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15.1 Many Genes Encode Proteins

15.1 Many Genes Encode Proteins. The One Gene One Enzyme Hypothesis: Genes function by encoding enzymes, and each gene encodes a separate enzyme. More specific: one gene one polypeptide hypothesis. Concept Check 1.

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15.1 Many Genes Encode Proteins

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  1. 15.1 Many Genes Encode Proteins • The One Gene One Enzyme Hypothesis: • Genes function by encoding enzymes, and each gene encodes a separate enzyme. • More specific: one gene one polypeptide hypothesis

  2. 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?

  3. 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? B  A  C

  4. 15.2 The Genetic Code Determines How the Nucleotide Sequence Specifies the Amino Acid Sequence of a Protein

  5. Breaking the Genetic Code

  6. Breaking the Genetic Code • Codon: a triplet RNA code

  7. The Degeneracy of the Code • Degenerate code: Amino acid may be specified by more than one codon. • Synonymous codons: codons that specify the same amino acid • Isoaccepting tRNAs: different tRNAs that accept the same amino acid but have different anticodons • Wobble hypothesis

  8. The Degeneracy of the Code • Sense codons: encoding amino acid • Initiation codon: AUG • Termination codon: UAA, UAG, UGA

  9. Concept Check 2 Through wobble, a single can pair with more than one . • codon, anticodon • group of three nucleotides in DNA, codon in mRNA • tRNA, amino acid • anticodon, codon

  10. Concept Check 2 Through wobble, a single can pair with more than one . • codon, anticodon • group of three nucleotides in DNA, codon in mRNA • tRNA, amino acid • anticodon, codon

  11. 15.1 Many Genes Encode Proteins • The One Gene One Enzyme Hypothesis: • Genes function by encoding enzymes, and each gene encodes a separate enzyme. • More specific: one gene one polypeptide hypothesis

  12. 15.2 The Genetic Code Determines How the Nucleotide Sequence Specifies the Amino Acid Sequence of a Protein

  13. The Reading Frame and Initiation Codons • 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. • Nonoverlapping: A single nucleotide may not be included in more than one codon. • The universality of the code: near universal, with some exceptions

  14. 15.3 Amino Acid Are Assembled into a Protein Through the Mechanism of Translation

  15. The Binding of Amino Acids to Transfer RNAs • Aminoacyl-tRNA syntheses and tRNA charging • The specificity between an amino acid and its tRNA is determined by each individual aminoacyl-tRNA synthesis. There are exactly 20 different aminoacylt-tRNA syntheses in a cell.

  16. The Initiation of Translation • Initiation factors IF-3, initiator tRNA with N-formylmethionine attached to form fmet-tRNA • Energy molecule: GTP

  17. The Initiation of Translation • The Shine–Dalgarno consensus sequence in bacterial cells is recognized by the small unit of ribosome. • The Kozak sequence in eukaryotic cells facilitates the identification of the start codon.

  18. Elongation • Exit site E • Peptidyl site P • Aminoacyl site A • Elongation factors: Tu, Ts, and G

  19. Concept Check 3 In elongation, the creation of peptide bonds between amino acids is catalyzed by . • rRNA • protein in the small subunit • protein in the large subunit • tRNA

  20. Concept Check 3 In elongation, the creation of peptide bonds between amino acids is catalyzed by . • rRNA • protein in the small subunit • protein in the large subunit • tRNA

  21. Termination • Termination codons: UAA, UAG, and UGA • Release factors

  22. 15.4 Additional Properties of RNA and Ribosomes Affect Protein Synthesis • The three-dimensional structure of the ribosome • Polyribosomes: • An mRNA with several ribosomes attached

  23. 15.4 Additional Properties of RNA and Ribosomes Affect Protein Synthesis • Messenger RNA surveillance: • Detect and deal with errors in mRNA • Nonsense – mediated mRNA decay: eliminating mRNA containing premature termination codons • The posttranslational modifications of proteins

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