BABS1201 Lecture Notes - Lecture 12: Chloramphenicol, Rifampicin, Release Factor
28 May 2018
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Gene Expression II - translation
Overview of translation
• Ribosome - site of protein synthesis / translation
o Positions molecules in the right position
• tRNA - carries an amino acid and anti-codon
o Moves into the ribosome
o Anticodon base pairs with mRNA
o Places amino acids in the correct sequence
tRNA (transfer RNA)
• RNA
o Single-stranded
o Lot of intramolecular hydrogen bonding
o Ribose backbone
• Forms H bonds within itself - causes it to twist
• Amino acid attaches to 3' end
• Anticodon - on the other end (will base-pair with codon sequence of mRNA)
o There is a tRNA for every amino acid
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Aminoacyl-tRNA synthase
• Enzyme that synthesises a specific amino acid to tRNA
• Binds to amino acid
o Uses ATP (adenosine-P)
o Forms high energy bond
• Two high energy bonds are broken
o One high energy bond still attached to amino acid
o Releases two phosphate ions
• Binds to correct tRNA
o tRNA replaces adenosine
▪ AMP is released
o Does not require additional ATP
• Releases 'activated amino acid' (aminoacyl tRNA)
Translation
• Ribosome
o Site of protein synthesis
o Composed of two subunits
o Has sites for binding tRNAs
▪ A site - for aminoacyl-tRNAs (tRNA containing amino acid)
▪ P site - for peptidyl-tRNAs (tRNA holding peptide chain)
▪ E site - exit site (for tRNA that does not hold anything)
o Incoming tRNA enters the large subunit
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• Initiation
• The small subunit binds to:
o mRNA
o Initiator tRNA
▪ Modified base of mRNA helps ribosome read the RNA
▪ Start codon - located within the RNA
• Sets the reading frame (3 nucleotides at a time from the start codon)
o Large subunit
▪ Binds with the initiator tRNA in the P site
▪ Requires energy (GTP)
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Document Summary
Forms h bonds within itself - causes it to twist: amino acid attaches to 3" end, anticodon - on the other end (will base-pair with codon sequence of mrna, there is a trna for every amino acid. Initiation: the small subunit binds to, mrna. Initiator trna: modified base of mrna helps ribosome read the rna. Sets the reading frame (3 nucleotides at a time from the start codon: large subunit, binds with the initiator trna in the p site, requires energy (gtp, elongation, grows the polypeptide chain. Codon recognition: next trna enters (carrying correct anticodon, amino acid, base pairs with mrna codon, uses 2 gtp. Peptide bond formation: peptide bond forms between amino acids in p and a site, existing strand of amino acids are added to amino acid in the a site, high energy bond - no extra energy required. Polyribosomes: multiple proteins can be synthesised simultaneously. Rna modification: adds cap and tail, splices out introns.
