09 mutations-2010 stacy

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09 mutations-2010 stacy

  1. 2. Mutations <ul><li>mutations – errors in the DNA </li></ul><ul><ul><li>can have a bad resultant effect </li></ul></ul><ul><ul><li>can have no effect </li></ul></ul><ul><ul><li>can have a positive resultant effect </li></ul></ul><ul><li>Mutations are usually not an issue because </li></ul><ul><li>we have two copies of each gene. </li></ul><ul><li>What does this mean? </li></ul>
  2. 3. Mutations <ul><li>Changes in DNA result in: </li></ul><ul><ul><li>silent mutations </li></ul></ul><ul><ul><li>missense mutations </li></ul></ul><ul><ul><li>nonsense mutations </li></ul></ul>
  3. 4. Silent Mutations <ul><li>silent mutation – has no effect on the function of the cell; sequence of amino acids is not affected </li></ul><ul><li>often found in the non-coding (regulatory) regions </li></ul><ul><li>third NT of codons can be changed yet still code for the same amino acid (wobble hypothesis) </li></ul>
  4. 5. Missense Mutation <ul><li>missense mutation – nucleotide sequence is changed such that a different amino acid is coded for </li></ul><ul><li>protein function may or may not be affected </li></ul><ul><li>Sickle cell anemia is a result of a missense mutation. </li></ul>
  5. 6. Sickle Cell Anemia Heterozygous or homozygous for sickle cell anemia?
  6. 7. Nonsense Mutations <ul><li>nonsense mutation – nucleotide sequence is changed such that an amino acid is replaced with an early stop codon </li></ul><ul><li>short proteins are made; usually digested by proteases </li></ul><ul><li>nonsense mutations usually are lethal </li></ul>
  7. 8. Type of DNA Change: Point Mutations <ul><li>point mutation – nucleotide changes where one base pair (bp) is replaced by another bp </li></ul><ul><li>Point mutations are also known as substitution mutations . </li></ul>
  8. 10. Type of DNA Change: Frameshift Mutation <ul><li>frameshift mutations – changes in the DNA sequence which modify the translation reading frame </li></ul><ul><li>Deletions – removal of one or more NTs </li></ul><ul><li>Insertions – addition of one or more NTs </li></ul>
  9. 12. Type of DNA Change: Chromosomal Mutations <ul><li>Sections of chromosomes can break off and reattach abnormally. </li></ul><ul><li>Translocation mutations </li></ul><ul><li>Inversion mutations </li></ul>
  10. 13. Chromosomal Mutation <ul><li>translocation mutations – large portions of DNA are exchanged </li></ul>
  11. 14. Translocation
  12. 15. Down Syndrome
  13. 16. Chromosomal Mutations <ul><li>inversion mutations – sections of a chromosome are reversed </li></ul>
  14. 17. Crossing Over
  15. 19. Fixing Mutations <ul><li>Enzymes are able to recognize when: </li></ul><ul><ul><li>nitrogenous bases are missing </li></ul></ul><ul><ul><li>nitrogenous bases are fused together </li></ul></ul><ul><li>These mutations are detected and fixed by DNA polymerase I. </li></ul>
  16. 20. Fixing Mutations <ul><li>Enzymes recognize when bases are incorrectly paired together. </li></ul><ul><li>These mismatch mutations are fixed by DNA polymerase III. </li></ul><ul><li>How does the enzyme know which strand has the correct base pair? </li></ul><ul><li>The original template strand is methylated. </li></ul>
  17. 22. Causes of Mutations <ul><li>spontaneous errors due to enzymes </li></ul><ul><li>induced errors due to mutagenic agents </li></ul><ul><ul><li>UV radiation </li></ul></ul><ul><ul><li>X-rays </li></ul></ul><ul><ul><li>chemical (Agent Orange) </li></ul></ul>
  18. 23. Spontaneous Errors <ul><li>guanine may react with water to form 8-oxo guanine </li></ul><ul><li>8-oxo G pairs up with adenine during replication </li></ul>

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