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Operon – units of related genes on chromosomesZinc fingersRepressors – regulatory proteins that bind to DNA and block transcriptionAnticodon – the sequence of three bases on tRNA that combines with the complementary triplet codon on mRNAAntibioticsPeptidyl transferaseLac operonPost-translational modification – a set of reactions that changes the structure of newly synthesized polypeptidesStudy GuideRoles of mRNA, tRNA, and rRNA in translationmRNA – messenger RNA, a copy of DNA blueprint of the gene to be expressedtRNA – Aminoacyl transfer RNA, also called an adaptor molecule. One or more distinct tRNAs for each amino acid. rRNA – ribosomal RNA, catalytic and structural role in protein synthesis; together with proteins make up the RIBOSOME – protein synthesis happens on ribosomeRibosomal componentsProkaryotic Ribosomes - 70s – 3rRNAs, 55 proteinsEukaryotic Ribosomes – 80s – 4 rRNAs, 82 proteins* protein synthesis – begins from amino end to carboxyl end, mRNA is read from 53’3 characteristics of ribosome1. move along mRNA, reading genetic code2. bring adaptor molecule containing the appropriate amino acid to the template3. catalyze formation of peptide bond
tRNA structure, especially acceptor stem and anticodon loop, ATP requirement for synthesis of aminoacyl-tRNAstructure of tRNA – 3 leave clover. Middle one has anticodon which has a code (UUA etc.) which then codes for amino acid to bind to 2 or 3’ end of tRNA (stem of clover)ATP requirement – one ATP reacts with 1 amino acid to form Aminoacyl-adenylateFeatures of the genetic code: and Wobble factorTriplet – three bases equal 1 amino acidNonoverlappingNo punctuation (start, or stop) – AUG (Met, start), Stop (UUA, UGA, UAG) Degenerate – multiple codons signal for same amino acidsUniversal – except with a few exceptions (mitochondria)Wobble Factor – first two bases are stronger bonds, last base has weaker bond (wobble factor) three factors – 1. adds flexibility to genetic code 2. weaker interaction causes faster dissociation of tRNA form mRNA – speeding protein synthesis, 3. minimizes effects of mutations. Initiation: components, Shine-Dalgarno sequence, N-formyl-Methionine1.dissociated 30S and 50S ribosomal subunits 2.mRNA to be translated3.protein intiation factors (IF)4.the beginning amino acid in activated form fMet-tRNA5.GTPProcess::1.mRNA, IF and 30s subunit form a complex AUG must be included in 30sa.Shine Dalgarno sequence helps direct to first AUG codon (AGGAGGU)2.fMet-tRNA and GTP bind (this is the first amino acid)3.50s subunit attaches forming 70s subunit, GTP hydrolyzed and IF is removed so ribosome attaches and can begin protein buildingElongation: components, 3 steps especially peptide bond formation by peptidyl transferase1.complete 70s ribosome, containing mRNA2.elgonation factors (EFs)3.tRNAs4.GTPSteps for elongation: fMet-tRNA must first bind to Psite - AUG1.Aminoacyl-tRNA bindinga.Corresponding aminoactyl-tRNA for second codon binds to A site (requires EF and GTP)2.