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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. - PowerPoint PPT Presentation
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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, anticodonb. group of three nucleotides in DNA, codon in
mRNAc. tRNA, amino acidd. anticodon, codon
Concept Check 2
Through wobble, a single can pair with more than one .
a. codon, anticodonb. group of three nucleotides in DNA, codon in
mRNAc. tRNA, amino acidd. 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. rRNAb. protein in the small subunitc. protein in the large subunitd. tRNA
Concept Check 3
In elongation, the creation of peptide bonds between amino acids is catalyzed by .
a. rRNAb. protein in the small subunitc. protein in the large subunitd. 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