Operon units of related genes on chromosomes zinc

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Operon – units of related genes on chromosomes Zinc fingers Repressors – regulatory proteins that bind to DNA and block transcription Anticodon – the sequence of three bases on tRNA that combines with the complementary triplet codon on mRNA Antibiotics Peptidyl transferase Lac operon Post-translational modification – a set of reactions that changes the structure of newly synthesized polypeptides Study Guide Roles of mRNA, tRNA, and rRNA in translation mRNA – messenger RNA, a copy of DNA blueprint of the gene to be expressed tRNA – 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 ribosome Ribosomal components Prokaryotic Ribosomes - 70s – 3rRNAs, 55 proteins Eukaryotic Ribosomes – 80s – 4 rRNAs, 82 proteins * protein synthesis – begins from amino end to carboxyl end, mRNA is read from 5 3’ 3 characteristics of ribosome 1. move along mRNA, reading genetic code 2. bring adaptor molecule containing the appropriate amino acid to the template 3. catalyze formation of peptide bond
tRNA structure, especially acceptor stem and anticodon loop, ATP requirement for synthesis of aminoacyl-tRNA structure 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-adenylate Features of the genetic code: and Wobble factor Triplet – three bases equal 1 amino acid Nonoverlapping No punctuation (start, or stop) – AUG (Met, start), Stop (UUA, UGA, UAG) Degenerate – multiple codons signal for same amino acids Universal – 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-Methionine 1. dissociated 30S and 50S ribosomal subunits 2. mRNA to be translated 3. protein intiation factors (IF) 4. the beginning amino acid in activated form fMet-tRNA 5. GTP Process:: 1. mRNA, IF and 30s subunit form a complex AUG must be included in 30s a. 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 building Elongation: components, 3 steps especially peptide bond formation by peptidyl transferase 1. complete 70s ribosome, containing mRNA 2. elgonation factors (EFs) 3. tRNAs 4. GTP Steps for elongation: fMet-tRNA must first bind to Psite - AUG 1. Aminoacyl-tRNA binding a. Corresponding aminoactyl-tRNA for second codon binds to A site (requires EF and GTP) 2.

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