Mutations Flashcards
base substitutions
Transitions: purine to purine or pyrimidine to pyrimidine
Transversion: purine to pyrimidine or pyrimidine to purine
insertions and deletions
1 or 2 nucleotide insertions cause frameshift mutations
tautomeric shifts
movement of hydrogen atoms
results in base movements
expanding nucleotide repeats
increase in number of copies of a set of nucleotides
Functional effects of mutations
-missense: different protein coded
-nonsense: stop codon
-silent: no effect, codes for same protein
-forward mutation: normal to mutant
-reverse mutation: mutant to normal
-neutral: missense where amino acid is changed to a similar chemical type
-loss-of-function: complete or partial loss of normal protein function
-gain-of-function: produce a protein whose function normally is not present
-conditional mutation: expressed only in certain conditions
suppressor mutations
second site mutation that hides the effect of the first
intragenic: on same gene
intergenic: on different genes
mutation rates and factors
-DNA in nucleosomes have fewer mutagens
-frequency, probability, and detection
spontaneous replication errors
tautomeric shifts
-positions of hydrogen atoms in bases change
mispairing due to other structures
-arise through wobble, allows different bases to bond
incroporated errors and replicated errors
-when a base substitution causes a mis-paired base to incorporate into new strand
-deletions and insertions
-can arise during replication or crossing overi
Sponetaneous chemical changes
depurination
-loss of purine from breakage of covalent bond between purine and 1’carbon of the sugar
deamination
-loss of amino group, from cytosine which gives rise to Uracil which pairs with adenine during replication which pairs with T
-result is C to T
methylated cytosine
-converts to thymine
chemically induced: base analogs
chemicals with structures similar to the AGCT
-5BU: analog of thymine, pairs with adenine, result is A to G
-2AP: analog of Adenine, mis-pairs with cytosine, T to C
chemically induced: alkylating agents
mutagens that add methyl or ethyl groups
-Ethylmethylsulfonate (EMS) and Mustard gas
chemically induced: deaminating chemicals
addition to spontaneous deamination
Nitrous. acid:
-can change cytosine to thymine
-can change adenine into hypoxanthine which can base pair with cytosine
-can change guanine into xanthine which can base pair with thymine
chemically induced: hydroxylamine
-adds hydroxyl group to cytosine, forms hydroxylaminocytosine
-increases occurence of rare tautomer that pairs with adenine
chemically induced: oxidative radicals
-reactive forms of oxygen
-produced through aerobic metabolism or chemicals and radiation
chemically induced: intercalating agents
examples: ethidium bromide, acridine orange, dioxin, proflavin
-sandwhich between adjacent bases
-distorts helix
-causes insertions and deletions
radiation
X-Rays:
-dislodge electrons from atoms
-breaks phosphodiester bonds, leads to double stranded breaks
UV:
-pyrimidine bases absorb UV light
-induces chemical bonds between two adjacent pyrmidine molecules on same strand
-thymidine dimers most frequent
