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MCM Test 4 > B2.060 DNA Replication > Flashcards

B2.060 DNA Replication Flashcards

1
Q

what phase of the cell cycle does DNA replication take place during?

A

S

synthesis

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2
Q

what does semi conservative mean?

A

parental strands are the template for synthesis of new DNA

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3
Q

what direction is DNA synthesized in?

A

nucleotides added to the 3’ end of growing DNA polymer

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4
Q

what are the steps of DNA synthesis

A
  1. Identify origins of replication
  2. Unwind dsDNA
  3. Initiate (primer synthesis)
  4. Elongate (fix over-winding)
  5. ligate newly synthesizes DNAs on lagging strand
  6. terminate replication
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5
Q

what is the function of the origin recognition complex?

A

ORC binds to origin DNA at late M/early G1 phase

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6
Q

what is the function of cdc6 +cdt1 in replication?

A

recruit/load six subunit MCM helicase complex onto origin during late M/ early G1 phase

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7
Q

what happens when cdc6 and cdt1 are release?

A

exit nucleus and are degraded until after mitosis

this makes sure only one replication event occurs per cell cycle (licensing replication)

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8
Q

what are the components of the pre-replicative complex?

A

ORC
cdt1
cdc5
MCM

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9
Q

what occurs in the transition from pre-replicative to replicative complex?

A

CDK phosphorylated MCM, activating helicase
MCM unwinds DNA
ORC leaves
ssDNA coated by replication protein A (RPA)

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10
Q

how are primers synthesized?

A
  1. DNA primare makes a 10-15 nt RNA

2. DNA pol alpha adds 30 nt onto RNA

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11
Q

how many primers are at the beginning of the leading strand?

A

one

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12
Q

how many primers are required on the lagging stand?

A

many for ongoing synthesis

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13
Q

what enzyme synthesizes DNA?

A

DNA pol d/e

PCNA (proliferating cell nuclear antigen) clamos the DNA pol d/e onto the DNA

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14
Q

what are okazaki fragments?

A

new DNA on lagging strand
1000 bp long
each has RNA primer
must be joined together

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15
Q

what is the over winding problem?

A

strand separation at the replication fork causes positive supercoiling of the double helix downstream

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16
Q

what enzyme helps w the over winding problem and how?

A 
topisomerase 1 (DNA gyrase in bacteria)
introduces negative supercoils ahead of fork by creating a single stranded nick which allows DNA to spin
17
Q

describe the process of okazaki fragment maturation

A
  1. DNA pol d/e initiates at primer, elongates DNA to next primer
  2. DNA pol d/e displaces primer and endonuclease cuts off “flap”
  3. DNA pol d/e fills in DNA, leaves single nick
  4. DNA ligase seals the nick w AT{
18
Q

what is a nick?

A

absence of a phosphodiester bond in a DNA backbone

19
Q

what is telomerase and what is its function?

A

reverse transcriptase enzyme

helps lengthen telomeres that tend to shorten w successive replication events

20
Q

what is the Hayflick limit?

A

approx. 50 cell divisions before senescence

due to shortening of chromosomes

21
Q

which types of cells express telomerase?

A 
stem cells
cancer cells (immortality)
22
Q

what are some mechanisms as using DNA replication as a drug target?

A

block/reduce synthesis of nucleotides
inhibit DNA polymerase
cross link DNA strands; no separation
incorporation of DNA analogues into growing chains

23
Q

what types of diseases can be targeted at DNA replication?

A

viral/microbial infections

neoplastic diseases

24
Q

how do drugs like acyclovir /foscarnet select for viruses and not destroy all cells?

A
  1. viral enzyme needed to phosphorylate/activate drug

2. drug blocks viral DNA polymerase specifically

25
Q

what are the 3 checkpoints of cell cycle control?

A

G1-S: integrity of DNA
-R: restriction point (late G1)
G2-M: DNA duplication
M: attachment of kinetochores to spindles

26
Q

what 2 key proteins are involved in cell cycle control?

A

p53- genome integrity/replication

RB-conditions are “pro-division”

27
Q

describe the cyclin-CDK-RB process

A

cyclin proteins are expressed at specific points in the cell cycle
CDKs are activated when bound to cyclins
phosphorylation of RB allows cell cycle to proceed past checkpoints

28
Q

what happens to p53 under normal conditions?

A

p53 degrades during cell cycle

allows for progression past chekpoints

29
Q

what happens to p53 during cell stress/DNA damage?

A

p53 stabilizes, halts cell cycle
cells recover>transverse cell cycle
damage too severe>apoptosis

30
Q

what are the 3 classes of regulators?

A

cyclins
CDKs
CDK inhibitors

31
Q

how are CDK inhibitors controlled?

A

signaling events indicating cell is not ready to divide

p53 increases translation of CDK inhibitors too

32
Q

what phosphorylates cdc6 and cdt1?

A

CDKs

MCM Test 4 (19 decks)

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