Topic 1C - Part 2 Flashcards
mutagen
an agent that increases the probability of mutation
single-stranded break in DNA backbone
X-rays -breaks can occur in just one strand of DNA or both
cross-linked thymine bases
UV light- forms thymine dimers through covalent bonds, causes double helix to become pinched and weakens the T-A base pairing
missing base
rate increases with age, or exposure to oxidizing agents such as bleach or hydrogen peroxide- spontaneous loss is most common, result of interaction between DNA and normal metabolic by-products
mis-paired base
chemically damaged bases (interferes with ability to form hydrogen bonds with a complement), mimic molecules incorporated as bases, ex. caffeine mimics a purine base
bulky side groups attached to a base
chemicals that are highly reactive (mutagenic)-ex. tobacco smoke. chemicals can also cause the insertion or deletion of several nucleotides
what can repair breaks in the sugar-phosphate backbone?
DNA ligase, uses ATP energy to join 3’hydroxyl to 5’phosphate (different ones for single vs. double strand break)
double-stranded DNA breaks often result in:
chromosomal rearrangements because they are less likely to be repaired than single-stranded breaks
how are ligases an important tool in molecular biology research?
allows DNA molecules from different sources to be joined to produce recombinant DNA
what corrects mis-paired bases?
proofreading function of DNA polymerase-mispaired nucleotide is removed immediately after incorporation and replaced by correct nucleotide and postreplication mismatch repair
postreplication mismatch repair
the correction of a mismatched base in a DNA strand by cleaving one of the strand backbones, degrading the sequence with the mismatch, and resynthesizing from the intact DNA strand (back-up for mismatched bases)
base excision repair
a specialized repair system in which an incorrect DNA base and its sugar are both removed and the resulting gap is repaired by a polymerase
nucleotide excision repair
the repair of multiple mismatched or damaged bases across a region; a process similar to mismatch repair, but over a much longer piece of DNA (REMOVES THE ENTIRE DAMAGED SECTION OF A STRAND AT ONCE), sometimes thousands of nucleotides, can also remove bulky side groups and thymine dimers
DNA repair mechanisms can reduce:
the rate of mutation to a level that is compatible with life.
DNA repair mechanisms do not catch all mistakes, the result is:
genetic variation, the raw material of evolution
