Animation of Protein Synthesis (Translation) in Prokaryotes.

Alila Medical Media

25 Nov 201404:06

Summary

TLDRThis script details the process of translation initiation, elongation, and termination in prokaryotes. It describes how the small ribosomal subunit, with the aid of initiation factors IF1, IF3, and IF2, aligns the mRNA's start codon with the ribosome. The initiator tRNA carrying N-formyl-methionine is positioned, and the large subunit assembles. Elongation involves tRNAs entering the A-site, peptide bond formation, and translocation. Termination occurs upon stop codon recognition by release factors, leading to polypeptide release and ribosome disassembly for another translation cycle.

Takeaways

🌟 The initiation of translation in prokaryotes involves the separation of the small and large ribosomal subunits with the help of IF1 and IF3 initiation factors.
🔍 The small ribosomal subunit binds to the mRNA at the Shine-Dalgarno sequence, which is crucial for proper alignment of the start codon within the ribosome.
🔗 The Shine-Dalgarno sequence pairs with a complementary sequence on the 16S rRNA, ensuring the correct positioning of the start codon.
🚀 IF2 brings the initiator tRNA with the amino acid N-formyl-methionine to the complex, initiating the translation process.
🧬 The large ribosomal subunit then joins the complex, and all initiation factors are released, setting the stage for the translation elongation.
🔄 The ribosome has three sites: A-site for new tRNA, P-site for peptidyl-tRNA carrying the growing polypeptide chain, and E-site for tRNA exit.
🔑 The initiator tRNA is positioned in the P-site, which is unconventional and sets the stage for the elongation phase.
🔄 During elongation, tRNAs carrying amino acids enter the A-site, where their anticodons are matched against the mRNA codon.
🛡️ Incorrect tRNAs are rejected through a proof-reading process, ensuring only correct tRNAs participate in peptide bond formation.
🔗 Peptide bonds are formed between adjacent amino acids, and the ribosome moves one codon forward on the mRNA, shifting tRNAs from A-site to P-site and then to E-site.
🏁 Translation termination occurs when a stop codon is positioned in the A-site, recognized by a release factor that cleaves the bond between the polypeptide and tRNA, releasing the completed polypeptide.
🔄 After termination, the ribosome disassociates into subunits, ready to initiate a new round of translation.

Q & A

What are the two initiation factors that help separate the small ribosomal subunit from the large subunit in prokaryotic translation initiation?
-The two initiation factors are IF1 and IF3.
What is the purpose of the Shine-Dalgarno sequence in prokaryotic translation?
-The Shine-Dalgarno sequence is a purine-rich region that the small ribosomal subunit binds to, ensuring the start codon is in the correct position within the ribosome.
How does the initiator tRNA with the amino acid N-formyl-methionine get involved in the translation process?
-Initiation factor IF2 brings in the initiator tRNA charged with the initiator amino acid N-formyl-methionine.
What are the three sites of the ribosome, and what is the function of each site?
-The three sites are the A-site (entry for new tRNA), the P-site (occupied by peptidyl-tRNA carrying the growing polypeptide chain), and the E-site (exit for tRNA after delivering the amino acid).
Where is the initiator tRNA positioned during the initiation of translation?
-The initiator tRNA is positioned in the P-site.
What happens during the elongation phase of translation when the correct aminoacyl-tRNA enters the A-site?
-A peptide bond is made between the two now-adjacent amino acids, and the tRNA in the P-site releases the amino acids onto the tRNA in the A-site, becoming empty.
How does the ribosome move forward on the mRNA during the elongation phase?
-The ribosome moves one triplet forward on the mRNA after the peptide bond is formed and the tRNA in the P-site releases the amino acids.
What is the role of the release factor in the termination of translation?
-The release factor recognizes the stop codons in the A-site and catalyzes the cleavage of the bond between the polypeptide and the tRNA, releasing the polypeptide from the ribosome.
What occurs after the termination of translation?
-The ribosome disassociates into subunits and is ready for a new round of translation.
Why are tRNAs with incorrect anticodons rejected during the elongation phase?
-Incorrect anticodons prevent proper codon-anticodon pairing, which is essential for accurate protein synthesis; thus, they are rejected to ensure fidelity in translation.
How does the ribosome ensure the correct aminoacyl-tRNA is matched with the mRNA codon during elongation?
-The ribosome checks the incoming tRNA's anticodon against the mRNA codon in the A-site, rejecting those with incorrect anticodons and accepting the correct ones for peptide bond formation.

Outlines

00:00

🔬 Prokaryotic Translation Initiation and Ribosome Sites

This paragraph delves into the process of translation initiation in prokaryotes, highlighting the role of initiation factors IF1, IF3, and IF2. It explains how the small ribosomal subunit binds to the mRNA's Shine-Dalgarno sequence, which pairs with the 16S rRNA to position the start codon correctly. The initiator tRNA with N-formyl-methionine is brought in by IF2, and the large ribosomal subunit completes the initiation complex. The paragraph also describes the ribosome's three sites: the A-site for incoming tRNA, the P-site for peptidyl-tRNA carrying the growing polypeptide chain, and the E-site for tRNA exit.

Mindmap

Keywords

💡Ribosomal Subunit

The ribosomal subunits are the two main components of the ribosome, which is the cellular machinery responsible for protein synthesis. In prokaryotes, there are two subunits: the small subunit (30S) and the large subunit (50S). The small subunit is involved in binding the mRNA and the initiator tRNA, while the large subunit joins later to form the complete ribosome. In the script, the initiation of translation involves the separation of these subunits and their subsequent rejoining, which is crucial for the process of translation.

💡Initiation Factors (IF1, IF2, IF3)

Initiation factors are proteins that assist in the assembly of the ribosome and the initiation of translation. IF1 and IF3 help in the separation of the ribosomal subunits, while IF2 is responsible for bringing the initiator tRNA to the ribosome. These factors are essential for the correct positioning of the mRNA and the initiator tRNA, ensuring the accurate start of protein synthesis, as described in the script.

💡Shine-Dalgarno Sequence

The Shine-Dalgarno sequence is a purine-rich region found upstream of the start codon (AUG) on the mRNA in prokaryotes. It plays a critical role in the initiation of translation by base-pairing with a complementary sequence on the 16S rRNA of the small ribosomal subunit. This interaction positions the start codon correctly within the ribosome for the initiator tRNA to bind, as mentioned in the script.

💡Start Codon

The start codon is a specific sequence of three nucleotides (AUG) on the mRNA that signals the beginning of the coding region for a protein. It is recognized by the initiator tRNA, which carries the first amino acid to be added to the growing polypeptide chain. In the script, the correct positioning of the start codon is ensured by the base-pairing with the Shine-Dalgarno sequence.

💡Initiator tRNA

The initiator tRNA is a specific type of transfer RNA (tRNA) that carries the first amino acid, N-formyl-methionine, to the ribosome during the initiation phase of translation. It is brought to the ribosome by the initiation factor IF2, as described in the script, and is positioned in the P-site of the ribosome, ready to start protein synthesis.

💡A-site

The A-site, or the aminoacyl-tRNA site, is one of the three sites on the ribosome where new tRNA carrying an amino acid enters during the elongation phase of translation. It is the entry point for the tRNA whose anticodon will pair with the mRNA codon. In the script, the A-site is where the proof-reading process occurs, ensuring that only correct tRNAs participate in peptide bond formation.

💡P-site

The P-site, or the peptidyl-tRNA site, is where the tRNA carrying the growing polypeptide chain is located during translation. It is occupied by the tRNA that has just contributed an amino acid to the chain. In the script, the initiator tRNA is initially positioned in the P-site, and during elongation, the P-site is where the peptidyl-tRNA resides before it moves to the E-site.

💡E-site

The E-site, or the exit site, is where the tRNA that has delivered its amino acid exits the ribosome. After the peptide bond is formed and the ribosome translocates, the now-empty tRNA moves from the P-site to the E-site before being released from the ribosome, as described in the script.

💡Elongation

Elongation is the phase of translation during which the ribosome synthesizes the protein by linking amino acids together in a sequence determined by the mRNA codons. It involves the movement of the ribosome along the mRNA, the entry of new tRNAs into the A-site, and the formation of peptide bonds. The script describes how the ribosome moves one triplet forward on the mRNA after each peptide bond is formed.

💡Termination

Termination is the final phase of translation when the synthesis of the protein is completed. It occurs when one of the three stop codons (UAA, UAG, UGA) is positioned in the A-site of the ribosome, signaling the end of the coding sequence. In the script, the release factor recognizes the stop codon and catalyzes the release of the completed polypeptide chain from the tRNA, marking the end of translation.

💡Release Factor

A release factor is a protein that recognizes the stop codons during the termination phase of translation. It binds to the A-site of the ribosome when a stop codon is present and catalyzes the cleavage of the bond between the polypeptide and the tRNA, releasing the completed protein. The script mentions the role of the release factor in recognizing the stop codons and facilitating the release of the polypeptide.

Highlights

Prokaryotic translation initiation involves separation of the small and large ribosomal subunits with the help of IF1 and IF3.

The small ribosomal subunit binds to the Shine-Dalgarno sequence upstream of the AUG start codon on mRNA.

The Shine-Dalgarno sequence pairs with a complementary sequence on the 16S rRNA, ensuring proper start codon alignment.

IF2 brings the initiator tRNA with N-formyl-methionine to the translation initiation complex.

The large ribosomal subunit joins the complex, and all initiation factors are released to start translation.

The ribosome has three sites: A-site for new tRNA, P-site for peptidyl-tRNA, and E-site for tRNA exit.

The initiator tRNA is positioned in the P-site during translation initiation.

Elongation begins with a new tRNA entering the A-site and matching its anticodon to the mRNA codon.

Incorrect tRNAs are rejected during the proof-reading process at the A-site.

Peptide bond formation occurs between adjacent amino acids when the correct tRNA is in the A-site.

The tRNA in the P-site releases amino acids and moves to the E-site as the ribosome translocates.

The A-site becomes unoccupied and ready for a new tRNA after each translocation step.

Translation termination occurs when a stop codon is positioned in the A-site and recognized by a release factor.

The release factor binding catalyzes the cleavage of the bond between the polypeptide and tRNA.

The polypeptide is released, and the ribosome disassociates into subunits for another round of translation.

The process of translation in prokaryotes is a well-coordinated sequence of events involving multiple components.

Translation efficiency is ensured by the precise interaction between mRNA, tRNA, and ribosomal subunits.

The ribosome's three sites play crucial roles in the translation process, facilitating amino acid addition and peptide chain elongation.

Termination of translation is a critical step that marks the end of protein synthesis and prepares the ribosome for a new cycle.