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Mutations

DNA mutations can have varying effects, including no effect, harmful outcomes, or beneficial changes. The main types include silent mutations, missense mutations, and nonsense mutations. Silent mutations cause no change in protein function while missense mutations result in altered amino acids, potentially leading to conditions like sickle cell anemia. Nonsense mutations introduce early stop codons, usually resulting in nonfunctional proteins. Mutations can arise from spontaneous errors or exposure to mutagens. Understanding these changes is essential for genetics and medical research.

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Mutations

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  1. Mutations

  2. Mutations • mutations – errors in the DNA • can have a bad resultant effect • can have no effect • can have a positive resultant effect Mutations are usually not an issue because we have two copies of each gene.

  3. Mutations Changes in DNA result in: • silent mutations • missense mutations • nonsense mutations

  4. Silent Mutations • silent mutation – has no effect on the function of the cell; sequence of amino acids is not affected • often found in the non-coding regions (introns) • If introns in mRNA are spliced out, then the mutation never surfaces • Some amino acids can be coded for by multiple codons. (referred to as redundancy in the genetic code • It is possible that one change in the base pair will still produce the same amino acid

  5. Missense Mutation • missense mutation – nucleotide sequence is changed such that a different amino acid is coded for • protein function may or may not be affected Sickle cell anemia is a result of a missense mutation.

  6. Wild-type hemoglobin DNA Mutant hemoglobin DNA In the DNA, the mutant template strand has an A where the wild-type template has a T. 3 5 3 5 T T C A T C mRNA mRNA The mutant mRNA has a U instead of an A in one codon. G A A U A G 5 3 5 3 Normal hemoglobin Sickle-cell hemoglobin The mutant (sickle-cell) hemoglobin has a valine (Val) instead of a glutamic acid (Glu). Val Glu Sickle Cell Anemia

  7. Sickle Cell Anemia

  8. Nonsense Mutations • nonsense mutation – nucleotide sequence is changed such that an amino acid is replaced with an early stop codon • short proteins are made; usually digested by proteases • nonsense mutations usually are lethal

  9. DNA: 5' - ATG ACT CAC CGA GCG CGA AGC TGA - 3‘ 3' - TAC TGA GTG GCT CGC GCT TCG ACT - 5' mRNA: 5' - AUG ACU CAC CGA GCG CGA AGC UGA - 3' Protein: MetThrHisArgAlaArgSer Stop DNA: 5' - ATG ACT CAC TGA GCG CGA AGC TGA - 3‘ 3' - TAC TGA GTG ACT CGC GCT TCG ACT - 5‘ mRNA: 5' - AUG ACU CAC UGA GCG CGU AGC UGA - 3‘ Protein: MetThrHis Stop Template Strand Mutation

  10. Type of DNA Change:Point Mutations • point mutation – nucleotide changes where one base pair (bp) is replaced by another bp Point mutations are also known as substitution mutations.

  11. Types of DNA Change • Point Mutation (Base-Pair Substitution) • Frameshift Mutation • Chromosomal Mutation

  12. Silent mutation

  13. Type of DNA Change: Frameshift Mutation • frameshiftmutations – changes in the DNA sequence which modify the translation reading frame • Deletions– removal of one or more NTs • Insertions– addition of one or more NTs

  14. Type of DNA Change:Chromosomal Mutations Sections of chromosomes can break off and reattach abnormally. • Translocation mutations • Inversion mutations

  15. Chromosomal Mutation • translocation mutations – large portions of DNA are exchanged

  16. Translocation

  17. Chromosomal Mutations • inversion mutations – sections of a chromosome are reversed

  18. Causes of Mutations

  19. Causes of Mutations • spontaneous errors due to enzymes • induced errors due to mutagenic agents • UV radiation • X-rays • chemical (Agent Orange) • transposable elements

  20. Spontaneous Errors • guanine may react with water to form 8-oxo guanine • 8-oxo G pairs up with adenine during replication

  21. Visualization of Mutations

  22. Transposable Elements • some DNA sequences naturally move themselves around the genome - transposons

  23. Classwork/Homework • Pg. 263 #1-8

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