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Mutations

Mutations. Mutation. Permanent changes or errors in a DNA sequence Copied during DNA replication Therefore heritable OR may occur during transcription to mRNA sequence. Germ Cell Mutation. Occur in reproductive cells of an organism Will be passed on to offspring. Somatic Cell Mutation.

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Mutations

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  1. Mutations

  2. Mutation • Permanent changes or errors in a DNA sequence • Copied during DNA replication • Therefore heritable • OR may occur during transcription to mRNA sequence

  3. Germ Cell Mutation • Occur in reproductive cells of an organism • Will be passed on to offspring

  4. Somatic Cell Mutation • Occurs in body cells • Side effects may be: • Negative • Positive • There may be none

  5. Sickle Cell Anemia Normal hemoglobin DNA Mutant hemoglobin DNA mRNA mRNA Sickle-cell hemoglobin Normal hemoglobin Glu Val

  6. Causes • Exposure to mutagenic agents • UV (ultraviolet) radiation • Cosmic rays • Chemicals – e.g. pesticides • X rays

  7. Types of Mutations Point Mutation a.k.a – Gene Mutation Only one or a few nucleotides are affected Chromosomal Affects multiple genes May affect genes on separate chromosomes

  8. Substitution • Replacement of one base by another • AAG CCC GGC AAA • AAG ACC GGC AAA mRNA Protein Met Lys Phe Gly Ala Base substitution Met Lys Phe Ser Ala

  9. Possible Results Missense mutation Only one amino acid is changed DNA RNA Amino Acid CCC = GGG = Gly ACC = UGG = Trp

  10. Possible Results Nonsense Mutation Amino acid in middle of protein is changed to a stop codon Protein not complete & inactive DNA Amino Acid GTA AGT CGG = His – Ser - Ala GTA ACT CGG = His – STOP - Ala

  11. Possible Results Silent Mutation Amino acid is not changed DNA RNA Amino Acid CTA = GAU = Asp CTG = GAC = Asp

  12. Deletion Elimination of one or more base pairs AAG CCC GGC AAA AA CCC GGC AAA ← shift over AAC CCG GCA AA

  13. Addition/Insertion Placement of one or more base pairs AAG CCC GGC AAA AAG ACC CGG CAA A

  14. Reading Frame • The sun was hot but the old man did not get his hat. • Letters = base pairs (3 letters = codon) • Words = amino acid • Sentence = protein • T hes unw ash otb utt heo ldm and idn otg eth ish at. • Th esu nwa sho tbu tth eol dma ndi dno tge thi sha t.

  15. Possible Results Frameshift mutation • Moves ‘reading frame’ • Codon = 3 bases • Changes many amino acids Note: • May also result in a nonsense mutation

  16. Deletion Mutation • Result: • Frameshift mRNA Protein Met Lys Phe Gly Ala Nucleotide deletion Met Lys Leu Ala His

  17. mRNA = GCU ACU CAA UUC • Translate the mRNA above. • Translate each mutated mRNA below. • GCU ACU CGA UUC • GCU ACG CAA UUC • GCU ACU UCAAUUC • What was the result of each mutation? • Which would be most harmful?

  18. Task • Page 263 • Answer #2 to 7 • Omit #6(e) • For #5: list a maximum of 10

  19. #2 – Additions more harmful than substitutions? • Substitution • May be silent • May change only one amino acid • Result: minor protein change • Addition • Changes reading frame • Result: completely new protein • Exception • If substitution resulted in a nonsense mutation

  20. #3 – Nonsense vs. Missense • Nonsense: • Translation ends before protein is complete • Protein = inactive • Missense: • One amino acid changed • Protein = may/may not function properly • Which is more harmful?

  21. #4 – Causes UV radiation Cosmic rays X rays Chemicals – e.g. pesticides

  22. #5 – Create Stop Codon • Stop codons: • UGA, UAA, UAG • Change one base to become stop codon: • UAU, UAC, UGU, UGC, UGG, UUA, UCA, UUG, UCG, CGA, AGA, GGA, CAA, CAG, AAA, AAG, GAA, GAG

  23. #6(a) – Harmful? • Original strand: • AUG–UUU–UUG–CCU–UAU–CAU–CGU • met–phe–leu–pro–tyr–his–arg • Change to: UAC • New protein: • met–phe–leu–pro–tyr–his–arg • Silent = not harmful • Protein unchanged

  24. #6(b) – Harmful? • Original strand: • AUG–UUU–UUG–CCU–UAU–CAU–CGU • met–phe–leu–pro–tyr–his–arg • Change to: UAA • New protein: • met–phe–leu–pro–STOP • Nonsense = harmful • Nonfunctioning protein

  25. #6(c) – Harmful? insert a C and shift over • Original strand: • AUG–UUU–UUG–CCU–UAU–CAU–CGU • met–phe–leu–pro–tyr–his–arg • New protein: • met–phe–leu–ala–leu–leu–leu • Frameshift mutation = harmful • Different amino acids (new protein)

  26. #6(d) – Harmful? Delete and shift over • Original strand: • AUG–UUU–UUG–CCU–UAU–CAU–CGU • met–phe–leu–pro–tyr–his–arg • New protein: • met–phe–leu–pro–ile–ile • Frameshift mutation = harmful • Different amino acids (new protein)

  27. #7(a) – Single Substitution • Arginine → Leucine • With the following substitutions: • CGU → CUU • CGC → CUC • CGA → CUA • CGG → CUG

  28. #7(b) – Single Substitution • Cysteine → Glutamic acid • Cannot be done with one base pair substitution

  29. #7(c) – Single Substitution • Serine → Threonine • With the following substitutions: • AGU → ACU • AGC → ACC • UCU → ACU • UCC → ACC • UCA → ACA • UCG → ACG

  30. #7(d) – Single Substitution • Isoleucine → Serine • With the following substitutions: • AUU → AGU • AUC → AGC

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