Notes April 22

Mutational hotspots: Areas in the DNA that are more prone to mutation than others. (ex: Repetative sequences: slipped strand mispairing; stretches with lots of T's: UV light can cross-link two or more adjacent thymines called a thymine dimer or trimer.)

Mutagens: Any chemical or treatment that induces mutations. Causes DNA sequence to change.
A.) Depurination via hydrolysis: Water; Purines are easily removed from sugar-phosphate backbone by hydrolysis. They aren't lasting mutations that are passed on from generation to generation. The AP repair system replaces missing purines, but if it is not successful in doing so, then it will just put a random base where there is none to pair with.
B.) Oxidation: Addition of oxygen to a base, which yields a change in a base's H-bonding traits.
C.) Base Analogs: Chemicals similar in structure to bases. When DNA replicates it may have a base analog incorporated with the new strand. (Ex: Thymine=Bromouracil: keto(binds with A) and enol(binds with G))
D.) Alkylating Agents: Any chemicals that add an Alkyl group to the DNA bases. It stops the altered DNA from being replicated.
E.) Intercalating Agents: Flat, planar carbon ring-like structures that smish between bases in double stranded DNA. (ex: Ethidium Bromide, Acridine orange)
F.) Radiation: Ultraviolet light: Inducing Thymine dimers. and Ionizing Radiation: X-rays, gamma rays; They induce mutations by causing breaks in the phosphodiester backbone of DNA. When breaks are not patched up it can cuase the destruction of entire chromosomes. Breakages are most likely to occur during replication.

DNA Repair Mechanisms:
A.) Mismatch repair: Recognize where there is wrong base pairing. Then kink the strand. Find older strand (methylated strand) and it snips the DNA strand that is non-methylated on either side of the mismatch. An enzyme degrades the swatch by a DNA polymerase and then a DNA ligase patches the breaks in that DNA strand.

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