15BIS101F2013MutatLect15

Since gross since gross mutations can involve

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: rame-shift mutations in the gene. This BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 36 Molecular Mechanism of Mutation Physical Mutagens BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 37 Physical Mutagens Herman Muller discovered Herman the first mutagen in the form of X-rays. In 1927, Muller demonstrated that up to a point, the frequency of mutations in certain genes of Drosophila was directly Drosophila proportional to the X-ray dose. Because the high energy of XBecause rays, most mutations involved rays, chromosome breakage or gross mutations. Since gross Since gross mutations can involve thousands or millions of base pairs, they are not has helpful for the fine genetic analysis. for ­ Mutagenesis (X-ray dose) BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 38 Physical Mutagens (Ultraviolet Light) One physical mutagen that is One capable of creating point mutations is ultraviolet light (UVA, 320is 400nm; UVB, 290-320nm). 400nm; Although UV is much less energetic than X-rays, it is still a very potent mutagen because the bases of DNA absorb energy in the UV wavelength range (260nm). Strong UV irradiation can produce chromosomal breaks, however, lower doses can produce permenant photoproducts called pyrimidine dimers. Dimerization pyrimidine Dimerization can occur between adjacent C and C, U and U, C and U, but T and T (thymine dimers) are the most common photoproduct in UV irradiated DNA. ­ BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 39 UV Induced Pyrimidine Dimers Pyrimidine dimers become Pyrimidine mutagenic when they go uncorrected. DNA polymerase does not recognized pyrimidine dimers as good templates and will either stall at the dimer or delete or add a nucleotide. Therefore, UV irradiation is useful in producing point mutations of the single nucleotide insertion or deletion. The lac UV5 promoter mutation was created with UV irradiation. created BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez 40 DNA Repair (critical for survival) Maintaining the sequence integrity of DNA is critical Maintaining for the survival and fitness of an organism. For this reason, nature has evolved a number of mechanism for repairing various types of DNA damage. for Direct reversal of damage (photolase, alkyltransferase Excision-repair pathways (uvrA, uvrB and uvrC) Specific excision repair (DNA glycosylases) GO system (mutM, mutY and mutT) Post-replication or mismatch repair (adenine methylase) Recombination repair (recA) BIS101­001, Spring 2013—Genes and Gene Expression R.L. Rodriguez ©2013 BIS101­001, Spring 2013—Genes and Gene...
View Full Document

This note was uploaded on 02/12/2014 for the course BIS 101 taught by Professor Simonchan during the Spring '08 term at UC Davis.

Ask a homework question - tutors are online