07 gene mutations

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07 gene mutations

  1. 1. GENE MUTATIONSaka point mutations
  2. 2. Gene mutations which affect only one gene DNA sequence Transcription ↓ mRNA sequence Translation ↓ Polypeptide© 2010 Paul Billiet ODWS
  3. 3. Normal gene DNA (antisense strand) GGTCTCCTCACGCCA ↓ mRNA CCAGAGGAGUGCGGU Codons ↓ Polypeptide Pro-Glu-Glu-Cys-Gly Amino acids The antisense strand is the DNA strand which acts as the template for mRNA transcription© 2010 Paul Billiet ODWS
  4. 4. Mutations: Substitutions Normal gene Substitution mutation GGTCTCCTCACGCCA GGTCACCTCACGCCA ↓ ↓ CCAGAGGAGUGCGGU CCAGUGGAGUGCGGU Codons ↓ ↓ Pro-Glu-Glu-Cys-Gly Pro-Arg-Glu-Cys-Gly Amino acids Substitutions will only affect a single codon Their effects may not be serious unless they affect an amino acid that is essential for the structure and function of the finished protein molecule (e.g. sickle cell anaemia)© 2010 Paul Billiet ODWS
  5. 5. The genetic code is degenerate A mutation to have no effect on the phenotype Changes in the third base of a codon often have no effect.© 2010 Paul Billiet ODWS
  6. 6. No change Normal gene Substitution mutation GGTCTCCTCACGCCA GGTCTTCTCACGCCA ↓ ↓ CCAGAGGAGUGCGGU CCAGAAGAGUGCGGU Codons ↓ ↓ Pro-Glu-Glu-Cys-Gly Pro-Glu-Glu-Cys-Gly Amino acids© 2010 Paul Billiet ODWS
  7. 7. Disaster Normal gene Substitution mutation GGTCTCCTCACGCCA GGTCTCCTCACTCCA ↓ ↓ CCAGAGGAGUGCGGU CCAGAAGAGUGAGGU Codons ↓ ↓ Pro-Glu-Glu-Cys-Gly Pro-Glu-Glu-STOP Amino acids© 2010 Paul Billiet ODWS
  8. 8. Mutations: Inversion Inversion mutations, also, only affect a small part of the gene Normal gene Inversion mutation GGTCTCCTCACGCCA GGTCCTCTCACGCCA ↓ ↓ CCAGAGGAGUGCGGU CCAGGAGAGUGCGGU Codons ↓ ↓ Pro-Glu-Glu-Cys-Gly Pro-Gly-Glu-Cys-Gly Amino acids© 2010 Paul Billiet ODWS
  9. 9. Mutations: Additions A frame shift mutation Normal gene Addition mutation GGTCTCCTCACGCCA GGTGCTCCTCACGCCA ↓ ↓ CCAGAGGAGUGCGGU CCACGAGGAGUGCGGU Codons ↓ ↓ Pro-Glu-Glu-Cys-Gly Pro-Arg-Gly-Val-Arg Amino acids© 2010 Paul Billiet ODWS
  10. 10. Mutations: Deletions A frame shift mutation Normal gene Deletion mutation GGTCTCCTCACGCCA GGTC/CCTCACGCCA ↓ ↓ CCAGAGGAGUGCGGU CCAGGGAGUGCGGU Codons ↓ ↓ Pro-Glu-Glu-Cys-Gly Pro-Gly-Ser-Ala-Val Amino acids© 2010 Paul Billiet ODWS
  11. 11. Mutations of haemoglobin  Haemoglobin is a tetramer = 2 α and 2 β-chains  The genes for these polypeptides are found on different chromosomes  The β-chain gene is found on chromosome 11  The α-chain gene is found on chromosome 16  The nucleotide sequences have been worked out  Several inherited diseases occur on the β-chain, which contains 146 amino acids.© 2010 Paul Billiet ODWS
  12. 12. β haemoglobin sense strand cDNA sequence  cDNA (complementary DNA) is obtained by back-transcribing the mRNA used to translate the polypeptide  So cDNA has no introns  This is done using reverse transcriptase enzyme.© 2010 Paul Billiet ODWS
  13. 13. Methionine initiator ATG GTG CAT CTG ACT CCT GAG GAG AAG TCT GCC GTT ACT GCC CTG TGG GGC AAG GTG AAC GTG GAT GAA GTT GGT GGT GAG GCC CTG GGC AGG CTG CTG GTG GTC TAC CCT TGG ACC CAG AGG TTC TTT GAG TCC TTT GGG GAT CTG TCC ACT CCT GAT GCT GTT ATG GGC AAC CCT AAG GTG AAG GCT CAT GGC AAG AAA GTG CTC GGT GCC TTT AGT GAT GGC CTG GCT CAC CTG GAC AAC CTC AAG GGC ACC TTT GCC ACA CTG AGT GAG CTG CAC TGT GAC AAG CTG CAC GTG GAT CCT GAG AAC TTC AGG CTC CTG GGC AAC GTG CTG GTC TGT GTG CTG GCC CAT CAC TTT GGC AAA GAA TTC ACC CCA CCA GTG CAG GCT GCC TAT CAG AAA GTG GTG GCT GGT GTG GCT AAT GCC CTG GCC CAC AAG TAT CAC TAA Nonsense terminator© 2010 Paul Billiet ODWS
  14. 14. Mutation Codon Change to DNA Change in sense strand Amino Acid S (sickle cell 6 GAG to GTG Glu to Val anaemia) C (cooley’s 6 GAG to AAG Glu to Lys syndrome) GSan Jose 7 GAG to GGG Glu to Gly E 26 GAG to AAG Glu to Lys MSaskatoon 63 CAT to TAT His to Tyr MMilwauki 67 GTG to GAG Val to Glu OArabia 121 GAA to GTA Glu to Val© 2010 Paul Billiet ODWS
  15. 15. Sickle Cell Anaemia Sickle cell anemia Image Credit: http://explore.ecb.org/Blood smear (normal)Image Credit: http://lifesci.rutgers.edu/~babiarz/

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