Cell-Free Protein Synthesis
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Questions and Answers

What is the purpose of wobble pairing in translation?

  • To increase the accuracy of amino acid sequence
  • To reduce the number of tRNA molecules
  • To allow tRNA to recognize more than one codon (correct)
  • To ensure Watson-Crick base pairing
  • Which of the following codons can pair with a tRNA with anticodon 5' GCA 3'?

  • 5' GCC 3'
  • 5' GCG 3'
  • 5' GCU 3'
  • All of the above (correct)
  • What is the purpose of labelling phenylalanine with radioisotopes in a cell-free system?

  • To measure the concentration of amino acids
  • To detect the presence of ribosomes
  • To identify the start codon in a sequence
  • To trace the synthesis of proteins (correct)
  • How many tRNA molecules are necessary to recognize the 61 amino acid codons?

    <p>Less than 61</p> Signup and view all the answers

    What is the significance of the third position in a codon?

    <p>It is less critical and can vary</p> Signup and view all the answers

    What is the significance of the 'start codon' AUG?

    <p>It signals the start of translation and codes for methionine</p> Signup and view all the answers

    Which of the following tRNAs could be used in the translation of the codon 5' CUG 3'?

    <p>5' GAG 3'</p> Signup and view all the answers

    What is the consequence of the genetic code being read in triplets?

    <p>There are 64 codons that code for 20 amino acids</p> Signup and view all the answers

    What is the role of Har Gobind Khorana in deciphering the genetic code?

    <p>He developed a method to synthesize RNA with a specific sequence</p> Signup and view all the answers

    What is the result of wobble pairing in translation?

    <p>Increased efficiency of translation</p> Signup and view all the answers

    What is the consequence of the genetic code being degenerate?

    <p>There are multiple codons that code for a single amino acid</p> Signup and view all the answers

    Which of the following amino acids has only one codon?

    <p>Tryptophan</p> Signup and view all the answers

    What is the significance of reading frames in the genetic code?

    <p>They determine the grouping of triplets in a sequence</p> Signup and view all the answers

    What is the significance of the first two bases in a codon?

    <p>They are critical for Watson-Crick base pairing</p> Signup and view all the answers

    What was the limitation of Nirenberg's initial approach to deciphering the genetic code?

    <p>The sequence of nucleotides in RNA could not be controlled</p> Signup and view all the answers

    What was the outcome of Har Gobind Khorana's contribution to deciphering the genetic code?

    <p>All of the above</p> Signup and view all the answers

    What is the primary function of tRNAs during translation?

    <p>To link mRNA codons with specific amino acids</p> Signup and view all the answers

    How do prokaryotic ribosomes recognize the start codon during initiation?

    <p>By recognizing a specific sequence in the 5' UTR of the mRNA</p> Signup and view all the answers

    What is the role of EF-Tu GTP during elongation?

    <p>To facilitate the binding of aminoacyl tRNA to the ribosome</p> Signup and view all the answers

    What is the outcome of the peptidyl transferase process during elongation?

    <p>The formation of a peptide bond between two amino acids</p> Signup and view all the answers

    What is the role of IF1 and IF3 during prokaryotic translation initiation?

    <p>To bind the 30S subunit and recruit mRNA</p> Signup and view all the answers

    What is the result of the binding of the large 50S subunit to the ribosome during initiation?

    <p>The formation of the complete ribosome</p> Signup and view all the answers

    What is the purpose of wobble pairing during translation?

    <p>To allow a single tRNA anticodon to recognize more than one codon</p> Signup and view all the answers

    What is the function of aminoacyl-tRNA synthetases during translation?

    <p>To charge tRNAs with the correct amino acids</p> Signup and view all the answers

    What is the function of EF-G during prokaryotic translation?

    <p>To facilitate translocation of the ribosome with GTP hydrolysis</p> Signup and view all the answers

    What occurs at the A site during prokaryotic termination?

    <p>The release factor mimics the shape of a tRNA</p> Signup and view all the answers

    How do prokaryotes and eukaryotes differ in terms of transcription?

    <p>Prokaryotes transcribe in the cytoplasm, while eukaryotes transcribe in the nucleus</p> Signup and view all the answers

    What is the function of the release factor during prokaryotic termination?

    <p>To recognize the stop codon and terminate translation</p> Signup and view all the answers

    What is the difference between prokaryotic and eukaryotic mRNA?

    <p>Prokaryotic mRNA is polycistronic, while eukaryotic mRNA is monocistronic</p> Signup and view all the answers

    What is the outcome of peptide bond formation during elongation?

    <p>A peptide bond is formed between the incoming amino acid and the growing peptide</p> Signup and view all the answers

    What occurs during translocation of the ribosome?

    <p>The ribosome moves along the mRNA with GTP hydrolysis</p> Signup and view all the answers

    What is the fate of the discharged tRNA during prokaryotic elongation?

    <p>It is released from the E site</p> Signup and view all the answers

    What is the first step in the translation process in prokaryotic cells?

    <p>Binding of the 16S rRNA with the Shine-Dalgarno sequence</p> Signup and view all the answers

    What is the function of the large 50S subunit in the initiation of translation?

    <p>It binds to the initiation factors</p> Signup and view all the answers

    What is the site of protein synthesis in eukaryotic cells?

    <p>Bound to the rough endoplasmic reticulum</p> Signup and view all the answers

    What is the role of the initiator tRNA in the initiation of translation?

    <p>It carries the first amino acid to the ribosome</p> Signup and view all the answers

    How does the RNA differ from DNA?

    <p>RNA is single-stranded, contains U instead of A and ribose instead of deoxyribose</p> Signup and view all the answers

    What is the name of the sequence that the 16S rRNA binds to in the mRNA?

    <p>Shine-Dalgarno sequence</p> Signup and view all the answers

    What is the role of the 5' cap in the translation process?

    <p>It is not involved in the translation process</p> Signup and view all the answers

    Which of the following is not a type of RNA?

    <p>Polymerase RNA</p> Signup and view all the answers

    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.

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