BCH4024 - Long Lecture 51

BCH4024 - Long Lecture 51 - 1 tRNA (provides amino acids)...

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Unformatted text preview: 1 tRNA (provides amino acids) Ribosome (complex of rRNA and proteins where translation occurs) Flow of genetic information --- the Central Dogma DNA RNA Protein Replication Transcription Translation mRNA (primary sequence) Lecture 54: Translation (protein synthesis) Todays lecture: Chapter 27a Download from http://lss.at.ufl.edu tRNA is the adaptor molecule for RNA amino acid Each tRNA contains a nucleotide triplet or anti codon complimentary to the mRNA for a particular amino acid Aminoacyl-tRNA synthetase attaches a particular tRNA to its corresponding amino acid tRNA has extensive self- complimentarity and is much more stable than mRNA 2 Genetic Code tRNA is an adapter molecule between nucleotide language and amino acid language a) Coding ratio: 3 nucleotides / amino acid b) Codon assignments: 4 bases, taken 3 at a time 4 3 = 64 possible combinations 61 codons encode (usually) for 20 amino acids 3 codons are (usually) stop signals c) Redundant More than one codon for all amino acids except Met and Trp d) Non-ambiguous A given codon specifies one and only one amino acid e) Non-overlapping The ribosome must maintain a reading frame of three bases at a time to properly translate mRNA. On some rare occasions, depending on structural properties of the mRNA, four bases may be read CATGAG vs. CATGAG This would cause statistically favored amino acid combinations Deciphering the genetic code Which codons encode which amino acids? How is the code read? (Francis Crick & Sidney Brenner 1961) point mutations (single nucleotide) change only one amino acid one or two nucleotide insertions or deletions produce nonsense proteins three nucleotide deletions/insertions remove/add one amino acid 3 Marshall Nirenberg et al. (1961) devised a cell-free translation system (tRNAs, amino acids, aminoacyl synthetases and ribosomes) Adding polynucleotides (AAAAAA. or CCCCCC..) yielded polyproline and polylysine so AAA translates to proline and CCC encodes lysine H.G. Khorana synthesized polyRNAs with different repeating structures H....
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BCH4024 - Long Lecture 51 - 1 tRNA (provides amino acids)...

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