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Questions and Answers
What is the purpose of wobble pairing in translation?
What is the purpose of wobble pairing in translation?
Which of the following codons can pair with a tRNA with anticodon 5' GCA 3'?
Which of the following codons can pair with a tRNA with anticodon 5' GCA 3'?
What is the purpose of labelling phenylalanine with radioisotopes in a cell-free system?
What is the purpose of labelling phenylalanine with radioisotopes in a cell-free system?
How many tRNA molecules are necessary to recognize the 61 amino acid codons?
How many tRNA molecules are necessary to recognize the 61 amino acid codons?
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What is the significance of the third position in a codon?
What is the significance of the third position in a codon?
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What is the significance of the 'start codon' AUG?
What is the significance of the 'start codon' AUG?
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Which of the following tRNAs could be used in the translation of the codon 5' CUG 3'?
Which of the following tRNAs could be used in the translation of the codon 5' CUG 3'?
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What is the consequence of the genetic code being read in triplets?
What is the consequence of the genetic code being read in triplets?
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What is the role of Har Gobind Khorana in deciphering the genetic code?
What is the role of Har Gobind Khorana in deciphering the genetic code?
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What is the result of wobble pairing in translation?
What is the result of wobble pairing in translation?
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What is the consequence of the genetic code being degenerate?
What is the consequence of the genetic code being degenerate?
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Which of the following amino acids has only one codon?
Which of the following amino acids has only one codon?
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What is the significance of reading frames in the genetic code?
What is the significance of reading frames in the genetic code?
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What is the significance of the first two bases in a codon?
What is the significance of the first two bases in a codon?
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What was the limitation of Nirenberg's initial approach to deciphering the genetic code?
What was the limitation of Nirenberg's initial approach to deciphering the genetic code?
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What was the outcome of Har Gobind Khorana's contribution to deciphering the genetic code?
What was the outcome of Har Gobind Khorana's contribution to deciphering the genetic code?
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What is the primary function of tRNAs during translation?
What is the primary function of tRNAs during translation?
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How do prokaryotic ribosomes recognize the start codon during initiation?
How do prokaryotic ribosomes recognize the start codon during initiation?
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What is the role of EF-Tu GTP during elongation?
What is the role of EF-Tu GTP during elongation?
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What is the outcome of the peptidyl transferase process during elongation?
What is the outcome of the peptidyl transferase process during elongation?
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What is the role of IF1 and IF3 during prokaryotic translation initiation?
What is the role of IF1 and IF3 during prokaryotic translation initiation?
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What is the result of the binding of the large 50S subunit to the ribosome during initiation?
What is the result of the binding of the large 50S subunit to the ribosome during initiation?
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What is the purpose of wobble pairing during translation?
What is the purpose of wobble pairing during translation?
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What is the function of aminoacyl-tRNA synthetases during translation?
What is the function of aminoacyl-tRNA synthetases during translation?
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What is the function of EF-G during prokaryotic translation?
What is the function of EF-G during prokaryotic translation?
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What occurs at the A site during prokaryotic termination?
What occurs at the A site during prokaryotic termination?
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How do prokaryotes and eukaryotes differ in terms of transcription?
How do prokaryotes and eukaryotes differ in terms of transcription?
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What is the function of the release factor during prokaryotic termination?
What is the function of the release factor during prokaryotic termination?
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What is the difference between prokaryotic and eukaryotic mRNA?
What is the difference between prokaryotic and eukaryotic mRNA?
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What is the outcome of peptide bond formation during elongation?
What is the outcome of peptide bond formation during elongation?
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What occurs during translocation of the ribosome?
What occurs during translocation of the ribosome?
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What is the fate of the discharged tRNA during prokaryotic elongation?
What is the fate of the discharged tRNA during prokaryotic elongation?
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What is the first step in the translation process in prokaryotic cells?
What is the first step in the translation process in prokaryotic cells?
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What is the function of the large 50S subunit in the initiation of translation?
What is the function of the large 50S subunit in the initiation of translation?
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What is the site of protein synthesis in eukaryotic cells?
What is the site of protein synthesis in eukaryotic cells?
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What is the role of the initiator tRNA in the initiation of translation?
What is the role of the initiator tRNA in the initiation of translation?
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How does the RNA differ from DNA?
How does the RNA differ from DNA?
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What is the name of the sequence that the 16S rRNA binds to in the mRNA?
What is the name of the sequence that the 16S rRNA binds to in the mRNA?
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What is the role of the 5' cap in the translation process?
What is the role of the 5' cap in the translation process?
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Which of the following is not a type of RNA?
Which of the following is not a type of RNA?
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Study Notes
Deciphering the Genetic Code
- The genetic code is read in triplets, with 64 codons encoding 20 amino acids.
- The code is degenerate, with multiple codons coding for the same amino acid.
- One 'start codon' (AUG) signals the start of translation, and all proteins start with a methionine (Met).
- Three 'stop codons' signal the termination of translation/end of protein.
Reading Frames
- The genetic code can be read in different triplets, depending on the starting point.
- Different reading frames produce different triplets, and each possible grouping is called a 'reading frame'.
Deciphering the Genetic Code - Historical Context
- Initially, Nirenberg's lab couldn't control the order of nucleotide polymerization.
- Har Gobind Khorana worked out how to synthesize RNA with a specific sequence, making it easier to assign codons to amino acids.
- Khorana shared the 1968 Nobel Prize with Nirenberg and Robert W. Holley for deciphering the genetic code.
Translation: Wobble Mechanism
- 61 amino acid codons, but less than 61 tRNA molecules, mean some tRNAs must recognize more than one codon.
- 'Wobble pairing' allows a single tRNA to recognize more than one codon.
- Often, the first two letters in a codon are the same, and the third base can vary.
- Third position is less critical and can follow non-Watson-Crick base pairing between mRNA and tRNA.
Translation: Components
- RNA and ribosomes are required for translation.
- Transfer RNAs (tRNAs) function as adaptors, linking mRNA codons with specific amino acids.
- Amino acids are attached to the 3' end of tRNA via an ester linkage.
- The central loop of tRNA contains an anticodon, which can pair with an mRNA codon.
Prokaryotic Translation: Initiation
- Initiation factors (IFs) IF1 and IF3 bind to the 30S subunit.
- This complex binds mRNA, and fMet-tRNAfMet in complex with IF2-GTP enters the P site.
- 16S rRNA binds to the Shine-Dalgarno sequence in the mRNA to line up fMet-tRNAfMet with the AUG start codon.
Prokaryotic Translation: Elongation
- Next aminoacyl tRNA binds to elongation factor EF-Tu GTP and enters the A site.
- If the anticodon of the incoming tRNA is complementary to the codon, hydrolysis of GTP takes place, and EF-Tu GDP + Pi are released.
- The protein is synthesized by 'lifting' the incomplete polypeptide and placing the incoming amino acid underneath.
Prokaryotic Translation: Termination
- Stop codon (UAA, UAG, or UGA) is presented in the A site.
- Release factor (RF1 or RF2) mimics the shape of a tRNA and enters the A site with a H2O molecule.
- Peptide is hydrolyzed from the final tRNA using the H2O molecule.
Prokaryotes vs Eukaryotes
- Prokaryotes: transcription occurs in the cytoplasm, polycistronic mRNA, and 30S + 50S = 70S ribosome.
- Eukaryotes: transcription occurs in the nucleus, monocistronic mRNA, and 40S + 60S = 80S ribosome.
- Initiation requires different mechanisms, including the interaction of 16S rRNA with the Shine-Dalgarno sequence in prokaryotes and the 5' cap interacting with the ribosome in eukaryotes.
Learning Outcomes
- Outline how the genetic code was deciphered.
- Explain how amino acids are encoded by groups of three nucleotide bases.
- Describe the components required for translation.
- Outline the process of activation of an amino acid to form an amino acyl tRNA.
- Describe the 3 stages of translation in prokaryotic cells.
- Identify ways in which eukaryotic translation differs from prokaryotic translation.
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Description
This quiz covers the process of cell-free protein synthesis, including the use of ribosomes, amino acids, and radiolabeling. It tests your understanding of how protein synthesis occurs in a cell-free system.