Translation elongation | translation in prokaryotes lecture 4

Summary

This video delves into the elongation phase of protein synthesis in prokaryotes. It begins with the binding of charged tRNAs to the A-site of the ribosome, guided by elongation factor EF-Tu. Peptide bonds are formed between amino acids, catalyzed by the peptidyl transferase enzyme in the 50S subunit. Translocation follows, with elongation factor EF-G driving the ribosome's movement along the mRNA. The process repeats, adding amino acids to the growing chain until a stop codon is reached. The video provides an in-depth explanation of each step, emphasizing the role of GTP hydrolysis and the recycling of elongation factors.

Takeaways

• 😀 Elongation phase in protein synthesis involves the addition of amino acids to a growing polypeptide chain.
• 😀 tRNA molecules carry specific amino acids and bind to the ribosome's A site during elongation.
• 😀 The elongation factor EF-Tu aids in bringing the correct tRNA to the A site by binding with GTP.
• 😀 The codon-anticodon interaction ensures that the correct tRNA binds to the ribosome's A site.
• 😀 Once the tRNA binds to the A site, EF-Tu hydrolyzes GTP to GDP and dissociates from the ribosome.
• 😀 Peptide bond formation occurs through the enzyme peptidyl transferase, found in the 50S subunit of the ribosome.
• 😀 Peptidyl transferase catalyzes the transfer of the amino acid from the tRNA in the P site to the tRNA in the A site.
• 😀 Ribosomal translocation is the process where the ribosome moves one codon along the mRNA, facilitated by EF-G and GTP.
• 😀 EF-G hydrolyzes GTP to provide the energy needed for ribosomal translocation.
• 😀 Uncharged tRNAs are released from the E site after the ribosome translocates and shifts along the mRNA.
• 😀 The elongation cycle continues until the ribosome reaches a stop codon, signaling the termination of protein synthesis.

Q & A

What is the first step in the elongation phase of protein synthesis?

The first step in the elongation phase is the binding of a charged tRNA to the A site of the ribosome. Each tRNA brings a specific amino acid corresponding to the mRNA codon, and this binding is facilitated by elongation factor EF-Tu.

How does the elongation factor EF-Tu assist in tRNA binding?

EF-Tu binds to the tRNA and GTP, helping bring the tRNA to the ribosome. Once the tRNA matches the codon with its anticodon in the A site, the GTP is hydrolyzed to GDP, releasing EF-Tu.

What happens during the second stage of elongation?

In the second stage, known as peptide bond formation, the amino acid in the P site is transferred to the tRNA in the A site, catalyzed by the enzyme peptidyl transferase. This forms a new peptide bond, extending the polypeptide chain.

What is the role of peptidyl transferase in protein elongation?

Peptidyl transferase, an enzyme found in the 50S subunit of the ribosome, catalyzes the formation of peptide bonds between amino acids, transferring the amino acid from the P site tRNA to the A site tRNA.

What happens during translocation in the elongation process?

During translocation, the ribosome moves along the mRNA by one codon, shifting the tRNAs from the A site to the P site and from the P site to the E site. This step is powered by elongation factor EF-G and involves the hydrolysis of GTP.

What is the significance of the E site in protein synthesis?

The E site, or exit site, is where the uncharged tRNA exits the ribosome after its amino acid has been transferred. It becomes free after translocation so that the ribosome can accept the next tRNA carrying an amino acid.

What role does EF-G play in the elongation phase?

EF-G is an elongation factor that facilitates translocation. It binds to the ribosome with GTP, and upon GTP hydrolysis, it powers the ribosome to move one codon along the mRNA, shifting the tRNAs accordingly.

What is the function of EFS in the elongation phase?

EFS helps in recycling GTP for elongation factor EF-Tu. It exchanges the GDP bound to EF-Tu with a new GTP, enabling EF-Tu to participate in future tRNA binding events.

What causes the release of EF-Tu from the ribosome?

EF-Tu is released from the ribosome after GTP hydrolysis, once the tRNA has successfully matched the codon and anticodon. This ensures that EF-Tu is free to assist in the next cycle of elongation.

When does protein elongation stop during translation?

Protein elongation stops when the ribosome encounters a stop codon on the mRNA. At this point, the termination phase begins, and no more amino acids are added to the polypeptide chain.