Genetic Code and Translation Quiz
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Questions and Answers

What is genetic code degeneracy?

  • Between 1 and 6 different codons code for a single amino acid (correct)
  • The replication of DNA
  • The process of synthesizing multiple proteins at once
  • Only one codon codes for an amino acid

    • What are the three major phases of Translation?

    Initiation, Elongation, Termination

    How does the ribosome find the start codon in the mRNA?

    The Shine-Dalgarno sequence

    What is the Shine-Dalgarno sequence?

    <p>It is complementary to an rRNA sequence in the 30S subunit.</p> Signup and view all the answers

    What role does the Shine-Dalgarno sequence play in translation initiation in prokaryotes?

    <p>It base-pairs with a portion of the 16S ribosomal RNA.</p> Signup and view all the answers

    What binds to the small ribosomal subunit during translation initiation in eukaryotes?

    <p>Initiation factors and an initiator tRNA charged with methionine.</p> Signup and view all the answers

    Which of the following states is true regarding the amino terminus of a polypeptide?

    <p>Encoded toward the 5' end of the mRNA</p> Signup and view all the answers

    What is the function of the Shine-Dalgarno sequence?

    <p>Specification of the authentic start codon</p> Signup and view all the answers

    Where is the Shine-Dalgarno sequence located?

    <p>Upstream of the AUG start codon on the mRNA.</p> Signup and view all the answers

    Which of the following is never found in the A-site of the ribosome?

    <p>Initiator tRNAmet</p> Signup and view all the answers

    What is the last component incorporated in the process of translational initiation?

    <p>Large ribosomal subunit</p> Signup and view all the answers

    What binds to an open A-site in the process of translational elongation?

    <p>Charged tRNA + elongation factor + GTP</p> Signup and view all the answers

    Which of the following base-pair interactions would not occur due to wobble?

    <p>U-C</p> Signup and view all the answers

    What is protein translocation?

    <p>The process where cytosolic ribosome begins translation and the signal peptide directs it to the ER.</p> Signup and view all the answers

    Study Notes

    Genetic Code Degeneracy and Decryption

    • Between 1 and 6 different codons can code for a single amino acid.
    • A single tRNA may recognize 2 to 3 different codons, leading to multiple distinct tRNAs for each amino acid.
    • Aminoacyl-tRNA synthetases (aaRS) are specific to each amino acid and must recognize multiple tRNAs.
    • Aminoacyl-tRNAs are crucial for translation accuracy, but the ribosome is unable to discriminate between correctly and incorrectly charged tRNAs.

    Phases of Translation

    • Translation consists of three major phases: Initiation, Elongation, and Termination.

    Shine-Dalgarno Sequence

    • The Shine-Dalgarno sequence helps the ribosome locate the start codon in mRNA.
    • It is complementary to a sequence in the 16S rRNA of the ribosomal 30S subunit.

    Translation Initiation in Prokaryotes

    • The Shine-Dalgarno sequence pairs with the 16S rRNA, located 5-10 nucleotides upstream of the start codon AUG.
    • The initiator tRNA charged with N-formyl methionine (fMet) pairs with the start codon, leading to the assembly of the large ribosomal subunit.

    Translation Initiation in Eukaryotes

    • Initiation factors bind to the small ribosomal subunit along with initiator tRNA charged with methionine.
    • The initiation complex interacts with the 5' cap before scanning the mRNA for the first AUG codon, triggering the assembly of the large ribosomal subunit.

    Importance of Translation Initiation

    • Proper initiation is crucial for in-frame translation.
    • In prokaryotes, mRNA binds to the small subunit via the Shine-Dalgarno sequence.
    • In eukaryotes, the small subunit scans from the 5' cap to the Kozak sequence's first AUG.

    Translation Elongation

    • Occurs similarly in prokaryotes and eukaryotes.
    • A charged aminoacyl-tRNA pairs with the mRNA at the A site, and peptide bonds form, extending the polypeptide chain.

    Role of Elongation Factors

    • In prokaryotes, elongation factor Tu (EF-Tu) delivers aminoacyl-tRNAs, while in eukaryotes, elongation factor 1A (EF1A) performs this task.
    • Elongation factor G (EF-G) in prokaryotes and elongation factor 2 (EF2) in eukaryotes provide energy for ribosomal translocation along mRNA, using GTP.

    Translation Termination

    • The process is similar in both prokaryotes and eukaryotes.
    • Release factors bind to stop codons (UAA, UAG, UGA) and are GTPases, facilitating polypeptide release and ribosome dissociation.

    Translation Directionality

    • The amino terminus of a polypeptide is encoded by the 5' end of mRNA, with translation proceeding in the 5' to 3' direction.

    Function of the Shine-Dalgarno Sequence

    • This sequence specifies the authentic start codon in bacterial mRNA and pairs with 16S rRNA for proper alignment.

    Location of the Shine-Dalgarno Sequence

    • It is found 3 to 9 nucleotides upstream of the AUG start codon on mRNA.

    A-site Occupancy

    • Initiator tRNAmet is never found in the A site; it is localized to the P site during initiation.

    Last Component in Translational Initiation

    • The large ribosomal subunit is the last component to enter during the initiation of translation in both bacteria and eukaryotes.

    A-site Binding During Elongation

    • An open A-site is occupied by a complex of charged tRNA, elongation factor, and GTP, leading to peptide bond formation.

    Wobble Base-Pairing

    • Wobble allows for imperfect pairing of the third base in codons, but U-C pairing does not occur as both are pyrimidines.

    Protein Translocation

    • Translation begins in the cytosol with the signal peptide signaling for SRP recognition, halting translation.
    • SRP binds to SR in the ER membrane, allowing translation to continue with the peptide entering the ER lumen.

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    Description

    Explore the concepts of genetic code degeneracy and its role in translation with this quiz. Test your understanding of codons, tRNAs, and the mechanisms that ensure translation accuracy. Whether you're reviewing for a class or expanding your knowledge, this quiz covers essential points in molecular biology.

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