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Mol Med > Unit 2 - Cell Cycle & DNA Repair > Flashcards

Unit 2 - Cell Cycle & DNA Repair Flashcards

1
Q

What do DNA Polymerases require for activity?

A

3’-OH group so need a primer they can extend (5’->3’)

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2
Q

What is the overview of DNA replication?

A
  • DNA unwound +RNA primer molecules bound are synthesized by Primase
  • primers extended by replication polymerases (δ or ε)in 5’->3’
  • lagging strand is discontinuously synthesized
  • also leads to ‘end replication problem’
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3
Q

What solves the ‘end replication problem’?

A

Telomerase (ensures intact replication of DNA ends) (needed because of primer)

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4
Q

What are the steps in DNA synthesis (lagging strand)?

A
  • Helicase unwinds DNA, RPA loads
  • Pol α-primase synthesizes a short primer
  • Pol α displaced + Pol ε or δ loaded
  • Pol ε or δ extend the primer
  • downstream primer is removed (nuclease)
  • okazaki fragments are ligated = continuous strand of new DNA
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5
Q

What happens during Prophase of Mitosis?

A

Chr. Condense

Centrosomes separate

Histones modified

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6
Q

What happens during Prometaphase of Mitosis?

A

Microtubles + chr’s kinetochores

Nuclear envelope breakdown

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7
Q

What happens during Metaphase of Mitosis?

A

Chrs align @ metaphase plate

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8
Q

What happens during Anaphase of Mitosis?

A

Chromatin separate & move -> opp. Spindle poles

Nuclear envelope reassembly

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9
Q

What happens during Telophase of Mitosis?

A

Nuclear envelope reassembles

Poleward movement

Cleavage plane

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10
Q

What happens during Cytokinesis of Mitosis?

A

Separation

Clevage furrow 2/ actin filaments ring

Chrs. Decondense

Nuclear structures reform

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11
Q

What are the key regulatory steps of the cell cycle?

A

Making sure DNA replicates completely + only once (S Phase control)

Making sure that DNA is intact before mitosis begins (G2 phase delays)

Making sure all chrs. Are segregated equally (spindle checkpt.)

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12
Q

What is involved during S Phase control?

A

Prereplicative complex + origins of replication (licensing) during late M/G1

Licensed origins of replication are bound by initiator proteins

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13
Q

What detects DNA lesions in G2 Phase control?

A

Checkpt. Kinase proteins (ATR, ATM) =signal -> effector kinases (ChK1, ChK2)

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14
Q

What does the centrosomes Pericentriolar Material contain?

A

γ-tubulin ring complex that nucleates microtubles

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15
Q

How are centrosomes duplicated? The

A

G1 = disorientation of centrioles

S= procentriole formation

G2= elongation & maturation

M= separation & activation

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16
Q

What separates the spindle poles?

A

Interpolar microtuble motors

not attached to centrosomes

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17
Q

What helps establish the overall cytoskeleton structure?

A

Astral microtubles

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18
Q

What is required for satisfaction of the Spindle Assembly Checkpt.?

A

Both occupancy of kinetochores by microtubles & inter-kinetochore tension

=>anaphase

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19
Q

What are the key regulators of the cell cycle?

A

Cyclin dependent kinases (CDKs)

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20
Q

What are CDKs controlled by?

A

Cyclin levels

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21
Q

What determines the directionality of cell cycle?

A

Transcriptional regulators

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22
Q

How do cycling & CDKs combine?

A

G1/S cyclin

  • CDK4, CDK6 => cyclin D1, 2, 3
  • CDK2 => cyclin E

S cyclin

  • CDK1 => cyclin A
  • CDK2 => cyclin E & A

M cyclin
-CDK1 => cyclin B

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23
Q

What are the key target sites in regulated activation of CDK1?

A

Phosphorylation sites

  • inhibitory sites = T14 Y15
  • activating sites= T161
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24
Q

What will the inhibit activity of CDK1?

A

Wee1/Myt1 phosphorylate inhibitory sites T14 Y15

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25
Q

What will activate activity of CDK1?

A

Cdc25 dephosphorylates activating site T161

CAK phosphorylates activating site T161

26
Q

What are the targets in cell cycle in cancer therapy?

A

M= Antimitotics (target microtubles- vincristine, vinblastine, taxol)

G1->S= Antimetabolites (block nucleic acid synthesis)

S & G2 = (DNA damage) alkylating agents/Pt drugs (radiotherapy type II inhibition)

27
Q

What mutation which changes gene fnx. Is found in 20% of tumors?

A

Activating pt. Mutation in RAS

=prevents hydrolysis of GTP on RAS = RAS accumulates in GTP bound active form

28
Q

How is Base Damage repaired?

A

Base excision repair

29
Q

How is incorporation of mismatched base repaired?

A

Mismatch repair

30
Q

How is the formation of UV photoproduct: 6-4 thymidine dimmer repaired?

A

Nucleotide excision repair

31
Q

How is DSB repaired?

A

Homologous recombo repair

Non-homologous end joining

32
Q

What are the causes of DNA damage that can be repaired by base excision?

A

Gen. Of abasic sites through hydrolytic clevage

Deamination

Ox. Damage

Alkylation damage

33
Q

What recognizes & removes the damaged base in BER?

A

DNA glycosylase

=abasic site

34
Q

What cleaves the DNA @ the AP site in BER?

A

AP endonuclease

35
Q

What carries out repair synthesis in BER?

A

DNA polymerase

36
Q

What rejoins the sugar-phosphate backbone in BER?

A

DNA ligase

37
Q

What recognizes DNA distortion from damaged bases in NER?

A

Complex containing XPA & XPC

38
Q

What can the stalled RNA polymerase act as in transcribed DNA?

A

Recognition signal

39
Q

What unwinds the DNA helix in NER?

A

XPB/XPD

40
Q

What nicks the DNA 5’ & 3’ of the lesion in NER?

A

XPF/Erccl

& XPG removes it

41
Q

What synthesizes the excised sequence in NER?

A

DNA polymerase δ or ε

42
Q

What seals the nicks in NER?

A

DNA ligase

=restoration of integrity of DNA sequence

43
Q

What is required to correct these DNA copying errors?

A

Mismatch repair (MMR)

44
Q

What detects the error in MMR?

A

Mismatch recognition proteins (MSH2/MSH6)

45
Q

What happens to the DNA until the mismatch in MMR?

A

Exonucleotically degraded (remove a lot of sequence & mismatch)

46
Q

What performs the repair synthesis in MMR?

A

DNA polymerase δ or ε

47
Q

What seals the nicks in MMR?

A

DNA ligase

48
Q

What does defective MMR cause?

A

Micro satellite instability

49
Q

What is an eg. of defective MMR’s link to cancer?

A

Hereditary non-polyposis colon cancer (mutation in MSH2 & MLH1)

50
Q

What is the telomere?

A

Special protective nucleoprotein complex @ the ends of linear chrs. to ensure that they are not treated as broken ends

51
Q

What does the rapid repair of SSB in DNA require?

A

poly (ADP-ribose) polymerase (PARP)

52
Q

What initiates repair by non-homologous end joining?

A

Breaks bond by Ku70/Ku80 dimer = recruit kinase = activate repair

53
Q

What religates the broken ends in non-homologous end joining?

A

DNA ligase IV

or

XRCC4

54
Q

When is non-homologous end joining repair of DSB critical?

A

In V(D)J recombo during immune system dev.

55
Q

What initiates homologous recombo repair of DBS?

A

Resection @ break to expose a tract of ssDNA

56
Q

What carries out a homology search in homologous recombo repair?

A

Rad51 recombinase forms a nucleoprotein filament on ssDNA =searches

57
Q

What allows templates DNA synthesis in homologous recombo repair occur?

A

Strand invasion

=holliday jnx.

58
Q

What happens to the resulting Holliday jnx. In homologous recombo repair?

A

Cleaved to = repaired sequence

59
Q

What is a key component of homologous recombo repair?

A

BRCA2 (modulates Rad51)

60
Q

What repairs spontaneous breaks that occur during normal DNA replication?

A

Homologous repair & Parp I- dependent ssb repair

61
Q

What repairs do BRCA2-defective cells use?

A

Rely only on Parp I

Mol Med (3 decks)

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