Module 7: From RNA to protein

• The genetic code is degenerate, meaning there are multiple codons that code for the same amino acid.
• Degeneracy in the genetic code allows for the creation of proteins with different sequences from the same gene.
• The genetic code was broken by Marshall Nirenberg, Francis Crick, George Gamow, Har Gobind Khorana, Philip Leder.
• The Nirenberg-Matthaei experiment involved bacterial extract competent for translation, 19 amino acids, and 1 labelled amino acid.
• In the Nirenberg-Matthaei experiment, only labelled phe gave a labelled polypeptide.
• The sequence of codons that runs from a specific start codon to a specific stop codon is an open reading frame.
• Almost every protein chain initiates with AUG, which codes for Methionine.
• There are 3 stop codons UAA, UGA, and UAG that do not specify amino acids.
• Aminoacyl-tRNA synthetases each recognize only one of 20 aminoacyl-tRNA synthetases.
• Each tRNA is recognised by only one of 20 aminoacyl-tRNA synthetases, ensuring proofreading.
• Wobble base pairing allows unconventional base pairing between the third base in a codon and the first base in an anticodon, permitting degeneracy in the genetic code.
• tRNA function = link specific amino acids and recognise a codon in mRNA- ensures amino acid-codon match
• mRNA is used to code for a polypeptide chain.
• Translation involves three stages: Initiation, Elongation, and Termination.
• The ribosome is a RNA/protein complex composed of two subunits: the Small subunit and the Large subunit.
• Translation cofactors are essential for the roles of the ribosome in translation.
• The initiation, elongation, and termination of translation are processes that involve the ribosome.
• Nucleotide triphosphates play important roles in translation.
• The ribosome plays a crucial role in translation and in translation start site selection.
• rRNA’s have elaborate secondary structures made up of 40 or more stem loops.
• The 30S subunit of E. coli, showing examples of 16S rRNA helices from a biochemically derived model, is an example of ribosome structure.
• The ribosome illustration shows the position of a tRNA in the A-site within the 70S ribosome in its pre-translocational state.
• Attachment of amino acids to tRNA 3’ “acceptor arm” is a two step process: AA + ATP  AA-AMP + PP and AA-AMP + tRNA  AA-tRNA + AMP.
• The Shine-Dalgarno sequence, also known as Kozak sequence in eukaryotes, is a conserved sequence that interacts with 16S rRNA of the 30S small subunit to identify the site of initiation of protein synthesis.
• Termination factors RF1 recognize UAA/UAG, RF2 recognize UAA/UGA, and RF3 helps RF1 or 2 bind to ribosome.
• GTP is involved in protein synthesis during the initiation stage, when the large subunit is added.
• Initiation factors IF2 tag tRNAi and regulate entry into ribosome.
• GTP is involved in protein synthesis during the peptide synthesis and translocation stage.
• GTP is involved in protein synthesis during the termination stage, when the peptide chain is released and the ribosome dissociates.
• Elongation factors EF-GTP bind to A site when termination codon appears.
• Elongation factors EF-G mediate translocation.
• GTP is involved in protein synthesis during the elongation stage, when aminoacyl-tRNA is added by EF-Tu.
• GTP provides energy for protein synthesis.
• Elongation factors EF-Tu mediate aminoacyl-tRNA entry to ribosome.
• Initiation factors IF1 blocks A site to tRNAi-met, inhibiting premature 30S-50S interaction.
• Initiation factors IF3 inhibit premature 30S-50S interaction and stabilise free 30S.
• In prokaryotes, two tRNA’s are used for methionine, one for initiation (tRNA i), one for elongation.
• Prokaryotic initiating met is formylated (fmet).
• Initiation of translation involves finding the right codon.