Finals - Mutation Flashcards
any heritable change in the DNA
mutation
importance of mutation
- may have deleterious or advantageous consequences to an organism (or its descendants)
- genetic studies
- major source of genetic variation which fuels evolutionary change
Types of mutations based on no. of bases changed
- point mutation
- multiple mutation
involves a single base pair
point mutation
involves two or more bp
multiple mutation
point mutations
- base substitution
- framshift mutation
two types of base substitution
- transition
- transversion
purine to purine; pyrimidine to pyrimidine
transition
purine to pyrimidine; pyrimidine to purine
transversion
two types of frameshift mutation
- base addition
- base deletion
frameshift to the left
base addition
frameshift to the right
base deletion
Types of mutation based on consequences of change in terms of amino acid sequence affected
- silent mutation
- neutral mutation
- missense mutation
- nonsense mutation
results in the same amino acid
silent mutation
resutls in substitution of an amino acid with similar chemical properties
neutral mutation
results in substitution of a different amino acid
missense mutation
results in a stop codon
nonsense mutation
process of altering an organism’s genetic information, which can occur naturally or through a variety of experimental technique
Mutagenesis
Two types of mutagenesis
- spontaneous
- induced
- occurs as a result of natural processes in cells
- could be due to evasion of proofreading by DNA pol I
spontaneous mutagenesis
occurs as a result of interaction of DNA with an outside agent or mutagen
induced mutagenesis
anything that causes mutation
mutagen
Different spontaneous mutations
- uncorrected mismatches
- tautomerization
- replication slippage
- spontaneous depurination
- spontaneous deamination
Errors during DNA synthesis, if uncorrected, give rise to mutations in the next round of replication.
uncorrected mismatches
- proton shift
- bases of DNA are capable of existing in two forms by which they interconvert
- occurs when the tautomeric form of a base pairs with a non-complementary base, which becomes fixed in the DNA sequence after replication
tautomerization
Two types of tautomerization
- keto (C=O) <-> enol (C=OH)
- amino (NH2) <-> imino (NH)
DNA base pairing in tautomeric state
- A-C
- T-G
- in template DNA with short repeated sequences
- results in frameshift mutation
- happens when either template/new DNA loops out
replication slippage
cause of replication slippage
when either template/new DNA loops out
looping out of new strand
one base insertioin on new strand
looping out of template strand
one base deletion on new strand
- loss of purine bases (adenine and guanine) from DNA.
- N-glycosyl bond to deoxyribose is broken by hydrolysis, leaving the DNA’s sugar–phosphate chain intact, producing an abasic site
Spontaneous Depurination
site formed in spontaneous depurination
apurinic site
- hydrolytic removal of amino (-NH2) groups from guanine (most common), cytosine or adenine
- Oxidative damage of deoxyribose with any base, but most commonly purines
Spontaneous Deamination
bases where deamination can occur
- guanine
- cytosine
- adenine
Three types of induced mutations
- chemical mutagens
- physical mutagens
- transposable elements
chemical mutagens
- base analogs
- base-modifying agents
- intercalating agents
physical mutagens
- UV radiation
- ionizing radiation
- heat
Three different ways mutagens can cause mutations
- act as base analogs
- react directly w/ DNA
- act directly on DNA
- bases that are similar enough to the standard bases to be incorpoated into nucleotides during DNA replication
- cause point mutations
base analogs
example of base analogs
- 5-bromouracil
- 2-aminopurine
5-bromouracil
analog of T
2-aminopurine
analog of A
5-bromouracil keto form binds with ?
adenine
5-bromouracil enol form binds with ?
guanine
2-aminopurine amino form binds with ?
thymine
2-aminopurine imino form binds with ?
cytosine
chemicals that actually change the chemical structure of certain nucleotides (bases) in DNA causing them to mis-pair
Base-modifying agents
Different base-modifying agents
- deaminating agents
- hydroxylating agents
- alkylating agents
example of deaminating agents
- nitrous acid (inorganic air pollutant)
- sodium bisulfite (food additive)
- sodium dioxide (burning coal and petroleum)
deaminate A, C, G
nitrous acid
deaminate C
- sodium bisulfite
- sodium dioxide
addition of OH
hydroxylating agents
add OH to cysteine
hydroxylamine
alkylate guanine causing frameshift mutation
- ethylmethane sulfonate (EMS)
- methylmethane sulfonate (MMS)
where are ethylmethane sulfonate (EMS) and methylmethane sulfonate (MMS) found
air polluted with cigarette smoke
nitrous acid effect on guanine
becomes xanthine (pairs w/ C)
nitrous acid effect on cytosine
becomes uracil (pairs w/ A)
nitrous acid effect on adenine
becomes hypoxanthine (pairs w/ C)
hydorxylamine effect on cytosine
becomes hydroxylaminocytosine (binds w/ A)
methylmethane sulfonate (MMS) effect on guanine
becomes O^6-methylguanine (pairs w/ T)
- thin, plate-like hydrophobic molecules that insert between adjacnt base pairs
- distortions in the helix and no unwinding
intercalating agents
where do intercalating agents insert
between adjacent base pairs
eg. of intercalating agents
- ethidium bromide
- proflavin
- acridine orange
- benzypyrene
intercalating agent on template strand
frameshift mutation due to insertion of one base pair
intercalating agent on new strand
intercalating agent lost in replication of template strand
- dimerization of adjacent pyrimidine bases
- 6-4 lesion
- cytosine transformation to its imine tautomer
- covalent joining of complementary strands due to interchain dimerization
UV radiation of 260 nm (UVC)
dimerization of adjacent pyrimidine bases
cyclobutyl dimer
eg. of cyclobutyl dimer
thymine dimer
covalent bond of thymine dimer
- C6-C6
- C5-C5
(6-4) lesion
6-4 photoproduct
what happens in (6-4) lesion
C6 covalently bonds with C4
effect of (6-4) lesion
- distors helix as DNA bases are pulled closer
- extensive cleavage of H-bonds
- inhibits advance of replication fork
covalent joining of complementary strand is due to ?
interchain dimerization
Effects of UV radiation
- dimerization of adjacent pyrimidine bases
- (6-4) lesion
- cytosine to imine tautomer (pairs w/ A)
- covalent joining of complementary strands due to interchain dimerization
- x-rays, gamma rays, high speed e- or alpha paricles
- fast moving neutrons
- more potent than UV
ionizing radiation
what are the ionizing radiations
- x rays
- gamma rays
- high speed e-/alpha particles
effects of ionizing radiation
- formation of rare tautomeric enols
- removal of cytosine from DNA
- favored formation of the imine tautomer of C
- production of ss and ds breaks on DNA backbone
- stimulates water-induced cleavage of the β-Nglycosidic bond
- results in baseless site causing frameshift mutation to the right
- not normally mutagenic because cells have effectiv system for repairing nicks
heat
what is resulted in heat
baseless sites (apurinic/apyrimidinic site)
why is heat not normally mutagenic
due to effective system for repairing nicks