Chapter 15- part 1

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  • Figure 15.3 Method used to determine the relation between genes and enzymes in Neurospora. This biochemical pathway leads to the synthesis of arginine in Neurospora. Steps in the pathway are catalyzed by enzymes affected by mutations.
  • B-A-C
  • Figure 15.8 (part 1) Nirenberg and Matthaei developed a method for identifying the amino acid specified by a homopolymer.
  • Figure 15.8 (part 2) Nirenberg and Matthaei developed a method for identifying the amino acid specified by a homopolymer.
  • Figure 15.9 Nirenberg and Leder used ribosome-bound tRNAs to provide additional information about the genetic code.
  • Figure 15.9 (part 1) Nirenberg and Leder used ribosome-bound tRNAs to provide additional information about the genetic code.
  • Figure 15.9 (part 2) Nirenberg and Leder used ribosome-bound tRNAs to provide additional information about the genetic code.
  • Figure 15.9 (part 3) Nirenberg and Leder used ribosome-bound tRNAs to provide additional information about the genetic code.
  • Figure 15.10 The genetic code consists of 64 codons. The amino acids specified by each codon are given in their three-letter abbreviation. The codons are written 5 ′  3 ′ , as they appear in the mRNA. AUG is an initiation codon; UAA, UAG, and UGA are termination (stop) codons.
  • Figure 15.11 Wobble may exist in the pairing of a codon and anticodon.
  • Letter D
  • Chapter 15- part 1

    1. 1. LECTURE CONNECTIONS 15 | The Genetic Code and Translation © 2009 W. H. Freeman and Company
    2. 2. 15.1 Many Genes Encode Proteins <ul><li>The One Gene One Enzyme Hypothesis: </li></ul><ul><ul><li>Genes function by encoding enzymes, and each gene encodes a separate enzyme. </li></ul></ul><ul><ul><li>More specific: one gene one polypeptide hypothesis. </li></ul></ul><ul><ul><li>In 1940s, Beadle and Tatum performed experiments in Neurospora (fungus). </li></ul></ul>
    3. 6. Precursor Ornithine Citrulline Arginine Group I mutations Group II mutations Group III mutations
    4. 7. Concept Check 1 Auxotrophic mutation 103 grows on minimal medium supplemented with A, B, or C. Mutation 106 grows on medium supplemented with A and C, but not B; and mutation 102 grows only on medium supplemented with C. What is the order of A, B, C in a biochemical pathway?
    5. 8. Proteins
    6. 9. 15.2 The Genetic Code Determines How the Nucleotide Sequence Specifies the Amino Acid Sequence of a Protein <ul><li>Codon: the set of bases that encode an aa. (The genetic code is a triplet code). </li></ul><ul><li>Which group of three nucleotides specify which amino acids? </li></ul><ul><li>In 1964, Nirenberg and Matthaei created a synthetic RNAs by using an enzyme called polynucleotide phosphorylase. </li></ul>
    7. 12. <ul><li>Nirenberg and Leder used ribosome-bound tRNAs to provide additional information about the genetic code. Short sequences of mRNA would bind to a ribosome. </li></ul><ul><li>The codon on the short mRNA would then base pair with the matching anticodon on a tRNA that carried the aa specified by the codon. </li></ul>
    8. 16. <ul><li>Each nucleotide can have one of four possible bases (A, G, C and U) at each nucleotide position, thus permitting 4 3 = 64 possible codons. </li></ul><ul><li>Sense codons: encoding amino acid (61 codons) </li></ul><ul><li>Initiation codon: AUG </li></ul><ul><li>Termination codon: UAA, UAG, UGA </li></ul><ul><li>61 sense codons and 20 aa- the code contains more information than is needed to specify the aa: degenerate code </li></ul>The Degeneracy of the Code
    9. 18. <ul><li>Degenerate code: Amino acid may be specified by more than one codon. </li></ul><ul><li>Synonymous codons: codons that specify the same amino acid </li></ul><ul><li>Isoaccepting tRNAs: different tRNAs that accept the same amino acid but have different anticodons </li></ul><ul><li>Wobble hypothesis There are still more codons than anticodons, because different codons can sometimes pair with the same anticodon through flexibility in base pairing at the third position of the codon. </li></ul>The Degeneracy of the Code
    10. 19. The mRNA and tRNA pair in an antiparallel fashion. Pairing at the first and second codon positions is in accord with the Watson and Crick pairing rules (A with U, G with C); however, pairing rules are relaxed at the third position of the codon, and G on the anticodon can pair with either U or C on the codon in this example.
    11. 20. Concept Check 2 <ul><ul><li>codon, anticodon </li></ul></ul><ul><ul><li>group of three nucleotides in DNA, codon in mRNA </li></ul></ul><ul><ul><li>tRNA, amino acid </li></ul></ul><ul><ul><li>anticodon, codon </li></ul></ul>Through wobble, a single can pair with more than one . <ul><li>Wobble allows some tRNAs to pair with more than one codon on an mRNA; thus from 30 to 50 tRNAs can pair with 61 sense codons. </li></ul>
    12. 21. 15.1 Many Genes Encode Proteins <ul><li>The One Gene One Enzyme Hypothesis: </li></ul><ul><ul><li>Genes function by encoding enzymes, and each gene encodes a separate enzyme. </li></ul></ul><ul><ul><li>More specific: one gene one polypeptide hypothesis </li></ul></ul>
    13. 22. <ul><li>Reading frame: three ways in which the sequence can be read in groups of three. Each different way of reading encodes a different amino acid sequence. Initiation code AUG Termination code UAA, UAG, UGA </li></ul><ul><li>Nonoverlapping: A single nucleotide may not be included in more than one codon. </li></ul><ul><li>The universality of the code: near universal, with some exceptions </li></ul>The Reading Frame and Initiation Codons

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