Podcast
Questions and Answers
Which of the following is NOT a stop codon in most species?
Which of the following is NOT a stop codon in most species?
- UGU (correct)
- UGA
- UAA
- UAG
Which release factor in bacteria recognizes both UAA and UGA stop codons?
Which release factor in bacteria recognizes both UAA and UGA stop codons?
- RF2 (correct)
- RF1
- RF3
- eRF
What is the primary function of RF3 in bacteria?
What is the primary function of RF3 in bacteria?
- Recognizing UAA and UGA stop codons
- Recognizing UAA and UAG stop codons
- Recognizing all three stop codons
- Facilitating the termination process by binding GTP (correct)
Which of the following is an example of a post-translational modification?
Which of the following is an example of a post-translational modification?
What is the significance of the N-terminal and C-terminal ends of a polypeptide chain?
What is the significance of the N-terminal and C-terminal ends of a polypeptide chain?
What is the name of the modified methionine carried by the initiator tRNA in bacteria?
What is the name of the modified methionine carried by the initiator tRNA in bacteria?
What is the purpose of the Shine-Dalgarno sequence in the mRNA?
What is the purpose of the Shine-Dalgarno sequence in the mRNA?
Which of the following is NOT a requirement for the formation of the initiation complex in translation?
Which of the following is NOT a requirement for the formation of the initiation complex in translation?
What happens to the GTP molecule during the initiation of translation?
What happens to the GTP molecule during the initiation of translation?
Which ribosomal site does the charged initiator tRNA enter during the initiation of translation?
Which ribosomal site does the charged initiator tRNA enter during the initiation of translation?
Which of the following is TRUE about the initiation of translation in eukaryotes compared to bacteria?
Which of the following is TRUE about the initiation of translation in eukaryotes compared to bacteria?
What is the length of the Shine-Dalgarno sequence in the mRNA?
What is the length of the Shine-Dalgarno sequence in the mRNA?
What is the function of the ribosomal-binding site?
What is the function of the ribosomal-binding site?
What molecule facilitates the entry of a charged tRNA into the A site during translation elongation?
What molecule facilitates the entry of a charged tRNA into the A site during translation elongation?
Which ribosomal subunit is responsible for the formation of the peptidyl transferase activity?
Which ribosomal subunit is responsible for the formation of the peptidyl transferase activity?
What is the primary role of 16S rRNA in translation?
What is the primary role of 16S rRNA in translation?
What is the approximate rate of translation elongation in eukaryotes?
What is the approximate rate of translation elongation in eukaryotes?
Which of the following is NOT involved in the initiation of protein synthesis in eukaryotes?
Which of the following is NOT involved in the initiation of protein synthesis in eukaryotes?
What happens when a stop codon is encountered during translation?
What happens when a stop codon is encountered during translation?
Which of the following correctly describes the movement of the ribosome during translation elongation?
Which of the following correctly describes the movement of the ribosome during translation elongation?
What is the role of the 60S ribosomal subunit in translation elongation?
What is the role of the 60S ribosomal subunit in translation elongation?
Flashcards
Stop Codons
Stop Codons
Nonsense codons UAG, UAA, and UGA that signal termination of protein synthesis.
Release Factors
Release Factors
Proteins that recognize stop codons and promote termination of translation.
Bacterial Release Factors
Bacterial Release Factors
Three specific proteins in bacteria: RF1, RF2, and RF3 that recognize specific stop codons.
Eukaryotic Release Factor
Eukaryotic Release Factor
A single release factor (eRF) that recognizes all three stop codons in eukaryotes.
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Post-translational Modifications
Post-translational Modifications
Chemical changes after translation that enhance protein function and diversity.
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Central Dogma
Central Dogma
The process of genetic information flow: DNA to RNA to Protein.
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Eukaryotic Initiation Factors (eIF)
Eukaryotic Initiation Factors (eIF)
Proteins that bind to the 5' cap of mRNA and assist in translation initiation.
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80S initiation complex
80S initiation complex
The structure formed by the assembly of the 40S subunit, tRNAmet, and 60S subunit during translation initiation.
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Stages of Translation
Stages of Translation
Translation occurs in three stages: Initiation, Elongation, Termination.
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Translation elongation
Translation elongation
The stage in protein synthesis where amino acids are added to the growing polypeptide chain one by one.
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Initiation Complex
Initiation Complex
Formation of a complex involving mRNA, initiator tRNA, and ribosomal subunits.
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Start Codon
Start Codon
The codon in mRNA that signals the start of protein synthesis, typically AUG.
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Codon-anticodon recognition
Codon-anticodon recognition
The process by which the ribosome ensures correct pairing of tRNA and mRNA codons during translation.
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tRNAfmet
tRNAfmet
Initiator tRNA in bacteria that carries N-formylmethionine.
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Peptidyl transferase
Peptidyl transferase
An enzymatic function of ribosomal RNA that facilitates the formation of peptide bonds between amino acids.
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Translocation in translation
Translocation in translation
The movement of the ribosome along mRNA to position the next codon for translation.
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Shine-Dalgarno Sequence
Shine-Dalgarno Sequence
A ribosomal-binding site in bacterial mRNA that aligns with 16S rRNA.
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Initiation Factors
Initiation Factors
Proteins required to assist the formation of the initiation complex.
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EF-Tu
EF-Tu
A protein that facilitates the entry of charged tRNA into the A site of the ribosome.
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Differences in Eukaryotes
Differences in Eukaryotes
Eukaryotic translation initiation requires additional factors compared to bacteria.
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The Central Dogma: Translation of mRNA and Post-translational Modifications
- Translation occurs in three stages: initiation, elongation, and termination.
- Initiation involves the association of mRNA, initiator tRNA, and ribosomal subunits to form an initiation complex. Initiator tRNA recognizes the start codon (AUG, GUG, or UUG). In bacteria, this tRNA is tRNAfMet, carrying N-formylmethionine.
- The binding of mRNA to the 30S ribosomal subunit is aided by the Shine-Dalgarno sequence on mRNA which is complementary to a sequence in the 16S rRNA.
- IF3 promotes mRNA binding to the 30S subunit.
- IF2 promotes the binding of the initiator tRNA.
- The 50S ribosomal subunit joins.
- This forms the 70S initiation complex.
- Elongation involves adding amino acids to the polypeptide chain one at a time. This process is remarkably fast, ~15-18 amino acids per second in bacteria, and ~6 per second in eukaryotes.
- A charged tRNA binds to the A site.
- EF-Tu facilitates tRNA entry.
- Peptidyl transferase catalyzes bond formation between the polypeptide chain and the amino acid in the A site.
- The polypeptide is transferred to the A site.
- The ribosome translocates one codon to the right.
- Termination occurs when a stop codon (UAG, UAA, or UGA) is reached.
- Release factors (RFs) recognize the stop codons and facilitate the release of the polypeptide chain.
- Bacteria have three release factors: RF1 (recognizes UAA and UAG), RF2 (recognizes UAA and UGA), and RF3 (does not recognize any of the stop codons but helps to facilitate the termination process).
- Eukaryotes have one release factor (eRF).
- Release factors (RFs) recognize the stop codons and facilitate the release of the polypeptide chain.
Prokaryotic vs. Eukaryotic Translation
- Prokaryotic transcription and translation are simultaneous.
- Eukaryotic transcription and translation are discontinuous.
- Prokaryotic ribosomes are 70S (30S + 50S subunits). mRNAs are unstable, living for a few seconds to two minutes.
- Eukaryotic ribosomes are 80S (40S + 60S subunits). mRNAs are more stable, living for several hours to days. Transcription occurs in the nucleus, translation occurs in the cytoplasm.
- Initiation in prokaryotes involves three initiation factors (IFs), while initiation in eukaryotes involves nine initiation factors (eIFs).
- Prokaryotic initiation is cap-independent.
- Eukaryotic initiation is cap-dependent (and cap-independent in some cases).
Post-Translational Modifications (PTMs)
- Protein PTMs increase the functional diversity of the proteome.
- PTMs include phosphorylation, glycosylation, ubiquitination, nitrosylation, methylation, acetylation, lipidation, and proteolysis.
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