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Mutations

Mutations. Sickle Cell Anemia. Mutations. Can be a change in the DNA base sequence or a change in a chromosome Mutant- someone who has a mutation. Consequences of Mutations. Mutations can be Helpful Ex: Give immunity to HIV Ex: Give immunity to infectious diseases Harmless Harmful

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Mutations

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  1. Mutations

  2. Sickle Cell Anemia

  3. Mutations • Can be a change in the DNA base sequence or a change in a chromosome • Mutant- someone who has a mutation

  4. Consequences of Mutations • Mutations can be • Helpful • Ex: Give immunity to HIV • Ex: Give immunity to infectious diseases • Harmless • Harmful • Ex: Disease causing mutations (some have to be in homozygous form)

  5. What do Mutations do? • Can stop or slow the production of a protein • Ex: • Cause a protein to overproduce • Ex: • Impair a protein’s function • Ex:

  6. When can Mutations happen? • Germline mutation- happens before meiosis; affects all cells in the new organism • Somatic mutation- happens before mitosis; after only immediate daughter cells and their descendents • More severe the earlier it occurs • Creates a mosaic • Can lead to some forms of cancer

  7. Spontaneous Mutations • Change occurs with no outside influence • Often occurs because of a mismatch in base pairs during replication • Results in de novo mutations

  8. Mutation Rates • Different in different genes • Depends on • Gene size • Gene location • Gene sequence

  9. Mutation Hot Spots • Sequence Regions • That are repetitive • Symmetrical or repeated sequences on the same strand • Palindromes- sequence that reads the same forward and backward Sections confuse replication enzymes

  10. Mutagen • Substance causing a mutation • Chemicals • Radiation • Exposure can be accidental or purposeful • It can also come from the natural environment

  11. Huntington’s Disease

  12. Types of Mutations • Point mutations- change of a single base • Transition- exchange of one pyrimidine for another or one purine for another • Transversion- exhange of a pyrimidine for a purine or vice versa • Missense mutation- changes one amino acid in polypeptide chain • Nonsense mutation- creates a stop codon in the middle of the polypeptide chain • Splice site mutations- alters the splicing of the pre-mRNA

  13. Types of Mutation (cont) • Frameshift mutations- move the reading frame; can be point mutations; all amino acids after mutation can be affected • Insertion- addition of bases • Tandem duplication- repetition of a sequence placed very close to the original • Deletion- removal of bases

  14. Expanding Repeats • Repeated section of DNA is replicated incorrectly causing extra repeats • Repeats are added to during every generation (higher severity; earlier onset) • Repeats often create symptoms when they reach higher than 40

  15. Other Causes of Mutations • Pseudogenes • Replicate of gene made at earlier time • Currently not used (collected enough mutations) • May still be close enough to cross over with real gene causing mutations in real gene • Transposons (jumping genes) • Jump into working gene causing mutation

  16. Xeroderma Pigmentosum

  17. Minimizing the Effects of Mutation • Position • Change in third position often does nothing • Change in second position often either does nothing or changes one amino acid for a similar one • Conditional mutation • Mutation only affects the phenotype under certain conditions • Stem cell DNA • Stem cell may retain old template DNA strands and send new strands into progenitor cell

  18. DNA Repair: Photoreactivation • DNA is damaged by UVB wavelengths • Forms thymine dimers • extra covalent bond between thymines next to each other on the same strand • forms kinks in DNA; disrupts replication and transcription • Enzymes called photolyases absorb energy from light and break these bonds • Humans do not use this

  19. DNA Repair: Excision Repair • Enzymes snip out section with pyrimidinedimers • DNAP fills in gap with correct nucleotides • Humans have two types • Nucleotide excision repair • Used for many types of damage • Repairosome- group of enzymes that cut out and replace up to 30 nucleotides • Base excision repair • Used for oxidative damage • Replaces up to 5 nucleotides at a time

  20. Nucleotide Excision Repair

  21. Base Excision Repair

  22. DNA Repair: Mismatch Repair • Repairs errors that occur because of replication • Enzymes look for loops in DNA (sign of mismatching) and cut out and repair bases

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