BIOL 3510 1st Edition Lecture 6Outline of Last Lecture I. Intro to TranscriptionII. Types of RNAIII. Bacterial TranscriptionIV. Eukaryotic TranscriptionOutline of Current Lecture I. Coding Amino AcidsII. RIbosomesIII. Process of Translationa. Initiationb. TerminationCurrent LectureCoding 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 codonsLarge subunits = catalyzes peptide bond formation Ribosomes have binding sites for mRNA and tRNA.A = aminoacyl-tRNAP = peptidyl-tRNAE = 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 bondStep 3. Large subunit translocatesStep 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 translationStop codons: UAA, UAG, UGA1. Bind ing of release factor to the A-site2. Hydrolysis
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