Dna Mutation & Repair

Front 1

DNA sites are mostly electrophillic or nusleophilllic?

Back 1

nucleophillic

Front 2

What is the source of most human mutations?

Back 2

sperm cells, because they replicate ca. 40 times before they mature

Front 3

Rare imino form of cytosine structure

- what nu does it bind to?

Back 3

binds to Adenosine instead of Guadosine

Front 4

Rare enol form of thymidine structure

what Nu does it bind to?

Back 4

binds to G instead of A

Front 5

Rare imino form of Adenosine structure

what Nu does it bind to?

Back 5

binds to C instead of T/U

Front 6

Rare enol form of Guanosine structure

what Nu does it bind to?

Back 6

binds to T instead of C

Front 7

Tautomeric shift mutation

- what happens
- how is it repaired?

Back 7

a nucleotide may spontaneously transition to its rare tautomer form, then pair with the incorrect W-C base pair

-

Front 8

transition

transversion

Back 8

transition- purine to purine or pyrimidine to pyrimidine shift

transversion- purine to pyrimidine or pyrimidine to purine shift

Front 9

enolization

Back 9

misspairing of the opposite base

- usual cause of transitions

Front 10

spontaneous deletion

Back 10

at times, DNA is not a strict double helix
polymerase may skip a looped out sequence to make a spontaneous deletion

- may occur when identical sequences occur before and after the loop

Front 11

cause of Huntington disease

Back 11

an increase in the number of glutamine residues in huntingtin protein caused by bulging of triplet nu repeat CAG

Front 12

sources of spontaneous/induced DNA damage (4)

Back 12

1. reactive oxygen species
2. hydrolysis of glycosidic bonds (acid catalyzed)
3. hydrolysis/deamination of C/A
4. light induces formation of thymidine dimers

Front 13

direct damage repair

indirect damage repair

Back 13

direct - lesion reversed

indirect - enzymes cut out lesion

Front 14

example of reactive oxygen species damage

Back 14

8-OxoG

- results in Hoogsteen bp with A

Front 15

example of depurination- hydrolysis of glycosidic bond

Back 15

Front 16

example of spontaneous deamination

Back 16

converts amino groups to keto groups by addition of water and elimination of ammonia

Front 17

thymine dimers

- how is it repaired?

Back 17

formed by reaction of UV light with two T's on same DNA strand

- reversible by enzyme DNA photolyase
or repaired by uvrABC system

Front 18

what atoms in DNA bases are nucleotides?

Back 18

N's & O's

Front 19

example of DNA alkylation

Back 19

O6 and N7 are common alkylation sites; N3 is also reactive

Front 20

Benzopyrene

Back 20

Cyp 450 converts to epoxide which can slip in between bases to bind and remove base -> abasic site

Front 21

Aflotoxin B1

Back 21

a natrual product synthesized by a mold that can be activated in the liver to a potent carcinogen

Front 22

immediate mismatch repair during synthesis

Back 22

edited directly by pol III (3' - 5'' exonuclease activity)

incorrect base pairing slows polymerase enoufh to allow the new DNA strand to enter the exonuclease site for hydrolysis

- this activity increases accuracy of DNA synthesis by over 100-fold

Front 23

MutSLH repair

Back 23

three part enzyme that repairs a mismatch
1. binds to site →activates endonuclease
2. nicks new DNA containing mismatch
3. exonuclease removes segment
4. DNA pol III fills in the gap
5. Ligase connects strands

Front 24

DNA methylation

Back 24

allows identification of newly synthesized strands; repairs must occur before methylation

Dam methylase methylates new DNA strand

Front 25

uvrABC system

Back 25

excision repair of thymidine dimers

1. excision of a 12 Nu fragmant by uvrABC exinuclease
2. DNA synthesis by DNA Pol I
3. joining by ligase

Front 26

excision repair of uracil and alkylated bases

Back 26

1. recognition and hydrolysis by glycosidase
2. nicking DNA next to abasic sugar by endonuclease
3. repair by pol I
4. sealing by DNA ligase

Front 27

methylase

Back 27

methelates a specific site in a DNA strand

- looks for a specific sequence then methelates one nucleotide

Front 28

AlkA

Back 28

removes a mismatched nu to yield an abasic site for repair by pol I and ligase

Front 29

8-oxoG repair

Back 29

three enzymes: MutMYT

1. endonuclease cuts strand
2. exonuclease removes bases
3. ligase fills back in

*** 8-oxoG can be more difficult to detect b/c it looks like a WC base pair***

Front 30

DNA photolyase

Back 30

direct repair of thyamine dimer- by SOME organisms

uses folate and flavin cofactors
needs white light

Front 31

O6-MeGuanine Alkyltransferase

Back 31

direct repair of alkylated guanin in DNA

- accelerates reaction but is not a true enzyme because it cannot turn over. Once the cysteine is alkylated, the enzyme is dead

Front 32

how does Ames test detect

Back 32

a mutated strain that requires a specific medium for growth will proliferate around a disc of that medium placed on an agar plate

- used to detect genotoxic agents

Front 33

homologous recombination

Back 33

the swapping of genetic segments between two DNA duplexes of similar sequence

- increases genetic diversity in sexual reproduction
- can repair severely damaged DNA
- process for deletion, swapping, or integration of foreign DNA segments into bacteria or other hosts

* has been important for initial trials of gene therapy; normal human genes are exchanged for mutated copies in human cells

Front 34

crossover

Back 34

homologous recombination

Front 35

Rec A protein

Back 35

catalyzes strand exchange between homologous DNA molecules

- needs ATP

Front 36

Holliday junction

Back 36

important intermediate of homologous recombination

- the process requires endonuclease to create nicks in phosphodiester backbone and recA enzyme to catalyze strand invasion and progression

Front 37

homologous recombination mechanism

Back 37

1. endonuclease cuts
2. strand exchange
3. ligation
4. branch migration
5. resolution