Cell-Free Protein Synthesis Experiment
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Questions and Answers

What is the primary advantage of synthesizing RNA with a specific sequence in deciphering the genetic code?

  • It allows for the creation of multiple reading frames
  • It enables the control of nucleotide polymerization order
  • It increases the chances of obtaining a start codon
  • It facilitates the assignment of codons to amino acids (correct)

    • What is the outcome when a tube containing labelled phenylalanine has a high signal above background?

  • Phenylalanine is the only amino acid radio-labelled (correct)
  • All amino acids are radio-labelled equally
  • Ribosomes are not stuck to the filter paper
  • Only serine and leucine are radio-labelled

    • What is the purpose of the anticodon on the tRNA molecule?

  • To recognize the start codon during translation
  • To release the amino acid from the ribosome
  • To bind to the mRNA codon during translation (correct)
  • To provide the sequence for protein synthesis

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

    <p>64 codons are possible, but only 20 amino acids can be encoded</p> Signup and view all the answers

    What is the purpose of the 'start codon' in the genetic code?

    <p>To signal the start of translation and specify the first amino acid</p> Signup and view all the answers

    Why is it important to consider reading frames when deciphering the genetic code?

    <p>Because it determines which triplets are produced</p> Signup and view all the answers

    What is the significance of the 'stop codons' in the genetic code?

    <p>They signal the termination of translation and the end of the protein</p> Signup and view all the answers

    What was the main challenge faced by Nirenberg's lab initially?

    <p>Controlling the order of nucleotide polymerization</p> Signup and view all the answers

    What is the consequence of the genetic code being degenerate?

    <p>More than one codon can encode the same amino acid</p> Signup and view all the answers

    What is the purpose of wobble pairing in translation?

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

    Which of the following amino acids is encoded by a single codon?

    <p>Both b and c</p> Signup and view all the answers

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

    <p>They are always the same for a particular amino acid</p> Signup and view all the answers

    Which of the following is a consequence of wobble pairing?

    <p>More than one codon can be recognized by a single tRNA species</p> Signup and view all the answers

    Which of the following anticodons could pair with the codon 5’ CUG 3’?

    <p>5’ GAG 3’</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 follow non-Watson-Crick base pairing</p> Signup and view all the answers

    Which of the following codons could pair with a tRNA with anticodon 5’ GCA 3’?

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

    What is the consequence of having fewer than 61 tRNA molecules?

    <p>Some tRNA molecules must recognize more than one codon</p> Signup and view all the answers

    What is the function of the anticodon in the central loop of tRNA?

    <p>to pair with an mRNA codon during translation</p> Signup and view all the answers

    What is the purpose of wobble pairing in translation?

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

    Which of the following is NOT a part of the initiation complex in prokaryotic translation?

    <p>50S subunit</p> Signup and view all the answers

    What is the purpose of the Shine-Dalgarno sequence in prokaryotic translation?

    <p>to line up the fMet-tRNAfMet with the start codon</p> Signup and view all the answers

    During elongation, what happens to EF-Tu after GTP hydrolysis?

    <p>it becomes EF-Tu GDP</p> Signup and view all the answers

    What is the net result of 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 function of aminoacyl-tRNA synthetases?

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

    What is the analogous process in translation to building a wall by adding bricks?

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

    What is the result of combining 30S and 50S ribosomal subunits?

    <p>70S ribosome</p> Signup and view all the answers

    Where can polyribosomes be found in a cell?

    <p>Either in the cytoplasm or bound to rough endoplasmic reticulum</p> Signup and view all the answers

    What is responsible for positioning the ribosome at the start codon?

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

    What is the initiator tRNA in eukaryotic cells?

    <p>met-tRNAmet</p> Signup and view all the answers

    What is the role of initiation factors during translation initiation?

    <p>To hydrolyze GTP and bind the large 50S subunit</p> Signup and view all the answers

    During which stage of translation is the nascent polypeptide synthesized?

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

    What is the function of a release factor during translation?

    <p>To terminate translation</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 was deciphered using synthetic mRNA and evaluating which amino acids were incorporated
    • Amino acids are encoded by triplets of nucleotide bases (codons)
    • The code is degenerate – most amino acids are coded for by more than one codon
    • One start codon (AUG) and three stop codons
    • Where you begin to read the code will determine which triplets are produced
    • Each possible grouping of triplets is called a ‘reading frame’

    Translation: Requirements and Components

    • RNA required for translation:
      • mRNA (encodes proteins)
      • tRNA (delivers amino acids to the ribosome)
      • rRNA (structural and enzymatic component of the ribosome)
    • Ribosomes are required for translation

    Translation: tRNA Molecule

    • tRNA is the adaptor molecule that links an mRNA codon with a specific amino acid
    • tRNA molecule:
      • 75-90 nucleotides
      • Extensive internal base pairing
      • Clover leaf structure
      • Contains unusual bases
      • CCA-OH sequence at 3’ end
      • Anticodon on central loop
    • Anticodon:
      • A triplet of bases that are complementary to the codon
      • These bases are unpaired and available for hydrogen bonding

    Translation: Wobble Mechanism

    • Wobble pairing allows a single tRNA anticodon to recognize more than one codon
    • Often the first two letters in the codon are the same, and the third base can vary
    • Third position less critical and can follow non-Watson-Crick base pairing between mRNA and tRNA

    Translation: Initiation, Elongation, and Termination

    • Initiation:
      • Requires initiation factors (IFs)
      • fMet-tRNAfMet in complex with IF2-GTP
      • Hydrolysis of GTP accompanied by the binding of the large 50S subunit
      • 16S rRNA binds the Shine-Dalgarno sequence in the mRNA to line up fMet-tRNAfMet with AUG start codon
    • Elongation:
      • Next aminoacyl tRNA binds to elongation factor EF-Tu GTP and enters A site in the ribosome
      • If the anticodon of the incoming tRNA is complementary to the codon, then hydrolysis of GTP takes place, and EF-Tu GDP + Pi are released
      • Peptidyl transferase process: the wall is built by lifting the incomplete wall, and placing the new brick underneath
    • Termination:
      • Requires a release factor that mimics the shape of a tRNA

    Differences between Prokaryotic and Eukaryotic Translation

    • Key differences between prokaryotic and eukaryotic translation

    Learning Outcomes

    • Recap of 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 assesses understanding of a cell-free system experiment involving ribosomes, amino acids, and filter paper to measure protein synthesis. It tests knowledge of how to identify radio-labelled amino acids in a tube.

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