenger RNA. 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. The charge has nothing to do with the positive or negative electrical charge but instead indicates that tRNAs are attached to amino acids. Charged tRNAs originally enter into the ribosome into the A site. 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.

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. 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 right here represents the growing polypeptide chain. The P site will have the amino acid attached tRNA, that is bound to the growing polypeptide chain. Notice that the tRNA is going to have the anticodon and the anticodon is going to pair with the codon of the mRNA. This will be a process that we'll talk more details about as we move forward in our course.

The third and final site of the ribosome tRNA binding site is the E site or the exit site. The E site, of course, is going to be where the discharged tRNAs are going to leave the ribosome from this site. The E site is going to be on this end of the ribosome and the E site is the exit site. 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. So, the discharged tRNAs without the amino acid are going to exit the ribosome through the E site.

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. 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. Again, this is a very detailed and complex process that involves a lot of moving pieces.

This here is really just the introduction to these three 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 the process of translation, which is the synthesis of proteins using mRNA. 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). These subunits come together to form a complete ribosome. During translation, ribosomes facilitate the binding of tRNAs to mRNA codons, ensuring the correct sequence of amino acids is added to the growing polypeptide chain. The ribosome has three tRNA binding sites: the A site (aminoacyl), the P site (peptidyl), and the E site (exit), which coordinate the entry, peptide bond formation, and exit of tRNAs, respectively.

How do tRNAs contribute to the translation process?

tRNAs, or transfer RNAs, are essential for the translation process as they carry 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 bring the next amino acid to be added. The amino acid is then transferred to the growing polypeptide chain at the P site. Finally, the tRNA, now without an amino acid (discharged tRNA), exits the ribosome through the E site. This cycle continues until the entire protein is synthesized.

What are the differences between prokaryotic and eukaryotic ribosomes?

Prokaryotic and eukaryotic ribosomes differ in their 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, which measure the rate of sedimentation during centrifugation, not a direct sum of the subunits. These differences are crucial for the function and regulation of protein synthesis in prokaryotic and 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 (aminoacyl), the P site (peptidyl), and the E site (exit). The A site is where tRNAs carrying amino acids enter the ribosome. The P site holds the tRNA with the growing polypeptide chain, facilitating peptide bond formation. The E site is where discharged tRNAs, which no longer carry an amino acid, exit the ribosome. These sites ensure the correct sequence of amino acids is added to the polypeptide chain during translation.

What is the difference between charged and discharged tRNAs?

Charged tRNAs are tRNAs that are attached to an amino acid, ready to participate in protein synthesis. Discharged tRNAs, on the other hand, are tRNAs that have already transferred their amino acid to the growing polypeptide chain and are no longer attached to an amino acid. The term 'charged' does not refer to electrical charge but rather to the presence of an amino acid. Charged tRNAs enter the ribosome at the A site, while discharged tRNAs exit through the E site.