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Genetics: Translation of mRNA

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Termini in questo insieme (27)

  • One gene-one enzyme hypothesis
    A single gene controls the synthesis of a single enzyme. Modifications include that enzymes are one protein category, some proteins have multiple polypeptides, some genes code for functional RNAs, and one gene can code for multiple polypeptides.
  • Genetic code
    The set of rules by which information encoded in mRNA codons is translated into amino acids in proteins. It uses triplet codons, start codon AUG, and stop codons UAA, UAG, UGA.
  • Degeneracy of the genetic code
    Multiple codons can specify the same amino acid, e.g., GGU, GGC, GGA, and GGG all code for glycine. These are called synonymous codons.
  • Exceptions to the genetic code
    Selenocysteine (Sec) and pyrrolysine (Pyl) are rare amino acids coded by UGA and UAG codons, respectively, requiring special tRNAs and mRNA sequences.
  • Reading frame
    The series of codons in mRNA starting with the start codon. A frameshift mutation changes the reading frame, altering the entire downstream amino acid sequence.
  • Directionality of polypeptide synthesis
    Polypeptides are synthesized from the amino (N) terminus to the carboxyl (C) terminus, while mRNA is read 5-prime to 3-prime.
  • Levels of protein structure
    Primary: amino acid sequence; Secondary: alpha helices and beta sheets; Tertiary: 3D folding; Quaternary: multiple polypeptides forming a complex.
  • Functions of proteins
    Proteins perform transport, movement, cell shape, signaling, surface recognition, and enzymatic catalysis.
  • Aminoacyl-tRNA synthetases
    Enzymes that attach specific amino acids to their corresponding tRNAs, producing charged tRNAs for translation.
  • Wobble hypothesis
    The third base of the codon can tolerate certain mismatches with the anticodon, allowing fewer tRNAs to recognize multiple codons.
  • Ribosome structure
    Composed of large and small subunits made of rRNA and proteins; bacterial ribosomes are 70S (30S + 50S), eukaryotic are 80S (40S + 60S).
  • Sites in the ribosome
    Three sites: E (exit), P (peptidyl), and A (aminoacyl) where tRNAs bind during translation.
  • Initiation of translation in bacteria
    Initiator tRNA (fMet-tRNA) binds start codon AUG with help of initiation factors IF1, IF2, IF3 and Shine-Dalgarno sequence aligns mRNA on 30S subunit.
  • Initiation of translation in eukaryotes
    Initiation complex forms with eIFs, 40S subunit, and tRNA-met; binds 5-prime cap and scans for AUG within Kozak sequence before 60S subunit joins.
  • Elongation stage of translation
    Charged tRNA enters A site, peptide bond forms transferring polypeptide to A site tRNA, ribosome translocates moving tRNAs through E, P, and A sites.
  • Termination of translation
    Stop codons are recognized by release factors (RFs), which promote release of the polypeptide and dissociation of the ribosome.
  • Coupling of transcription and translation
    In bacteria, translation begins on mRNA before transcription finishes due to lack of nucleus; this does not occur in eukaryotes.
  • Antibiotics affecting translation
    Examples include chloramphenicol (blocks peptidyl transferase), erythromycin (blocks translocation), puromycin (causes premature release), tetracycline (blocks tRNA binding), and streptomycin (causes misreading).
  • Structure of tRNA
    tRNAs have a cloverleaf secondary structure with an anticodon loop that pairs with mRNA codons and a 3-prime CCA end where the amino acid attaches.
  • Charging of tRNAs
    Aminoacyl-tRNA synthetases catalyze attachment of amino acids to tRNAs in a two-step reaction using ATP, producing charged tRNAs for translation.
  • Shine-Dalgarno sequence
    A ribosomal binding site in bacterial mRNA complementary to 16S rRNA that helps position the mRNA for translation initiation.
  • Kozak sequence
    A consensus sequence around the start codon in eukaryotic mRNAs that facilitates recognition of the correct AUG for translation initiation.
  • Decoding function of the ribosome
    The 16S rRNA monitors correct codon-anticodon pairing at the A site and prevents elongation if an incorrect tRNA is bound.
  • Peptidyl transferase activity
    Catalyzed by 23S rRNA in the large ribosomal subunit, it forms peptide bonds between amino acids during elongation.
  • Triplet-binding assay
    An experimental method to identify which RNA triplets bind specific tRNAs carrying amino acids, helping decipher the genetic code.
  • RNA copolymers in genetic code research
    Synthetic RNAs with repeating sequences were used in cell-free systems to identify codons corresponding to specific amino acids.
  • Differences in translation among domains
    Bacteria use fMet-tRNA and Shine-Dalgarno sequences; archaea and eukaryotes use Met-tRNA and different initiation factors; eukaryotes require 5-prime cap recognition.