Animation of Protein Synthesis (Translation) in Prokaryotes.
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
🔬 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
💡Initiation Factors (IF1, IF2, IF3)
💡Shine-Dalgarno Sequence
💡Start Codon
💡Initiator tRNA
💡A-site
💡P-site
💡E-site
💡Elongation
💡Termination
💡Release Factor
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.
Transcripts
Initiation of translation in prokaryotes: The small ribosomal subunit is separated from
the large subunit with the help of two initiation factors: IF1 and IF3. This complex then binds
a to purine-rich region -- the Shine-Dalgarno sequence -- upstream of the AUG start codon
on the mRNA. The Shine-Dalgarno sequence is base-paired to a complementary sequence on
the 16S rRNA - a component of the small subunit. This alignment ensures that the start codon
is in the right position within the ribosome. Another initiation factor - IF2 - brings in
the initiator tRNA charged with the initiator amino acid N-formyl-methionine. The large
ribosomal subunit joins the complex and all initiation factors are released. The ribosome
has three sites: the A-site is the entry site for new tRNA charged with amino-acid or aminoacyl-tRNA;
the P-site is occupied by peptidyl-tRNA - the tRNA that carries the growing polypeptide
chain; the E-site is the exit site for the tRNA after it's done delivering the amino
acid. The initiator tRNA is positioned in the P-site.
Elongation: A new tRNA carrying an amino acid enters the A-site of the ribosome. On the
ribosome, the anticodon of the incoming tRNA is matched against the mRNA codon positioned
in the A-site. During this proof-reading, tRNA with incorrect anticodons are rejected
and replaced by new tRNA that are again checked. When the right aminoacyl-tRNA enters the A-site,
a peptide bond is made between the two now-adjacent amino-acids. As the peptide bond is formed,
the tRNA in the P-site releases the amino-acids onto the tRNA in the A-site and becomes empty.
At the same time, the ribosome moves one triplet forward on the mRNA. As a result, the empty
tRNA is now in the E-site and the peptidyl tRNA is in the P-site. The A-site is now unoccupied
and is ready to accept a new tRNA. The cycle is repeated for each codon on the mRNA.
Termination: Termination happens when one of the three stop codons is positioned in
the A-site. No tRNA can fit in the A-site at that point as there are no tRNA that match
the sequence. Instead, these codons are recognized by a protein, a release factor. Binding of
the release factor catalyzes the cleavage of the bond between the polypeptide and the
tRNA. The polypeptide is released from the ribosome. The ribosome is disassociated into
subunits and is ready for a new round of translation.
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