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Difference between spontaneous and induced mutations + sources for each?
- Spontaneous: Replication errors, base modifactions (tautomeric shifts), transposable elements
- Induced: DNA damage from chemicals and radiation, organisms have DNA repair systems to counteract DNA damages
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Various types of mutations
- Transitions: purine for purine (A -> G)
- Transversions: purine for pyrimidine (A -> C)
- Deletion/insertion of more than one base
- Major alteration in chromosomal structure
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Various sources of spontatious mutations
- DNA Polymerase occasionally inserts incorrect nucleotides
- Tautomeric shifts: allow noncomplementary basepairing (A-C)
- Deamination: amino group in C or A is converted to uracil (A-T converted to G-C)
- Depurination: loss of one nitrogenous base in an intact double-helical DNA molecule
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UV Radiation: what change to the DNA do they cause, and how are they repaired
- Cause pyrimidine dimers (typically thymine) that distort DNA conformation.
- Photoreactive repair (prokaryotes): uses blue light to repair
- Nucleotide excision repiar (euk): nuclease excises lesion and gap is filled/repaired
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Ionizing radiation
- X rays, gamma rays, cosmic rays
- Transofrms stable molecules into free radicals which alter DNA
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Ames test
- Salmonella typhimurium used to reveal mutagenic properties of substances.
- Bacteria are His- and grown on a medium that includes His. Anything that grows has undergone mutation. Spontaneous reverts are used as a control
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