Mutations
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Biochemistry from Dr. Dhiraj J. Trivedi, SDM College of Medical Sciences and Hospital,Dharwad, India
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Mutations
- 1. Mutations Errors in writing or reading of DNA Cancer == Cancel Miss == Kiss Walk == Talk She == He
- 2. The “Central Dogma” DNA RNA Protein How do we move information from DNA to Protein Transcription Translation Replication Where we make error
- 3. Involves processes • REPLICATION – synthesis of DNA from DNA • Transcription – Synthesis of RNA from DNA • Translation – Synthesis of protein from the information present on mRNA. • Reverse transcription – Synthesis of DNA from RNA
- 4. What causes error (Mutations)? 1. Proof reading during DNA replication. DNA polymerase corrects mismatch 2. DNA repair if faulty. After DNA replication any error corrected by repair enzyme 3. DNA recombination error Chromosome cross over and recombination if defective
- 5. What causes error (Mutations)? 4. Chemical mutagens Chemical modification of nitrogen bases 5. Irradiation of UV light or ionizing radiations 6. Spontaneous mutations Without any underlying cause
- 6. Mutations defined … • Change in the nucleotide sequence of gene AAA GGA CCU UUA AUA GGA CCU UUA • Either one or more • UUA AUG CCG UAA UUA AUG CCG UAG Tyrosine Termionation Lysine Isoleucine
- 7. Mutations Point mutations Frame shift Mutations Transition Transversion Insertion Deletion
- 8. Single point mutations Single nucleotide (base) of gene is changed Transversions • Purine base is replaced by pyrimidine base or vice versa Transitions • Purine base is exchanged by purine base or vice versa Mutations types A C G T A G C T
- 9. mutation may be Frame shift mutation: Deletion type • Deletion of single nucleotide from coding strand • Reading frame in mRNA sifted • Translation affected Insertion type • Insertion of one or more nucletide in the coding strand • Additonal base added • Coding sequence changes AUG GCC UCU UGC AAA … AUG GCC CUU GCA AAG … AUG GCC UCU UGC AAA … AUG GCC UCU UGA UAG …
- 10. Result of point mutations • Single point mutation when transcribed in mRNA ---- • Molecule contain changed base in codons • When translated • Normal protein may be produced --- degeneracy of code • Valine on β67 replaced by alanine -- forms HB sydney • Altered protein produced --- change in code • HB A β chain 6th Glutamate --- replaced by Valine -- HB S
- 11. Effects of mutation may be Silent Goes unnoticed or without effect Protein may function normal – Acceptable -- HBC, HBD Silent mutation
- 12. Effects of mutation may be Missense Wrong amino acid incorporated Protein may function normal – Acceptable -- HBC, HBD Protein may function at low activity – partially Acceptable HB S Protein non functional --- unacceptable -- HB M, Missense Mutations
- 13. Effect of mutation may be Nonsense • Normal codon converted to termination codon • Shortened β chain of HB, prematured termination of protein synthesis • Protein non functional --- unacceptable Nonsense mutation:
- 14. Whoops! See what happens when your genes don’t work right! Any Questions??