Genetic Code and tRNA Overview
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Genetic Code and tRNA Overview

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Questions and Answers

What is the primary function of aminoacyl-tRNA synthase?

  • To synthesize amino acids
  • To facilitate protein folding
  • To attach amino acids to tRNAs (correct)
  • To degrade uncharged tRNAs

    • How many different aminoacyl-tRNA synthases are responsible for charging tRNAs?

  • 50
  • 20 (correct)
  • 10
  • 5

    • What energy source is required for the charging of tRNA?

  • ATP hydrolysis (correct)
  • NADH
  • GTP hydrolysis
  • FADH2

    • What does the specific recognition site of a tRNA provide?

    <p>Specificity for aminoacyl-tRNA synthetase</p> Signup and view all the answers

    What is produced as a result of the charging reaction of tRNA?

    <p>Charged tRNA (aminoacyl-tRNA)</p> Signup and view all the answers

    What molecule is released when an amino acid is attached to tRNA?

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

    What is the role of aminoacyl-tRNA synthetase in the process described?

    <p>To charge tRNA with an amino acid</p> Signup and view all the answers

    What happens to the tRNA after the amino acid is activated?

    <p>It becomes uncharged</p> Signup and view all the answers

    Which of the following correctly describes the initial binding process for tRNA?

    <p>A specific amino acid and ATP bind to aminoacyl-tRNA synthetase</p> Signup and view all the answers

    Which component is necessary for the covalent binding of an amino acid to tRNA?

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

    What does pyrophosphate consist of in this biochemical context?

    <p>Two phosphate groups</p> Signup and view all the answers

    In what circumstance is AMP released during the charging of tRNA?

    <p>After the covalent binding of an amino acid</p> Signup and view all the answers

    What is the state of the tRNA after being charged with an amino acid?

    <p>It is ready for translation</p> Signup and view all the answers

    What catalyzes the binding of the 50S rRNA subunit during initiation in prokaryotes?

    <p>Hydrolysis of GTP</p> Signup and view all the answers

    Which part of the mRNA is complementary to the Shine-Dalgarno sequence?

    <p>3'-16S rRNA</p> Signup and view all the answers

    What is the role of initiator tRNA during the initiation step in prokaryotic translation?

    <p>It binds the start codon AUG</p> Signup and view all the answers

    What occurs at the 3' end of a codon?

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

    Which elongation factor is responsible for recognizing and transporting aminoacyl-tRNAs to the A site?

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

    What is the result of the arrangement of hydrogen bonds at the third position of the codon-anticodon pair?

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

    During elongation, what is found in the P site of the ribosome?

    <p>Peptidyl-tRNA</p> Signup and view all the answers

    What structural feature aids in amino acid binding in tRNA?

    <p>Cloverleaf structure</p> Signup and view all the answers

    What happens to EF-Tu after it delivers the aminoacyl-tRNA to the ribosome?

    <p>It is recycled for future use</p> Signup and view all the answers

    Which sites are found in the structure of a ribosome during protein synthesis?

    <p>P site and A site</p> Signup and view all the answers

    What is the result of IF3 being removed during the initiation phase?

    <p>It allows protein synthesis to begin</p> Signup and view all the answers

    What does the term 'degeneracy of the code' refer to?

    <p>Same amino acid coded by multiple codons</p> Signup and view all the answers

    Which of the following correctly describes the state of the ribosome during the initiation phase?

    <p>70S initiation complex is formed</p> Signup and view all the answers

    Which characteristic is NOT a feature of tRNA?

    <p>Peptidyl site</p> Signup and view all the answers

    Which type of bond is crucial for stabilizing the structure of tRNA?

    <p>Hydrogen bonds</p> Signup and view all the answers

    How many tRNAs are needed to read the complete set of codons?

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

    Which direction does the amino acid attachment site of tRNA point?

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

    Which mechanism allows tRNA to correspond to different amino acids?

    <p>Wobble hypothesis</p> Signup and view all the answers

    What occurs during the initiation phase of translation?

    <p>The ribosome assembles at the correct site on mRNA with initiation factors.</p> Signup and view all the answers

    What role does tRNA play during the elongation phase?

    <p>It brings the correct amino acid to the ribosome.</p> Signup and view all the answers

    What distinguishes prokaryotic translation from eukaryotic translation?

    <p>Prokaryotes use a Shine-Dalgarno sequence for initiation.</p> Signup and view all the answers

    In eukaryotic translation, what is the Kozak sequence associated with?

    <p>It assists with the binding of the ribosome to the mRNA.</p> Signup and view all the answers

    What happens when a stop codon is reached during translation?

    <p>The ribosome dissociates and releases the polypeptide.</p> Signup and view all the answers

    Which molecule is bound by IF2 during the process of translation initiation?

    <p>The initiating tRNA.</p> Signup and view all the answers

    What is the primary function of initiation factors in prokaryotic translation?

    <p>To ensure correct binding and prevent errors in initiation.</p> Signup and view all the answers

    What is the role of formyl-methionine in prokaryotic translation initiation?

    <p>It is the first amino acid incorporated into the growing polypeptide chain.</p> Signup and view all the answers

    Study Notes

    The Wobble

    • The wobble occurs at the 3’ end of the codon and 5’ end of the anti-codon.
    • The wobble is a result of the arrangement of hydrogen bonds of base pairs at the third position of the codon.
    • The degeneracy of the genetic code allows for the wobble to always result in the translation of the same amino acid.
    • A complete set of codons can be read by fewer than 61 tRNAs.

    tRNA

    • tRNA molecules carry specific amino acids to the ribosome.
    • tRNA molecules are encoded by different genes.
    • There are 20 aminoacyl-tRNA synthases which "charge" the tRNA molecules.
    • All tRNA molecules possess specific aa-tRNA synthetase recognition sites.
    • tRNA molecules have a cloverleaf structure with an acceptor stem and an anticodon loop that binds to the mRNA codon.

    Ribosomes

    • The overall ribosome shape is determined by rRNA.
    • Ribosomes are discrete in size.
    • Ribosomes have two sites:
      • P site (peptidyl site)
      • A site (aminoacyl site)
    • Ribosomes are essential for polypeptide synthesis.

    Step 1- Charging of tRNA (aminoacylation)

    • Amino acids are attached to tRNAs by aminoacyl-tRNA synthetase.
    • There are 20 aminoacyl-tRNA synthases capable of charging all tRNAs.
    • tRNA molecules possess specific aa-tRNA synthetase recognition sites.
    • The process uses energy derived from ATP hydrolysis.
    • This results in a charged tRNA called aminoacyl-tRNA.

    Initiation, Elongation and Termination

    • Initiation:
      • This stage involves assembly of a functional ribosome in the correct location on the mRNA molecule.
      • The assembled ribosome is ready to begin protein synthesis.
    • Elongation:
      • tRNA molecules bring the correct amino acid to the ribosome.
      • The amino acid is joined to the growing polypeptide chain.
      • The ribosome moves to the next codon on the mRNA.
    • Termination:
      • This stage is triggered by the ribosome reaching a stop codon.
      • The entire complex disassembles, releasing the newly synthesized polypeptide.

    Prokaryotic vs Eukaryotic Translation

    • Prokaryotes:
      • Translation occurs in the cytoplasm.
      • Transcription and translation occur simultaneously.
      • Translation begins at Shine-Dalgarno sequences.
      • The initiating tRNA is formyl-methionine.
    • Eukaryotes:
      • Translation occurs in the cytoplasm.
      • Transcription and translation occur separately.
      • Translation begins at the AUG codon, which is embedded in a short initiation sequence called the Kozak sequence.
      • The initiating tRNA is methionine.

    Initiation (Prokaryotes)

    • Binding of 30S subunit and initiation factors:
      • Initiation factor 1 (IF1) associates with the 30S subunit in the A site, blocking tRNA entry.
      • Initiation factor 3 (IF3) allows the 30S subunit to bind to the specific site on the mRNA.
      • Initiation factor 2 (IF2) binds to the 30S P site, facilitating the binding of formylmethionine tRNA (fMet-tRNA) to IF2.
      • IF2 moves fMet-tRNA to the P site.
      • Hydrolysis of GTP occurs following the arrival of the 50S subunit, leading to a conformational change and forming a 70S ribosome.

    Step 2- Initiation Steps (Prokaryotes)

    • The Shine-Dalgarno sequence is complementary to the 3’ end of the 16S rRNA.
    • The initiator tRNA (fMet tRNA) binds to the AUG start codon on the mRNA.
    • IF3 is removed and recycled.
    • IF1 and IF2 are released, and GTP is hydrolyzed, leading to the binding of the 50S rRNA subunit.
    • This results in a 70S initiation complex comprising of mRNA, 70S ribosome, and fMet-tRNA.

    Elongation

    • The A site is empty.
    • The P site contains the peptidyl tRNA.
    • The E site contains an uncharged tRNA.
    • Elongation requires elongation factors (EF-Tu, EF-Ts, and EF-G).
    • EF-Tu-GTP: Recognizes and transports aminoacyl-tRNA to the A site of the ribosome.
    • EF-Tu is released from the ribosome after GTP hydrolysis to GDP.

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    Description

    Explore the fascinating concepts of wobble base pairing, the structure and function of tRNA molecules, and the role of ribosomes in protein synthesis. This quiz covers important aspects such as the degeneracy of the genetic code and the specific recognition sites on tRNA. Test your knowledge on these fundamental topics in molecular biology.

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