Genetic Mutations and DNA Repair

Question 1

what is a mutation?

Answer 1

a heritable change in an organism’s genetic material that may alter the phenotype of the organism

Question 2

what is a mutant?

Answer 2

an organism that carrier one or more mutations in their genetic material

Question 3

how are mutations and evolution related?

Answer 3

mutation is the source of all genetic variability
natural selection preserves the best adapted
recombination between homologous chromosomes creates more variability

Question 4

what are the types of genetic mutations?

Answer 4

SOMATIC: will not be transmitted to progeny
GERM: transmitted to progeny via GAMETE

Question 5

what is transition mutation?

Answer 5

replaces a pyrimidine with another pyrimidine or a purine with a purine

SAME

Question 6

what is a transversion mutation?

Answer 6

replaces a pyrimidine with a purine or vice versa

DIFFERENT

Question 7

what are frame shift mutations?

Answer 7

insertion or deletion, shifting the reading frame
mutant DNA –> mutant mRNA –> WRONG PROTEINS

Question 8

what are TAUTOMERIC shifts?

Answer 8

a rare REVERSIBLE change in the location of a hydrogen atom on a NT

=O (keto) –> -OH (enol)
-NH2 (amino) –> =NH (immino)

can cause A=C pairs and GT pairs (triple bond)

Question 9

how many mutant daughter strands will you get in the second progeny of a tautomeric shift?

Answer 9

1/4

Question 10

what are expanding nucleotide repeats?

Answer 10

repeats in a triplet codon
(ex. supposed to be 30 repeats, now there are 50)
caused by a hairpin structure

Question 11

what is a MISSENSE mutation?

Answer 11

a base substitution that results in an AA change in the protein

Question 12

what is a NONSENSE mutation?

Answer 12

base substitution that codes for a STOP codon

Question 13

what is a SILENT mutation?

Answer 13

a base substitution where the changes in the codon still specify the SAME AA

Question 14

what is a loss of function mutation?

Answer 14

results in complete or partial loss of normal protein function

Question 15

what is a gain of function mutation?

Answer 15

produces a protein or a gene product who’s function is not normally present

Question 16

what is a conditional mutation?

Answer 16

expressed under CERTAIN (environmental) conditions

Question 17

what is a lethal mutation?

Answer 17

causes premature cell death

Question 18

what is a SUPPRESSOR mutation?

Answer 18

mutation at a SECOND SITE that hides or suppresses the effect of the first mutation

INTRAGENIC = same gene
INTERGENIC = different gene

NOT a reverse mutation

Question 19

what factors affect mutation rates?

Answer 19

DNA wrapped around HISTONES have FEWER mutations

frequency, probability, detection

Question 20

describe mispairing due to other structures

Answer 20

shifts in the helix or PROTONSTION of bases can allow DIFFERENT BASES TO BOND

can arise from WOBBLE (nonstandard base pairing in 3rd codon)

Question 21

what are INCORPORATED errors?

Answer 21

base substitution causes a mis-paired base to be incorporated into the strand
repair system cannot correct this

Question 22

what can cause insertion or deletion mutations?

Answer 22

crossing over
strand slippage (forms a loop in template OR new strand)

Question 23

what is depurination?

Answer 23

loss of a purine base from a NT
breakage of covalent bond between purine base a 1’C atom of sugar
A is most often incorporated into the base, causing a permanent mutation

Question 24

what is demaination?

Answer 24

cytosine loses its NH2 group and BECOMES URACIL and will pair with ADANINE (C–>T transition)

methylated cytosine will become THYMINE (C–>T transition)

Question 25

what are BASE ANALOGS?

Answer 25

chemicals with similar structures to the 4 NTs 5-BROMOURACIL is an analog of thymine that can pair with guanine (A --> G transition) 2-AMINOPURINE is a base analog of adenine that mis pairs with CYTOSINE (T --> C transition)

Question 26

what are ALKYLATING AGENTS?

Answer 26

add METHYL or ETHYL groups to bases ex. ETHYLMETHYLSULFONATE (EMS) and MUSTARD GAS adds ethyl group to guanine, causes it to pair with thymine (G-->A transition) adds an ethyl group to thymine, causes it to pair with guanine (T-->C transition)

Question 27

what are DEAMINATING chemicals

Answer 27

removes a NH2 group NITROUS ACID causes transition mutations

Question 28

what is HYDROXYLAMINE?

Answer 28

adds hydroxyl groups to cytosine increased occurance of tautomer that pairs with adenine C-->T transition

Question 29

what are OXIDATIVE RADICALS?

Answer 29

reactive forms of oxygen produced by metabolism causes TRANSVERSION mutations REMEMBER: oxidatiVe, transVersion (the Vs go together)

Question 30

what are INTERCALATING agents?

Answer 30

ETHIDIUM BROMIDE, ACRIDINE ORANGE, DIOXIN, PROFLAVIN sandwiches between base pairs distorts helix causes FRAMESHIFT mutations

Question 31

how do X rays cause mutations?

Answer 31

produce IONIZING radiation dislodge electrons from atoms produce free radicals breaks phosphodiester bonds --> double stranded breaks

Question 32

how does UV cause mutations?

Answer 32

PYRIMIDINES absorb UV light induces chemical bond between two adjacent pyrimidines (STOP signal) causes thymidine dimers

Question 33

what are the two general features of DNA repair?

Answer 33

complimentary strand acts as a TEMPLATE for the one being repaired DNA repair has REDUNDANCY

Question 34

describe mismatch repair

Answer 34

old strand has methyl group at GATC sequence --> allows for differentiation mismatch repair (MMR) complex brings the mismatch sequences close to the GATC sequence (forms a loop) and nicks polymerase and ligase fill the gaps mutations in MMR can lead to cancer

Question 35

what is direct repair?

Answer 35

PHOTOLAYSE breaks bonds between thymine dimers caused by UV light O6-methylguanine-DNA methyltransferase removes methyl group from methylated guanine

Question 36

describe base excision repair

Answer 36

DNA glycosylase removes JUST the damaged base creates an apurinic/apyrimidinic (AP) site AP endonuclease cleaves phosphodiester bond deoxyribose sugar removed DNA polymerase fills in the gap and ligase seals gaps

Question 37

describe NUCLEOTIDE excision repair

Answer 37

an enzyme complex recognizes the damage distorting the DNA helix DNA strand is separated, SSBPs stabilize the strand enzymes cleaves mutated strand, helicase removes it gap is sealed by polymerase and ligase

Question 38

describe the mutations caused by DOUBLE STRANDED BREAKS

Answer 38

stalls DNA replication, which could cause chromosomal rearrangements

Question 39

describe HOMOLOGY DEPENDANT repair

Answer 39

homologous chromosomes align NTs enzymatically removed, producing what looks like sticky ends a free 3' invades and displaces a strand of unbroken DNA and elongates displaced strand forms a loop, which pairs with the broken DNA molecule DNA synthesis occurs, strand attachment produces holiday junctions

Question 40

describe NONHOMOLOGOUS END JOINING

Answer 40

often happens during G1 phase more error prone Ku proteins detect the breaks and call polymerase and ligase to fix whatever breaks they can