BIOL-L211 Lecture 29 Outline of Last Lecture I. RecapII. Gene Silencing by miRNAs and siRNAsIII. ArticleOutline of Current Lecture I. Genetic CodeII. Cracking the Genetic CodeIII. Degeneracy of the Genetic CodeCurrent LectureIntroduction to Genetic CodeI. Genetic CodeA. Codon: set of three bases that codes for a specific amino acid1. One amino acid can be coded for by multiple codons2. AUG = start codon (first to be read) encodes methionine (Met)3. UGA, UAA, and UAG = stop codons (do not code proteins)B. Amino Acids: components of proteins (20 naturally occurring)1. All have an amino group, a carboxyl group, and a proton2. Additionally, each amino acid has a unique side chain (R group)a. Side chain determines nature of amino acidC. Open Reading Frames1. Codons are arranged sequentially, and do not overlap2. Start codons determine reading framesThese 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.3. Stop codons determine where reading frames end4. Open Reading Frames (ORF):a. One reading frameb. Codes for one proteinII. Cracking the Genetic CodeA. Original Experiment1. Transcripts made with only U's, A's, and C'sa. All U's: Phenylalanine2. Transcripts made with two alternating nucleotidesa. CAC: Histidineb. ACA: Threonine3. Transcripts made with all possible codon combinationsa. Determined what all codons coded forB. Transfer RNA (tRNAs)1. Non-coding RNA that serve as adaptors between codons and amino acids2. Pol III: transcribes tRNA3. Cloverleaf secondary structure with an acceptor arm and anti-codon regiona. Acceptor Arm: Connects to a specific amino acidb. Anti-codon: Has 3 bases which form base pairs with the codons in mRNA, binding with an antiparallel orientation*Note: Codon read 5'-3'III. Degeneracy of the Genetic CodeA. Genetic code is degenerate because there are 64 possible 3 base pair combinations but only 20 amino acids that are producedB. The Wobble Effect: way by which one tRNA (with its amino acid) can interact with multiple codonsC. The 5' nucleotide of the anticodon is capable of base pairing with more than one type of base at the 3' nucleotide of the codon1. Anticodon G can pair with U or C2. Anticodon C can pair with G3. Anticodon A can pair with U4. Anticodon U can pair with A or G5. Anticodon I (inosine- unique to tRNAs) can pair with A, U, or CD. Certain amino acids can attach to multiple tRNAs (each which recognizes a different possible codon for that specific amino acid)E. Silent Mutations1. Change a single base pair in one codon such that it still codes for the same amino acidF. Missense Mutations1. Change a single base pair in one codon such that it changes the amino acid for which it codesG. Nonsense Mutations1. Change a single base pair to insert an early stop codonH. Frameshift Mutations1. Insert or delete base pairs in amounts not divisible by three such that the amino acid sequence is completely
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