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 the next amino acid is added to the growing polypeptide chain in the P site, and exiting through the E site. This intricate process is essential for building proteins and relies on the specific pairing of tRNA anticodons with mRNA codons.

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. Ribosomes are going to be very complex structures made of proteins and ribosomal RNA or rRNA. These ribosomes, these complex structures, are 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. Throughout the process of translation, these ribosomes rely on these transfer RNAs or tRNAs for short. Transfer RNAs are going to be RNA structures themselves, but they are not translated into a protein. Instead, the transfer or tRNAs are important for carrying or transferring amino acids to the ribosomes during translation, essentially bringing amino acids to the ribosomes. The tRNAs contain anticodons. The anticodons are going to 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 these tRNAs is that they can really come in two states. The first state is the charged state, the charged tRNA. The charge here, this term charge has nothing to do with the electrical charge. The tRNAs do not actually 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. 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. Discharged tRNAs are not attached to an amino acid.

In our example image below, we're showing you the different variations of transfer RNAs or tRNAs during translation. Over here on this side, what we're showing you is the process of translation. Translation is the process of using the encoded messages of RNA to build a protein. This process relies heavily on the ribosome, which is going to be the main structure responsible for translation, and of course the tRNAs. The tRNAs are important for bringing amino acids to the ribosome. Taking a look at the tRNA, you'll notice that it is a long RNA molecule, and it is going to be 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 being represented by this blue circle. The discharge 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. Again, the tRNAs themselves are going to have anticodons, three nucleotide sequences that pair with the codons on the mRNA. Here what we have is the anticodon on the tRNA. Notice that the anticodon on the tRNA is pairing translation, and that is what is going to help specify the process of translation. We'll talk more details, all of these details, and reveal them as we move forward through our course. 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. Ribosomes, which recall are the main structure responsible for translation, actually consist of two subunits or two components that are referred to as the small and large ribosomal subunits. Each of these subunits, the small and large ribosomal subunits, are made of proteins and ribosomal RNA or rRNA. It turns out that the ribosomes of prokaryotes differ from the ribosomes of eukaryotes. Notice down below in our image, we're going to be talking about prokaryotic ribosomes on the left-hand side, and on the right-hand side, we're going to be focusing on eukaryotic ribosomes. 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. What you'll notice here is that there is a large ribosomal subunit and then there is a small ribosomal subunit. The large and small ribosomal subunit need to come together to form the complete intact ribosome. That's important to keep in mind. Prokaryotes actually have a complete intact ribosome with both subunits combined, referred to as a 70S ribosome. The 70S ribosome of prokaryotes is made up of two subunits: a 50S large ribosomal subunit and a 30S small ribosomal subunit. One thing to note here is that 50+30 does not equal 70 and that's okay. This difference is due to the Svedberg unit, which describes how ribosomes sediment during centrifugation in a complex process. You don't need to worry about the specifics of this unit for our course. Prokaryotes have a 70S, complete intact ribosome that is made up of a large 50S subunit and a small 30S subunit. Eukaryotes, on the other hand, have an 80S intact, complete ribosome when both the large and small subunits are complexed together. This complete intact 80S ribosome in eukaryotes is made up of smaller components: the large subunit and the small subunit. The large ribosomal subunit in eukaryotes is a 60S large ribosomal subunit, and the small ribosomal subunit for eukaryotes is a 40S small ribosomal subunit. Again, 60+40 does not equal 80, but that's how this process works. The process is represented by the numbers 30, 40, 50, 60, 70, 80. To remember this, write down these numbers in their order, put them in pairs, and assign the smaller number to the prokaryotes and the larger to the eukaryotes. This easy method helps you remember the components and the differences between prokaryotic and eukaryotic ribosomes. This 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. 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 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 going to be the aminoacyl tRNA binding site, otherwise just abbreviated as the A site. The A site is 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.

As shown in the image, this represents the mRNA, our messenger RNA. The ribosome receives tRNAs like this one right here; this box represents the tRNA. Since it's attached to an amino acid, this little purple circle represents an amino acid. That makes this tRNA a charged tRNA. Again, the charge has nothing to do with the positive or negative electrical charge. Instead, the charged tRNAs are attached to amino acids. Amino, tRNAs, charged tRNAs originally enter into the ribosome into the A site. The first site here is the A site.

The second ribosomal tRNA binding site is the P site or the peptidyl tRNA binding site, otherwise known as the P site. The P site holds the tRNA that's carrying the growing polypeptide chain or the growing protein chain. The image shows the P site in the middle holding the tRNA attached to this growing polypeptide chain. The P site contains the tRNA bound to the growing polypeptide chain. Notice that the tRNA has the anticodon, and the anticodon pairs with the codon of the mRNA. We'll talk more details about this process as we move forward in our course.

The third and final site of the tRNA, the ribosome tRNA binding site is the E site or the exit site. The E site, of course, is where the discharged tRNAs leave the ribosome from this site. The E site is on this end of the ribosome. The discharged tRNAs, which again have nothing to do with the electrical charge, are not attached to an amino acid because the amino acid was transferred over to this growing chain, this growing polypeptide chain. The discharged tRNAs without the amino acid exit the ribosome through the E site.

Here is what we are seeing: charged tRNAs bring amino acids to the ribosome and enter into the A site. Then the P site contains the growing polypeptide chain where the amino acid is added to the growing polypeptide chain. The ribosome continues to shift along the mRNA; the tRNAs in the P site shift into the E site and then eventually exit the ribosome in this way. Essentially, 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. 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 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 polypeptide chains. They provide binding sites for transfer RNAs (tRNAs) and catalyze the formation of peptide bonds between amino acids, thus building the protein. The ribosome's A site accepts incoming tRNAs, the P site holds the tRNA with the growing polypeptide chain, and the E site is where discharged tRNAs exit. This coordinated action ensures accurate and efficient protein synthesis.

How do tRNAs function in the process of translation?

Transfer RNAs (tRNAs) are essential for translation, the process of protein synthesis. Each tRNA molecule carries a specific amino acid to the ribosome, where proteins are assembled. tRNAs have an anticodon region that pairs with complementary codons on the mRNA strand, 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. The amino acid is then transferred to the growing chain at the P site. Finally, the tRNA, now without an amino acid, exits the ribosome through the E site. This cycle continues until the entire protein is synthesized, ensuring the correct sequence of amino acids as dictated by the mRNA.

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 larger, at 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 significant because they affect the ribosome's function and interaction with antibiotics. Some antibiotics specifically target prokaryotic ribosomes, inhibiting bacterial protein synthesis without affecting eukaryotic cells. Understanding these differences is crucial for developing treatments and studying cellular processes.

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 incoming tRNAs carrying amino acids 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 the A, P, and E sites ensures the correct addition of amino acids to the polypeptide chain, facilitating efficient and accurate protein synthesis.

How do charged and discharged tRNAs differ?

Charged and discharged tRNAs differ based on their attachment to amino acids. Charged tRNAs are bound to an amino acid, ready to deliver it to the ribosome during translation. This attachment is crucial for adding the correct amino acid to the growing polypeptide chain. Discharged tRNAs, on the other hand, have already delivered their amino acid and are no longer attached to one. They exit the ribosome through the E site and can be recharged with a new amino acid by specific enzymes called aminoacyl-tRNA synthetases, preparing them for another round of translation.