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 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?
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
15.2 The Genetic Code Determines How the Nucleotide Sequence Specifies the Amino Acid Sequence of a Protein
Breaking the Genetic Code
Codon: a triplet RNA code Breaking the Genetic 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 The Degeneracy of the Code
Sense codons: encoding amino acid Initiation codon: AUG Termination codon: UAA, UAG, UGA The Degeneracy of the Code
Concept Check 2 Through wobble, a single can pair with more than one. a.codon, anticodon b.group of three nucleotides in DNA, codon in mRNA c.tRNA, amino acid d.anticodon, codon
Concept Check 2 Through wobble, a single can pair with more than one. a.codon, anticodon b.group of three nucleotides in DNA, codon in mRNA c.tRNA, amino acid d.anticodon, codon
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
15.2 The Genetic Code Determines How the Nucleotide Sequence Specifies the Amino Acid Sequence of a Protein
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 The Reading Frame and Initiation Codons
15.3 Amino Acid Are Assembled into a Protein Through the Mechanism of Translation
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. The Binding of Amino Acids to Transfer RNAs
Initiation factors IF-3, initiator tRNA with N- formylmethionine attached to form fmet-tRNA Energy molecule: GTP 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. The Initiation of Translation
Exit site E Peptidyl site P Aminoacyl site A Elongation factors: Tu, Ts, and G Elongation
Concept Check 3 In elongation, the creation of peptide bonds between amino acids is catalyzed by. a.rRNA b.protein in the small subunit c.protein in the large subunit d.tRNA
Concept Check 3 In elongation, the creation of peptide bonds between amino acids is catalyzed by. a.rRNA b.protein in the small subunit c.protein in the large subunit d.tRNA
Termination codons: UAA, UAG, and UGA Release factors Termination
The three-dimensional structure of the ribosome Polyribosomes: –An mRNA with several ribosomes attached 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 15.4 Additional Properties of RNA and Ribosomes Affect Protein Synthesis