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Flashcards in Final: DNA Repair Systems Deck (21)
1

3 basic mechanisms of lesion repair

direct base repair

nucleotide excision repair

base excision repair

2

how to the 3 basic mechanisms of lesion repair work in general?

use proteins to perform corrective chemistry on defective DNA (heal)

3

what are the 1st and 2nd lines of defense against aging and cancer?

1st: antioxidants

2nd: DNA repair

4

4 types of direct repair and # of steps

repair lesions in a single step

alkyl transferase

photoreactivation

nick repair

gap repair

5

alkyl transferases

enzymes pick off alkyl (methyl/ethyl) groups from DNA bases

MGMT methylguanine methyl transferase (1 molecule per methyl..can't reuse)

6

photoreactivation

in bacteria, thymine dimer repaired by breaking it into two thymines again

uses a photon of blue light

7

nick repair

ligase (same enzyme used in last step of DNA replication)

8

gap repair

DNA polymerase fills the gap, then ligase

9

what is excision repair?

cut out a piece of damaged ssDNA

leaves a gap, which is fixed by gap repair

10

Xeroderma pigmentosum

genetic disease caused by defective dimer excision repair system

thymine dimers caused by short-wave UV light (sun)

leads to skin cancer

11

AP site repair system

turn AP site into a gap (nick above missing base)

then gap repair fixes

12

glycosylase repair system

recognize bad bases and cut it out by cutting bond between base and sugar (glycosyl bond)

this cutting leaves an AP site, AP site repair fixes

13

transcription-coupled repair (TCR)

brings an excision repair system to a damaged site during transcription

14

Cockayne Syndrome

genetic disease caused by defective TCR

cells get stalled when transcribing genes (leads to apoptosis)

causes stunted growth

15

symptoms of Cockayne Syndrome

shortness, skeletal deformation, premature aging, MR

16

post-replication repair

fixes some lesions after DNA has been replicated

17

mismatch repair (MMR)

type of post-replication repair

replication error puts wrong base on new daughter strand

identifies parent strand by finding which has methylated adenines

changes incorrect bases on daughter strand to match parent strand

18

2 types of double-strand break repair (DSBR) & why needed?

homologus repair (HR)

non-homologus end joining (NHEJ)

when a double strand break occurs, a small bit of chromosome is lost

19

homologus repair (HR)

repair break in chromosome by lining up broken piece with matching chromatid of DNA (or chromosome)

restores missing sequence and prevents translocation/inversion

20

non-homologus end joining

used when HR fails

stick two broken ends back together

could be the wrong ends, causing translocation/inversion

doesn't replace missing info accurately leadings to deletions/insertions

21

loss of heterozygosity (HR)

if HR uses the homologus chromosome, not chromatid then LOH could occur

other chromosome may have different alleles, making repaired chromosome have recessive alleles