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adv mol cell > DNA replication > Flashcards

DNA replication Flashcards

1
Q

how are nucleotides joined to DNA sequences

A

nucleophilic attack (transfer of electron forming diester bond) on phosphate of new DNTP = binds new nucleotide and releases 2 phosphates

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2
Q

how does DNA replication take place

A
  1. DNA strands are unwound by DNA helicase
  2. DNA polymerase binds at 3’ ligases strands back together
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3
Q

what are Okazaki fragments

A
  • RNA primers bind to DNA and act as template for DNA polymerase to bind to
  • allow DNA polymerase to bind
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4
Q

where are okazaki fragments found

A
  • lagging strand = 5’→3’
    • needs okazaki fragments
  • leading strand = 3’→5’
    • DNA synthesised continually as DNA P binds to 3’ OH
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5
Q

why does DNA polymerase require primers

A

act as a hook to be able to bind to the lagging strand

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6
Q

function of dna primase

A

produces primers
binds to short RNA sequence and inserts DNA hybrids for DNA polymerase to bind to

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7
Q

what primers are produced on the leading strand

A
  • short RNA primer is synthesised using template and NTPs by DNA Primase
  • once RNA primer is in place, DNA polymerase extends it via 3’
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8
Q

what primers are produced on the lagging strand

A
  1. DNA primase makes RNA primer
  2. primase end dissociates and joins further up strand
  3. DNA polymerase extends RNA primer
  4. ribonuclease H removes RNA primer = leaving gap
  5. DNA polymerase extends across gap
  6. DNA ligase seals nick
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9
Q

diseases associated with replication errors

A
  • mutation in genes encoding DNA helicase → werner syndrome (premmie aging)
  • bloom gene mutation → bloom syndrome
    • LOF in RecQ DNA helicase
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10
Q

what is speed of DNA polymerase dependent on

A

processivity (ability to catalyse consecutive reactions without losing the substrate)

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11
Q

what is a high processivity for an enzyme?

A
  • 1 nuc/sec = non-processive
  • multiple nuc/sec = processive
    average no. nucleotides added each time enzyme binds to template
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12
Q

function of sliding clamp

A

-> increases processivity of dna polymerase
- dependent on ATP
- binds to primer:template junction via clamp loader
- ATP breaks off → clamp loader releases → DNA polymerase binds on

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13
Q

what are single stranded dna binding proteins (SSBs)

A
  • hairpins when DNA coils up = stop polymerase
  • SSBs bind to RNA and prevent hairpins
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14
Q

DNA topoisomerases function

A
  • prevent DNA from being tangled during replication
  • enhance processivity of DNA polymerase
  • DNA topoisomerases relax tension resealing the backbone of parental helix
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15
Q

difference between type I and type II topoisomerases

A
  • type I topoisomerases nick and reseal one of the DNA strands with no ATOP
  • type II topoisomerases nick and reseal both DNA strands with ATP
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16
Q

when do replicator selection and origin activation occur

A
  1. replicator selection occurs in G1 = formation of pre-replicative complex
  2. origin activation occurs in S phase = unwinding of DNA and recruitment of DNA polymerase
17
Q

what are replication origins controlled by

A

high levels of cyclin-dependent kinase (cdk) activity in S phase activates existing pre-RC but prevents formation of new pre-RCs
- G1 = low cdk = pre-c formation and no activation
- S1 = high cdk = no new pre-RC and activation

18
Q

cdk levels in G1

A
  • G1 = low cdk = pre-c formation and no activation
19
Q

cdk levels in S1

A
  • S1 = high cdk = no new pre-RC and activation
20
Q

what enzymes are involved in finishing replication

A
  • DNA polymerase and ligase close all but one gap
  • RNA primer at end of chromosome is removed by RNase H ⇒ gap = 3’ overhang
21
Q

what enzyme forms telomeres

A

telomerase

22
Q

what sequence is added to extend the 3’

A

TTAGGG

23
Q

structure of telomeres

A

ribonucleoprotein with intrinsic RNA component acting as template for telomere repeat sequences to be synthesised in step-wise process using reverse transcriptase = telomerase shuffle

24
Q

what is the telomerase shuffle

A
  • telomerase rna pairs up with existing telomere repeat + 3’ overhang
  • telomerase uses this as template to add 3’ nucleotides on
  • shuffles forward to synth next 3 nucleotides and again to bind to next 3 nucleotides etc

adv mol cell (15 decks)

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