1. Mutations Natural and Artificial Mutations

2. Mutations There are 2 classes of mutations Nucleotide mutations occur when 1-4 nucleotides are altered, added or removed as a result of damage or errors in replication Transpositions occur when entire sections of DNA “jump” to a different location in the DNA, disrupting genes

3. Examples of nucleotide mutations Point Mutations – one nucleotide is altered Silent Mutation: CTC to CTT – no change since both codons code for glutamic acid Missense Mutation: CTC to CTA replaces glutamic acid with aspartic acid in hemoglobin since they are functionally similar amino acids, the protein is not greatly affected and the mutation introduces a variation in the species CTC to CAC replaces glutamic acid with valine Valine is hydrophobic and results in clumping of hemoglobin, resulting in sickle cell anemia

4. Sickle Cell Anemia

5. Nucleotide Mutations A point mutation could also result in the production of a stop codon in the middle of a gene If this occurs in an essential protein, such as hemoglobin, the mutation is lethal and is called a nonsense mutation Frameshift mutations are also normally lethal – the insertion or deletion of a nucleotide shifts the entire reading frame and every codon is altered

6. Transposons

8. Approximately 50 % of the human genome is made up of transposons They can “jump” from one location to another, or they can copy themselves first, and the copy jumps Transposons can cause mutations by inserting themselves into exons, or by taking exons with them; “shuffling” the genetic deck Transposons can jump to a promoter region and either turn off or turn up transcription

9. Transposons

10. Artificial Mutation

11. UV Radiation UV radiation produces covalent bonds between adjacent thymine base pairs These dimers block replication by DNA polymerase Cells can repair the damage by removing the damaged section on one side of the helix DNA polymerase and DNA ligase complete the repair If the repair is done incorrectly, a mutation results http://highered.mcgraw-hill.com/sites/0072556781/student_view0/chapter11/animation_quiz_5.html

12. Chemical Mutagens Base analogs Chemicals that have a very similar structure to thymine, uracil, adenine, cytosine or guanine Example: 5’bromouracil Base analogs generally result in point mutations

13. Chemical Mutagens Acridine dyes These chemicals have a positive charge so they bind to the negatively charged DNA They insert between base pairs and cause frameshift mutations Examples; nitrous acid and hydrazine

14. Chemical Mutagens Alkylating agents Can transfer methyl groups, ethyl groups, bond with phosphate groups This can result in any type of mutation, including the lethal breakage of the DNA sugar-phosphate backbone They are actually used as chemotherapy in the treatment of cancer, destroying the cancerous cells’ DNA Image from Science Daily