DNA Mutation and Repair

Question 0

DNA Damage- Chromosomal:

Answer 0

large double stranded breaks, translocations, aneupoloidy (unusual number)

Question 1

Healthy cell: rate of DNA damage= rate of DNA repair

Diseased cell: rate of DNA damager>rate of DNA repair

Answer 1

Duh.

Question 2

DNA damage- intrachromosomal ____ and ______

Answer 2

deletions and duplications

Question 3

DNA damage- Single strand small scale mutations:

Answer 3

small deletions & duplications, point mutations

*** MOST COMMON with point being the most most

Question 4

genetic variations are important for _______ but bad for survival of an individual.

Answer 4

evolution

-individuals require mutations to be repaired

Question 5

Aging can be thought of as….

Answer 5

and accumulation of damage and mutations

Question 6

DNA is structured to be repaired because…

Answer 6

the double helix carries two separate copies of all genes and when one strand is damaged, the the complementary strand can be used to restore the correct nucleotide sequence

Question 7

Environmental factors that cause mutation:

Answer 7

heat, radiation, chemical carcinogens, dietary components, infectious agents, pro-carcinogens that require cell processing

Question 8

Benzo[a]pyrene is an aromatic polycyclic hydrocarbon that is produced by …

Answer 8

cigarette smoke

***carcinogen

Question 9

Benzo[a]pyrene is not a carcinogen until …….

Answer 9

it is oxidized within the cell, then it binds to guanine residues distorting the helix and interrupting G-C base pairing

**causes G–> A transition mutations

Question 10

a common target of activated benzo[a]pyrene is the ______ gene

Answer 10

p53 tumor suppressor gene

Question 11

UV rays from the sun can distort the DNA by….

Answer 11

exciting adjacent pyrimidine/thymine bases, causing them to form covalent dimers

***Thymine Dimers

—> melanomas

Question 12

Describe Single Strand DNA Repair (mistakes in DNA replication and spontaneous damage)

Answer 12

1-damage in one strand detected and mismatch proofreading proteins find it
1.5A- proteins look for nick in one strand to determine which strand was made recently–>which nucleotide is error
1.5B- proteins look for methyl group in one strand to determine which strand was the original template (the one with the methyl)
2-nuclease cuts out DNA surrounding damaged region +damage
3- Repair DNA poly correct nucleotides cut out with complementary strand
4- Ligase fixes Nick

Question 13

A spontaneous change in DNA, called Depurination, involves…

Answer 13

N-glycosyl linkages to deoxyribose for purines (A, G) hydrolyzes/breaks

*** purine leaves strand and the pairing can be deleted if uncorrected

Question 14

Spontaneous change in DNA- Deamination of cytosine is….

Answer 14

the amine group of cytosine removed—-> uracil

** if uncorrected, the complementary G can be changed to A

Question 15

Deamination of 5-methyl Cytosine yields _____ which causes problems because….

Answer 15

Thymine (instead of uracil with just cytosine) because T is an actual DNA nucleotide unlike U, so the error is more likely to be missed

Question 16

Most point mutations occur as a result of mistakes made during ______

But what’s in place to fix it?…

Answer 16

DNA synthesis

***but DNA synthesis does have own repair with the 3’-5’ exonucleolytic proofreading and repair of DNA polymerase

Question 17

Describe BER.

Answer 17

Base Excision Repair:

1. Uracil DNA glycosylase removes deaminated cytosine (uracil) from DNA
2. Sugar-phosphate backbone of missing base cut out by AP endonuclease and phosphodiesterase
3. DNA poly fills in and DNA ligase joins everything together

Question 18

Describe NER

Answer 18

Nucleotide Excision Repair:

1. enzyme recognizes bulky region of *thymine dimer
2. DNA helicase removes area of strand around dimer with dimer
3. DNA poly + ligase fix it all up

Question 19

Xeroderma pigmentosum is an autosomal recessive disease of defective ______ that causes marked sensitivity to UV radiation

Answer 19

DNA repair–> enzymes for NER

Question 20

When both strands of double helix break, there is no intact template for repair; caused by…

Answer 20

ionizing radiation, oxidizing agents, replication errors

*** if not repaired, chromosome degraded in cell

Question 21

The simplest method for repair of ds breaks is…

Answer 21

nonhomologous end-joining: joining the broken ends together by DNA ligation but would also result in some loss of nucleotides

Question 22

The more effective method of repairing ds break is called _______ which:

Answer 22

homologous end-joining: utilizes the other undamaged homologous chromosome and uses general recombination/crossing over mechanism

**more difficult

Question 23

For homologous end joining, the _____ protein play a key role and other accessory proteins are ____ and ____

Answer 23

Rad51 (RecA in procaryotes)

Brac1 and Brac2 –> mutation can cause breast cancer

Question 24

The protein important in non-homologous end joining is _____

Answer 24

Ku protein

Question 25

Damaged DNA signals to block cell-cycle progression at the ____ checkpoint so that the DNA can synthesize repair enzymes

Answer 25

G1

Question 26

An important protein to signal DNA damage is _____

Answer 26

ATM

Automatic Teller Machine

Question 27

______ is an important G1 checkpoint control gene, and is also a favorite for cancer genes to mutate

Answer 27

P53–tumor suppressor gene