DNA replication, enzymes at replication fork & DNA replication accuracy Flashcards

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1
Q

What is a chromosome?

A

nuclear genetic material distributed along chromsomes

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2
Q

What are telomeres?

A

areas of highly repetitive DNA
protect chromosome ends from degradation, recombination & end fusion

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3
Q

what is a centromere?

A

repetitive DNA
forms spindle attachment in mitosis

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4
Q

What is the origin of replication?

A

sequence where duplication of DNA begins
has many

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5
Q

what is semi-conservative replication?

A

discovered by Mehselton & Stahl
centrifugation with different isotopes of N and bacteria
each generation had half light and half heavy N
settle at different points in the test tube

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6
Q

What is involved in DNA synthesis?

A

DNA polymerase
Mg2+
Single stranded template of DNA
Primer 3’-OH
Synthesis in 3’ to 5’ direction

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7
Q

differences between eukaryotic and bacterial genomes

A

euk are large & arranged as linear chromosome
bact are small, compact and circular

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8
Q

what is the replication fork?

A

the site here both strands of DNA are copied at
in 5’ to 3’ direction

leading strand is continuous
lagging strand is discontinuous

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9
Q

what are the discontinuous fragments called?

A

Okazaki fragments

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10
Q

What are the steps in lagging strand synthesis?

A
  1. Primase synthesises RNA primer
  2. DNA polymerases elongate primer with new DNA
  3. Nucleases removed RNA at 5’ end of neighbouring fragment
  4. DNA polymerase fills the gap
  5. DNA ligase connects adjacent Okazaki fragments
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11
Q

What are the different enzymes present at the replication fork?

A

helicase - unwinds DNA
ss-binding protein - stabilises DNA
primase (RNA polymerase) - synthesises RNA primer
DNA polymerase- creates new DNA strand & proof read
Sliding clamp - keeps DNA polymerase on DNA
clamp loader - loads clamp onto DNA
nuclease - trim Okz fragments
DNA ligase - joints Okz fragments

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12
Q

What is primase?

A

specialised RNA polymerase that creates RNA primers

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13
Q

what is the speed of DNA replication?

A

50 base pairs s-1 at each fork
high as DNA polymerase attaches to sliding clamp

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14
Q

What is a sliding clamp?

A

keeps DNA polymerase on the DNA
loaded on by DNA clamp loader

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15
Q

What are the steps of clamp loading?

A
  1. Loader binds to clamp
  2. Opens the clamp
  3. DNA then engages in clamp
  4. ATP hydrolysis locks the clamp round the DNA by closing it
  5. Release of clamp loader
  6. DNA polymerase then binds to sliding clamp
  7. Clamp loader can then be used again
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16
Q

What do single stranded binding proteins do on the lagging strand?

A

prevent an y base pairing within the single strand until DNA polymerase has arrived

17
Q

what is a histone chaperone?

A

load histones onto newly synthesised DNA

18
Q

What is a topoisomerase?

A

untwist DNA by breaking and reforming phosphodiester bonds
preventing supercoiling by DNA helicase
unswivels the DNA before replication fork

19
Q

DNA polymerase accuracy

A

more accurate than RNA polymerase
5’ to 3’ polymerisation 1 in 10^5 errors per nucleotide

MutS detects incorrect base pairing in newly synthesised DNA