BIOL 3510 1st Edition Lecture 6 Outline of Last Lecture I Intro to Transcription II Types of RNA III Bacterial Transcription IV Eukaryotic Transcription Outline of Current Lecture I Coding Amino Acids II RIbosomes III Process of Translation a Initiation b Termination Current Lecture Coding Amino Acids How can human cells make 75k 100k different proteins given that there are about 20k genes By alternative splicing How is RNA read Groups of 3 nucleotides codons encode individual amino acids The genetic code is redundant several different codons can specify a single amino acid Three possible reading frames only one frame can make a specific protein The rules by which the nucleotide sequences of a gene through an intermediary mRNA molecule is translated into the amino acid sequence of a protein Transfer RNAs tRNAs link codons to amino acids There must be two binding sites one for the amino acid Some amino acids are attached to multiple tRNAs Some transfer RNAs can bind multiple codons wobble in the third base pair The 1st and 2nd should be correct but the 3rd has a little flexibility for error The number of tRNAs encoded by a genome varies from organism to organism These notes represent a detailed interpretation of the professor s lecture GradeBuddy is best used as a supplement to your own notes not as a substitute In tRNA charging aminoacyl tRNA synthetases connect amino acids to the correct tRNA There are 20 different synthetases tRNA linkage is proofed in two steps Does the amino acid fit in the synthesis site Is the amino acid excluded from the editing site Ribosomes are made of proteins and rRNAs Small subunits matches tRNA to codons Large subunits catalyzes peptide bond formation Ribosomes have binding sites for mRNA and tRNA A aminoacyl tRNA P peptidyl tRNA E exit rRNAs Catalyze the formation of the peptide bond Ex Of a ribozyme Form the mRNA and tRNA binding sites General Process of Translation see Fig 7 34 in Essential Cell Biology 4th ed Step 1 Charging tRNA using ATP on the A site Step 2 Making the peptide bond Step 3 Large subunit translocates Step 4 Small subunit translocates There are two sites but only 2 tRNAs are there Peptide bonds form between an aminoacy tRNA and a peptidyl tRNA positioned in the A and P sites of the ribosome In all cells a special initiator tRNA molecule recognizing the start codon AUG and carrying the amino acid thymine provides the amino acid that begins a protein chain Initiation of Translation eiF eukaryotic initiation factors Formation of complex GTP Termination of translation Stop codons UAA UAG UGA 1 Bind ing of release factor to the A site 2 Hydrolysis occurs
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