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DNA Mutations

DNA Mutations. Unit 5: Molecular Genetics Chapter 12-4, pages 307-308. Mutants…. Nature isn’t always perfect! What happens when a MISTAKE is made in DNA Replication or RNA Transcription?. Mutants…. What is a mutation?. Cells can make mistakes in replicating or transcribing their own DNA

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DNA Mutations

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  1. DNA Mutations Unit 5: Molecular Genetics Chapter 12-4, pages 307-308

  2. Mutants… • Nature isn’t always perfect! • What happens when a MISTAKE is made in DNA Replication or RNA Transcription?

  3. Mutants…

  4. What is a mutation? • Cells can make mistakes in replicating or transcribing their own DNA • Mutations are changes in the genetic material (from a Latin word meaning “to change”)

  5. DNA Mutations • To illustrate DNA mutations, we’re going to use this DNA / mRNA / amino acid sequence: TAC TTC AAA CCC CGT AAC ATT AUGAAGUUU GGG GCA UUG UAA Met – Lys – Phe – Gly – Ala – Leu -SXP

  6. Point Mutations • Point mutations are single-base changes in a gene’s DNA sequence. • These include: -missense mutations -nonsense mutations -silent mutations

  7. Point Mutations: missense mutation • Missense mutations result in a single amino acid change within a protein. • This DOES change the resulting protein.

  8. change! Point Mutations: missense mutation TAC TTC AAA CCC CGT AAC ATT AUG AAG UUU GGG GCA UUG UAA Met - Lys - Phe -Gly- Ala - Leu- TAC TTC AAA TCC CGT AAC ATT AUG AAG UUU AGG GCA UUG UAA Met - Lys - Phe - Ser - Ala - Leu-STP

  9. Point Mutations: nonsense mutation • Nonsense mutations create a premature stop codon, causing the protein to be shortened. • This DOES change the resulting protein.

  10. change! Point Mutations: nonsense mutation TAC TTC AAA CCC CGT AAC ATT AUG AAG UUU GGG GCA UUG UAA Met - Lys - Phe -Gly- Ala - Leu-STP TAC TTC AAA CCC CGT ATC ATT AUG AAG UUU GGG GCA UAG UAA Met - Lys - Phe - Gly- Ala - stop-STP

  11. Point Mutations: silent mutation • Silent mutations change the DNA sequence, but not the amino acid sequence. • This DOES NOT change the resulting protein, and has no effect on an organism.

  12. NO change! Point Mutations: silent mutation TAC TTC AAA CCC CGT AAC ATT AUG AAG UUU GGG GCA UUG UAA Met - Lys - Phe -Gly- Ala - Leu-STP TAC TTC AAA CCA CGT AAC ATT AUG AAG UUU GGU GCA UUG UAA Met - Lys - Phe - Gly- Ala - LeuSTP

  13. Frameshift Mutations • Frameshift mutations result from the insertion or deletion of one or more bases into or from the DNA sequence. • This alters the grouping of nucleotides into three-base codons, causing a shift in the “reading frame” during translation. • The resulting protein is usually nonfunctional.

  14. we’re going to delete this “A” Frameshift Mutations TAC TTC AAA CCG CGT AAC ATT AUG AAG UUU GGG GCA UUG UAA Met - Lys - Phe -Gly- Ala - Leu-STP TAC TTC AAC CGC GTA ACA TTT AUG AAG UUGGCG CAU UGU AAA Met - Lys - Leu- Ala - His - Cys- Lys

  15. What causes mutations? • Many mutations are due to mistakes made in replication, or transcription. • Mutagens are things that can cause a change in DNA sequences. All of these mutagens can damage your DNA: • UV light • radiation • exposure to chemicals

  16. How often do mutations occur? • Mutations are rare events; the average rate of mutation is one in a million replications. • However, since DNA replication and transcription takes place daily in your body, you DO have mutations in your DNA sequence!

  17. The Pros and Cons of Mutations… • PRO: mutations are the source of genetic variability in a species! • CON: mutations can disrupt normal biological activity, resulting in a genetic disorder or cancer.

  18. Example 1 – Fish Odor Syndrome The Orkney Islands, Scotland

  19. Example 1 – Fish Odor Syndrome • First mentioned in Shakespeare’s The Tempest (re: Caliban) • Body constantly secretes powerful odor of rotting fish or garbage • Highest frequency of people with this condition isolated on Orkney Islands

  20. Example 1 – Fish Odor Syndrome • Fish odor syndrome (aka trimethylaminuria) is the result of a mutation in the gene encoding the FMO3 enzyme • Without this liver enzyme, body fails to break down a smelly substance called trimethylamine (TMA), an ordinary byproduct of digesting foods high in protein • Extremely rare condition; must inherit a mutated gene from BOTH mother and father to have the condition

  21. Example 2 – Sickle Cell Anemia • Sickle cell anemia is the result of a point mutation.

  22. Example 2 – Sickle Cell Anemia

  23. Example 2 – Sickle Cell Anemia

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