DNA Replication and Repair

Question 1

True or false: the DNA chain grows 5’ to 3’

Answer 1

True

Question 2

In the messelson stahl experiment what isotopes resulted from conservative, dispersive and semi conservative?

Answer 2

Conservative N14 and n15
Dispersive N14N15
Semi conservative gen 1 N14n15, and gen 2 N14 and N14N15

Question 3

What phase of cell division does Pre-RC form?

Answer 3

G1

Question 4

What 3 proteins make up the licensing portion of cell replication?

Answer 4

ORC
MCM
CDC 6

Question 5

In firing, what helices is used? What are the 3 components?

Answer 5

CMG helicase
CDC 45
MCM
GINS

Question 6

which two proteins in CMG are phosphorylated and by which kinase?

Answer 6

CDC 45 by DDK

GINS by CDK

Question 7

Which polymerase is used to add first 20 nucleotides in firing?

Answer 7

DNA polymerase a

Question 8

True or false: replication bubble is formed during firing by CMG helicase

Answer 8

True

Question 9

Which polarity number are nucleotides added on to?

Answer 9

3’ end

Question 10

What are the steps in elongation

Answer 10

Helicase unwinds dna 
Primate adds rna primers
Protein C (RPC) clamp loader
PCNA 
Protein A maintains ssDNA
DNA polymerase a adds 20 nucleotides 
DNA pol e does leading strand
DNA pol delta does lagging

Question 11

Explain termination

Answer 11

DNA pol Delta displaces rna primers
Fen 1 clips RNA
DNA ligase seals nicks

Question 12

What does FACT do during replication?

Answer 12

Helps CMG helices displace histones during replication

Question 13

What other two proteins associate with FACT?

Answer 13

ASF 1 moves histones 3 and 4 onto CAF 1

CAF 1 associates with PCNA

Question 14

what does telomerase do?

Answer 14

Is a reverse transcriptase and fills in the gaps at telomeres for replication and prevention of degradation
RNA dependent and DNA polymerase

Question 15

What do chaperone proteins do

Answer 15

help histones find their new homes

Question 16

what does ASF1 do?

Answer 16

binds to (picks up) H3-H4 dimers and delivers them to the CAF1 complex

Question 17

What is CAF1 associated with

Answer 17

PCNA

Question 18

True or false: histones are only remodeled during DNA replication?

Answer 18

False

Question 19

Histones are also remodeled when?

Answer 19

For repair, transcription and protein turnover

Question 20

What is shelterin?

Answer 20

a protein complex that helps to maintain the T-loop position and protect the chromosomes from accidentally being “repaired”

Question 21

What does PCNA do?

Answer 21

takes the dimers from CAF1 and places the histone dimers back onto the DNA

Question 22

true or false: do telomerase expression decrease as cells age?

Answer 22

True

Question 23

True or false: reverse transcriptase = telomerase?

Answer 23

True

Question 24

DNA polymerases for replication and repair are?

Answer 24

DNA-Dependent DNA polymerase

Question 25

What is a t-loop

Answer 25

Telomeres contain repetitive sequences, the single stranded DNA end of the chromosomes can invade the upstream telomere sequence making a loop.

Question 26

What causes Short Telomere syndromes (STSs)

Answer 26

mutation in telomerase (protein, RNA, trafficking, stability) mutation in shelterin

Question 27

What is the result of STSs

Answer 27

results in premature aging of cells due to the loss of telomeres - Premature gray hair - Osteoporosis - increased prevalence of cancer

Question 28

Are organs systems with high turnover vulnerable to STSs

Answer 28

Yes

Question 29

what organ systems are vulnerable to STSs

Answer 29

``` Bone marrow-anemias immune system- cytopenias lungs- idiopathic pulmonary fibrosis liver- cryptogenic cirrhosis GI tract- defects in regenerating GI epithelium ```

Question 30

Is there any treatment for STSs

Answer 30

not treatable just treat symptoms

Question 31

True or false: polymerase a, delta and e have an exonuclease domain

Answer 31

true

Question 32

what does an exonuclease domain do and allow

Answer 32

exonuclease chews from the end and allows for proofreading capabilities

Question 33

what is the master proofreader

Answer 33

pol delta

Question 34

what is the worst proofreader

Answer 34

pol alpha

Question 35

Why does proofreading start?

Answer 35

Proofreading starts by noticing that DNA is the wrong shape

Question 36

explain the steps of proofreading

Answer 36

sense incorrect shape stalls replication fork move offending nucleotide to exonuclease domain cleave phosphodiester bond move growing strand back to polymerase domain and try again

Question 37

what does proofreading mean?

Answer 37

BOTH strands of DNA are synthesized in a discontinuous fashion

Question 38

Replication fidelity vs repair

Answer 38

replication > repair

Question 39

What causes mutations in changes in hydrogen bonding potential (small distortions in DNA double helix)

Answer 39

unfavored tautomers | modified nitrogenous bases

Question 40

How can mutations in changes in hydrogen bonding potential be "corrected"

Answer 40

proofreading and base pair excision repair

Question 41

what causes mutations that result from error- prone repair of structural distortions (Big structural changes)

Answer 41

Depurination | covalent adducts with chemicals or between nitrogenous bases

Question 42

how can mutations that result in error prone reprise of structural distortions be corrected

Answer 42

translation synthesis and nucleotide excision repair

Question 43

what is XP

Answer 43

Xeroderma Pigmentosum

Question 44

what causes XP

Answer 44

caused by mutation in XP gene

Question 45

XP genes do what?

Answer 45

they are UV repair proteins and part of TFIIH

Question 46

what results from XP

Answer 46

extreme photosensitivity severe sunburn freckles and other sin pigment changes

Question 47

Is anything damaged due to XP

Answer 47

eyes and skin | skin cancer starts in childhood and vision impairment

Question 48

Is there any treatment for XP?

Answer 48

no just treating effects