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Genetics > DNA replication and the cell cycle > Flashcards

DNA replication and the cell cycle Flashcards

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Biology 101 flashcards
1
Q

telomere

A

highly repetitive DNA that allows the end of the chromosome to be replicated- also protects it from degradation

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2
Q

centromeres

A

repetitive dna which forms the spindle attachment site in mitosis

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3
Q

origin of replication

A

special sequence where duplication of DNA begins; each chromosome will have many origins

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4
Q

features of the chromosome that reflects their need to replicate and partition

A

telomere
centromere
origin of replication

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5
Q

DNA pol
vs
RNA pol

A
  • dna polymerase is far more accurate - due to it having a longer lifespan
  • DNA polymerase has a proof reading mechanism- it can detect if it has incorporated the wrong base–> CAN GO BACK AND REMOVE FALSE NUCLEOTIDES AND THIS IS DONE BY EXONUCLEASE
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6
Q

does RNA polymerase have a proof reading mechanism

A

no

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7
Q

evidence of semi conservative dna: Meselson and Stahl

A
  • they proved this by growing bacteria for many generation in DNA that contained a heavy isotope of nitrogen called N15- which became incorporated in the DNA- DNA became more dense
  • they then grew it for a number of generations in normal nitrogen
  • all dna became less dense
  • proved half dna was conserved
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8
Q

what is needed for dna syntehsis

A

DNA polymerase and Mg2+
dNTPs (deoxynucleotides)
single stranded template of DNA
-primers 3” OH group- short single strand of DNA with a hydroxyl group

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9
Q

dna synthesis occurs

A

5’ to 3’ because DNA polymerase acts on the 3’-OH of the existing strand for adding free nucleotides

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10
Q

what provides energy for polymerisation

A

when nucleotide joins the growing DNA polynucleotide- 2 phosphates are lost–> leaving one to join

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11
Q

complementary base pairs are joined via

A

h bonds between single stranded dna

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12
Q

dna polymerase requires

A

a primer with a 3’OH residue to extend from

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13
Q

bacterial genomes are..

A

small, compact, circular

  • no histones
  • associated with Mg2+ and polyamides
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14
Q

eukaryotic genomes

A

large
arranged as a liner chromosomes
histones

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15
Q

what determines the speed of replication

A

sliding clamp- around 50bp per s in eukaryotes. In bacteria around 1000bps

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16
Q

what loads the sliding clamp on the DNA

A

clamp loader

-sliding clamp encircles the double stranded dna and ensures high productivity

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17
Q

enzymes at the replication fork

A 
helicase
ss binding protein
primate
DNA polymerase
sliding clamp
nucleases
dna ligase
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18
Q

helicase

A

unwinds double stranded DNA

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19
Q

ss binding protein

A

stabilises ssDNA

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20
Q

primase

A

synthesises RNA primer

21
Q

dna polymerase

A

synthesis of new dna strand

22
Q

dna polymerase

A

proof read

23
Q

siding clamp

A

keep dna polymerase on DNA

24
Q

nucleases

A

trim the okazaki fragments

25
Q

dna ligase

A

join okazaki fragments

26
Q

okazaki fragments

A

Okazaki fragments are short, newly synthesized DNA fragments that are formed on the lagging template strand during DNA replication. They are complementary to the lagging template strand, together forming short double-stranded DNA sections

27
Q

single stranded binding proteins

A

prevents base-pairing until DNA polymerase arrives- however does mot mask the nucleotide – otherwise single stranded dna may base pair with itself and become folded

28
Q

which protein detects incorrect base pairing in newly synthesises DNA

A

mismatch repair protein MutS- detects incorrect base pairing in newly synthesised DNA

29
Q

mismatch protein mechanisms

A

erro in newly made strand

  • mistmatch proofreading proteins attach-nut s to strand and MutL to the Mut S.
  • dna is scanned and detects nick in new dna
  • this area is removed
  • this area becomes single stranded and the correct nucleotides will join
  • repaired dna
30
Q

DNA synthesis is …

A

bidirectional from sites of origin- there may be a number of sites of origin–> forms replication bubbles

31
Q

what forms replication bubbles

A

the bidirectional nature of dna synthesis

32
Q

s phase

A

dna replication

33
Q

m phase

A

mitosis

34
Q

G1 and G2

A

where checking mechanism occur and events that occur between replication and division

35
Q

where is the site of dna replication

A

replication fork

36
Q

events at replication fork

A
  • both strands copied at replication fork
  • 5’ to 3’
  • leading strand will have continuous synthesis (only needs to be initiated one)
  • lagging strand will have discontinuous synthesis (multiple rounds of initiation and synthesis
37
Q

leading strand

A

continous synthesis- only needs to be initiated once

38
Q

lagging strand

A

discontinue synthesis- multiple rounds f imitation and synthesis

39
Q

however bacterial dna has…

A

one origin of replication

40
Q

what loads histones onto newly synthesised DNA

A

histone chaperons –> to condense the new dna into chromosomes

41
Q

helcase unwinding of dna causes

A

supercoiling ahead of the replication fork which needs to be unwound by TOPOISOMERASE- by breaking and reforming phosphodiester bonds

42
Q

which enzymes undoes supercoiling before the replication fork

A

topoisomerase- breaking and reforming phosphodiester bonds

43
Q

why do leading and algid strand occur

A

due to the antiparallel nature of dna–> synthesis is occurring in the opposite direction on each stand. Lagging strand is more complicated because it is synthesises 3’ to 5’ meaning a diff type of dna polymerase is used

44
Q

why is lagging strand more complicated

A

synthesised from 3’ to 5’- meaning a diff dna polymerase is used

45
Q

what is the lagging strand also referred to

A

OKAZAKI FRAGMENTS

46
Q

synthesis of the lagging strand

A
  1. primase synthesises short RNA oligonucleotides (primers) copied from dna
  2. dna polymerase elongates RNA primers with new dna
  3. nucleases remove RNA at 5’ end of the neighbouring fragment and dna polymerase fills in the gap
  4. dna ligase connects adjacent okazaki fragments
47
Q

how many basepairs per second in bacteria

A

1000bps

48
Q

how many BP per second in eukaryotes

A

50bps

Genetics (24 decks)

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