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the Genetic Code

the Genetic Code. Shown as mRNA 5′ → 3′ 64 codons Redundant One “start” codon: AUG Three “stop” codons: UAG, UAA, UGA (don’t encode amino acids). template strand. mRNA. CUACGAGGAGGUGAAGCGAUGCCCCGUAGCCGAUAGUAGC. 3’. 5’. the Genetic Code.

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the Genetic Code

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  1. the Genetic Code • Shown as mRNA • 5′ → 3′ • 64 codons • Redundant • One “start” codon: AUG • Three “stop” codons: UAG, UAA, UGA (don’t encode amino acids)

  2. template strand mRNA CUACGAGGAGGUGAAGCGAUGCCCCGUAGCCGAUAGUAGC 3’ 5’ the Genetic Code • For each gene, one DNA strand is transcribed • Template strand “read” • mRNA complementary to template CTACGAGGAGGTGAAGCGATGCCCCGTAGCCGATAGTAGC 3’ 5’ DNA GATGCTCCTCCACTTCGCTACGGGGCATCGGCTATCATCG 5’ 3’

  3. non-template strand mRNA CUACGAGGAGGUGAAGCGAUGCCCCGUAGCCGAUAGUAGC 3’ 5’ the Genetic Code • Non-template strand looks like RNA (except T’s) also called the sense strand CTACGAGGAGGTGAAGCGATGCCCCGTAGCCGATAGTAGC 3’ 5’ DNA GATGCTCCTCCACTTCGCTACGGGGCATCGGCTATCATCG 5’ 3’

  4. codons start codon: AUG stop codon: UAG, UGA or UAA the Genetic Code • Ribosome starts at 5’ end of mRNA (in eukaryotes) • Protein synthesis begins at start codon, ends at stop codon mRNA CUACGAGGAGGUGAAGCGAUGCCCCGUAGCCGAUAGUAGC 3’ 5’ protein MetProArgSerArg this stop codon is not “in-frame” so it’s ignored!

  5. Mutation • Change in nucleotide sequence of DNA • Caused by: • DNA polymerase mistake • Chemical change within cell • UV light or other radiation • Mutagenic chemical

  6. Effects of mutations DNA ACGATCCTATGCCCCGCAGCCGATAGTCTCATT TGCTAGGATACGGGGCGTCGGCTATCAGAGTAA 5’ 3’ 3’ 5’ RNA ACGAUCCUAUGCCCCGCAGCCGAUAGUCUCAUU 5’ 3’

  7. MetProArgSerArg Effects of mutations DNA ACGATCCTATGCCCCGCAGCCGATAGTCTCATT TGCTAGGATACGGGGCGTCGGCTATCAGAGTAA 5’ 3’ 3’ 5’ RNA ACGAUCCUAUGCCCCGCAGCCGAUAGUCUCAUU 5’ 3’

  8. MetProArg???Arg Effects of mutations Missense: single amino-acid change DNA ACGATCCTATGCCCCGCCGCCGATAGTCTCATT TGCTAGGATACGGGGCGGCGGCTATCAGAGTAA 5’ 3’ 3’ 5’ RNA ACGAUCCUAUGCCCCGCCGCCGAUAGUCUCAUU 5’ 3’ Could this change have an effect on protein function? Could it affect the whole organism?

  9. MetProArgArgArg Effects of mutations Missense: single amino-acid change DNA ACGATCCTATGCCCCGCCGCCGATAGTCTCATT TGCTAGGATACGGGGCGGCGGCTATCAGAGTAA 5’ 3’ 3’ 5’ RNA ACGAUCCUAUGCCCCGCCGCCGAUAGUCUCAUU 5’ 3’ Could this change have an effect on protein function? Could it affect the whole organism?

  10. Effects of mutations Missense: single amino-acid change Wild-type RPE65: ATGTCTATCCAGGTTGAGCATCCTGCTGGTGGTTACAAGAAACTGTTTGAAACTGTGGAGGAACTGTCCT CGCCGCTCACAGCTCATGTAACAGGCAGGATCCCCCTCTGGCTCACCGGCAGTCTCCTTCGATGTGGGCC AGGACTCTTTGAAGTTGGATCTGAGCCATTTTACCACCTGTTTGATGGGCAAGCCCTCCTGCACAAGTT… MetSerIleGlnValGluHisProAlaGlyGlyTyrLysLysLeuPheGluThrValGluGluLeuSerSerPro LeuThrAlaHisValThrGlyArgIleProLeuTrpLeuThrGlySerLeuLeuArgCysGlyProGlyLeuPhe GluValGlySerGluProPheTyrHisLeuPheAspGlyGlnAlaLeuLeuHisLysPheAspPheLysGlu… Mutant RPE65: ATGTCTATCCAGGTTGAGCATCCTGCTGGTGGTTACAAGAAACTGTTTGAAACTGTGGAGGAACTGTCCT CGCCGCTCACAGCTCATGTAACAGGCAGGATCCCCCTCTGGCTCACCAGCAGTCTCCTTCGATGTGGGCC AGGACTCTTTGAAGTTGGATCTGAGCCATTTTACCACCTGTTTGATGGGCAAGCCCTCCTGCACAAGTT… MetSerIleGlnValGluHisProAlaGlyGlyTyrLysLysLeuPheGluThrValGluGluLeuSerSerPro LeuThrAlaHisValThrGlyArgIleProLeuTrpLeuThrSerSerLeuLeuArgCysGlyProGlyLeuPhe GluValGlySerGluProPheTyrHisLeuPheAspGlyGlnAlaLeuLeuHisLysPheAspPheLysGlu…

  11. Effects of mutations Missense: single amino-acid change Hemoglobin → sickle-cell anemia: ATGGTGCATCTGACTCCTGAGGAG… MetValHisLeuThrProGluGlu GTG Val

  12. AUGCCCCGCAGCCGAUAG MetProArgSerArg AUGCCCCGCAGCUGAUAG Effects of mutations Nonsense: creates stop codon MetProArgSerXXX

  13. AUGCCCCGCAGCCGAUAG MetProArgSerArg Effects of mutations Deletion: creates frameshift, changes all following aa’s AUGCCCGCAGCUGAUAG MetProAlaAlaAsp…

  14. Effects of mutations Insertion: creates frameshift, changes all following aa’s AUGCCCCGCAGCCGAUAG MetProArgSerArg AUGGCCCCGCAGCUGAUAG MetAlaProGlnProIle…

  15. AUGCCCCGCAGCCGAUAG MetProArgSerArg AUGCCCCGCAGUCGAUAG Effects of mutations Silent: DNA changes, but protein doesn’t MetProArgSerArg

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