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tRNAs, the Genetic Code, and Translation in General Biology

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  • What is a codon?

    A codon is a 3-letter sequence of mRNA read 5’ to 3’ that corresponds to one amino acid or a stop signal during translation.

  • What is the start codon and what amino acid does it code for?

    The start codon is 5’AUG3’ and it codes for methionine, which is the first amino acid in protein synthesis.

  • What are the stop codons in mRNA?

    The stop codons are 5’UAA3’, 5’UGA3’, and 5’UAG3’. They signal termination of translation.

  • What is the anticodon and how does it pair with the codon?

    The anticodon is a 3-nucleotide sequence on tRNA that pairs antiparallel and complementary to the mRNA codon during translation.

  • What stabilizes the secondary structure of tRNA?

    tRNA folds into a complex secondary structure stabilized by intramolecular hydrogen bonds (base pairing within the same molecule).

  • What is the significance of the 5’CCA3’ sequence on tRNA?

    The 5’CCA3’ sequence at the amino acid end of tRNA is added after transcription and is the site where the amino acid attaches.

  • What is the role of aminoacyl-tRNA synthetases?

    Aminoacyl-tRNA synthetases charge tRNAs by attaching the correct amino acid to its corresponding tRNA using ATP.

  • Explain the wobble base pairing rule.

    The wobble base pairing allows flexibility in pairing between the 5’ anticodon position of tRNA and the 3’ codon position of mRNA, enabling one tRNA to recognize multiple codons.

  • What base in the anticodon can pair with multiple codon bases in wobble pairing?

    Inosine (I) in the 5’ position of the anticodon can pair with U, C, or A in the codon, increasing codon recognition flexibility.

  • How many reading frames are possible in double-stranded DNA?

    There are 6 possible reading frames in double-stranded DNA: 3 on each strand read 5’ to 3’.

  • What defines an open reading frame (ORF)?

    An ORF is a sequence from a start codon to an in-frame stop codon that potentially encodes a protein.

  • What is the role of the 5’ untranslated region (5’ UTR) in mRNA?

    The 5’ UTR contains regulatory sequences that help ribosomes bind and initiate translation at the correct start codon.

  • What is the ribosome binding site in bacterial mRNA?

    The ribosome binding site is part of the 5’ UTR and aligns the start codon with the ribosome's P site for translation initiation.

  • What are the three phases of translation?

    The three phases are initiation, elongation, and termination.

  • What energy source powers the peptide bond formation during translation elongation?

    The energy comes from the high-energy bond between the amino acid and tRNA formed during charging, not from GTP hydrolysis.

  • How do antibiotics like tetracycline inhibit translation?

    Tetracycline blocks the A site of bacterial ribosomes, preventing elongation by stopping aminoacyl-tRNA entry.

  • What is the effect of the toxin ricin on ribosomes?

    Ricin removes a specific adenine from ribosomal RNA in the large subunit, halting protein synthesis and killing the cell.

  • What is the difference between bound and free ribosomes?

    Bound ribosomes are attached to the ER and translate membrane or secreted proteins; free ribosomes translate cytosolic proteins. Ribosomes can switch based on signal sequences.

  • What is the role of release factors in translation?

    Release factors recognize stop codons and promote termination by releasing the newly made polypeptide from the ribosome.

  • How can ribosome poisons be used to measure protein half-life?

    By blocking new protein synthesis with a ribosome poison and measuring protein levels over time (e.g., via Western blot), the natural degradation rate (half-life) can be determined.