DNA Replication and Repair Flashcards
True or false: the DNA chain grows 5’ to 3’
True
In the messelson stahl experiment what isotopes resulted from conservative, dispersive and semi conservative?
Conservative N14 and n15
Dispersive N14N15
Semi conservative gen 1 N14n15, and gen 2 N14 and N14N15
What phase of cell division does Pre-RC form?
G1
What 3 proteins make up the licensing portion of cell replication?
ORC
MCM
CDC 6
In firing, what helices is used? What are the 3 components?
CMG helicase
CDC 45
MCM
GINS
which two proteins in CMG are phosphorylated and by which kinase?
CDC 45 by DDK
GINS by CDK
Which polymerase is used to add first 20 nucleotides in firing?
DNA polymerase a
True or false: replication bubble is formed during firing by CMG helicase
True
Which polarity number are nucleotides added on to?
3’ end
What are the steps in elongation
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
Explain termination
DNA pol Delta displaces rna primers
Fen 1 clips RNA
DNA ligase seals nicks
What does FACT do during replication?
Helps CMG helices displace histones during replication
What other two proteins associate with FACT?
ASF 1 moves histones 3 and 4 onto CAF 1
CAF 1 associates with PCNA
what does telomerase do?
Is a reverse transcriptase and fills in the gaps at telomeres for replication and prevention of degradation
RNA dependent and DNA polymerase
What do chaperone proteins do
help histones find their new homes
what does ASF1 do?
binds to (picks up) H3-H4 dimers and delivers them to the CAF1 complex
What is CAF1 associated with
PCNA
True or false: histones are only remodeled during DNA replication?
False
Histones are also remodeled when?
For repair, transcription and protein turnover
What is shelterin?
a protein complex that helps to maintain the T-loop position and protect the chromosomes from accidentally being “repaired”
What does PCNA do?
takes the dimers from CAF1 and places the histone dimers back onto the DNA
true or false: do telomerase expression decrease as cells age?
True
True or false: reverse transcriptase = telomerase?
True
DNA polymerases for replication and repair are?
DNA-Dependent DNA polymerase
What is a t-loop
Telomeres contain repetitive sequences, the single stranded DNA end of the chromosomes can invade the upstream telomere sequence making a loop.
What causes Short Telomere syndromes (STSs)
mutation in telomerase (protein, RNA, trafficking, stability)
mutation in shelterin
What is the result of STSs
results in premature aging of cells due to the loss of telomeres
- Premature gray hair
- Osteoporosis
- increased prevalence of cancer
Are organs systems with high turnover vulnerable to STSs
Yes
what organ systems are vulnerable to STSs
Bone marrow-anemias immune system- cytopenias lungs- idiopathic pulmonary fibrosis liver- cryptogenic cirrhosis GI tract- defects in regenerating GI epithelium
Is there any treatment for STSs
not treatable just treat symptoms
True or false: polymerase a, delta and e have an exonuclease domain
true
what does an exonuclease domain do and allow
exonuclease chews from the end and allows for proofreading capabilities
what is the master proofreader
pol delta
what is the worst proofreader
pol alpha
Why does proofreading start?
Proofreading starts by noticing that DNA is the wrong shape
explain the steps of proofreading
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
what does proofreading mean?
BOTH strands of DNA are synthesized in a discontinuous fashion
Replication fidelity vs repair
replication > repair
What causes mutations in changes in hydrogen bonding potential (small distortions in DNA double helix)
unfavored tautomers
modified nitrogenous bases
How can mutations in changes in hydrogen bonding potential be “corrected”
proofreading and base pair excision repair
what causes mutations that result from error- prone repair of structural distortions (Big structural changes)
Depurination
covalent adducts with chemicals or between nitrogenous bases
how can mutations that result in error prone reprise of structural distortions be corrected
translation synthesis and nucleotide excision repair
what is XP
Xeroderma Pigmentosum
what causes XP
caused by mutation in XP gene
XP genes do what?
they are UV repair proteins and part of TFIIH
what results from XP
extreme photosensitivity
severe sunburn
freckles and other sin pigment changes
Is anything damaged due to XP
eyes and skin
skin cancer starts in childhood and vision impairment
Is there any treatment for XP?
no just treating effects
