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Biomed > BB1720 DNA: replication and recombination > Flashcards

BB1720 DNA: replication and recombination Flashcards

1
Q

What is DNA replication?

A
  • copying of DNA
  • occurs during mitosis and meiosis, S phase
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2
Q

importance of DNA replication

A

DNA is constantly being damaged
damage must be repaired
replication must be accurate

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3
Q

how is accuracy achieved?

A

complementary base pairing

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4
Q

process of dna replication

A
  • two DNA strands are separated
  • each strand is used to make a - new copy of the missing strand
  • semi conservative
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5
Q

key components of DNA replication

A

dNTPs
DNA helicase
single stranded DNA binding proteins
DNA polymerase

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6
Q

what are dNTPs?

A
  • building blocks of DNA
  • purines -> adenine + guanine
  • pyrimidines -> cytosine + uracil + thymine
  • A and T
  • G and C
  • placed into PCR
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7
Q

What is DNA helicase?

A
  • enzyme that unwinds and separates double helix DNA, antiparallel
  • allows DNA polymerase to gain access and make a copy
  • requires energy
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8
Q

single stranded DNA binding proteins

A
  • binds to single stranded, lagging DNA
  • occurs after helicase unwinds the double helix
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9
Q

function of single stranded DNA binding proteins

A
  • stops strands from being repaired or destroyed
  • prevent base pairing
  • prevent DNA from sticking to itself and block copying
  • prevent formation of hairpins
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10
Q

function of hairpins

A

stops polymerase from working

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11
Q

DNA polymerase

A
  • makes the copy
  • adds dNTPs to 3’ end of the DNA molecule
  • chain grows from 5’ to 3’
  • DNA is antiparallel
  • adds 500-1,000 bases per second and helicase unwinds at the same rate
  • makes mistakes
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12
Q

how does the antiparallel relate to DNA polymerase and replication?

A
  • one strand faces the wrong way for replication
  • the replication fork constantly exposes new bases
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13
Q

how does DNA polymerase use thereplication fork to create DNA?

A
  • bottom strand of the fork has a constant supply of bases to pair
  • top strand runs out of DNA - lagging strand
  • 3’ 5’ ends come back into helicase. 5’ ends come out of the top. 3’ come out the bottom
  • short fragment of DNA produced
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14
Q

why are single stranded binding proteins required for DNA polymerase replication fork mechanism?

A

prevent base pairing and DNA primase
add RNA as start point for DNA polymerase

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15
Q

conditions for DNA polymerase to make copy of DNA

A
  • cant make copy until it has the template
  • needs 3’ OH group to attach nucleoside triphosphate
  • needs a primer - insert U instead of T which is later corrected
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16
Q

what happens when DNA polymerase makes mistakes

A

proof reading
replication stops until error is corrected
if error isnt corrected it’s repaired later

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17
Q

role of DNA topoisomerase

A
  • helps unwinding
  • solves DNA winding problem and supercoiling
  • makes small single stranded break to allow DNA to spin around at the bond
  • creates problem due to break in backbone - repairs DNA phosphodiesterase bone
18
Q

DNA primase

A

builds short RNA primer on DNA template
provide 3’ OH group for DNA polymerase to add the nucleoside triphosphate
inserts u instead of t - corrected

19
Q

DNA ligase

A

join DNA strands together
repairs DNA single strand nick

20
Q

What is DNA recombination?

A

exchange of DNA strands to produce new nucleotide sequence arrangements

21
Q

what is the purpose of DNA recombination?

A

maintain genome integrity
generates genetic diversity

22
Q

how does DNA recombination occur

A

between regions of similar sequences by breaking and rejoining DNA segments

23
Q

what happens during DNA recombination

A
  • homologous chromosomes are nicked at identical locations
  • strands from one side of nick invades chromosomes and base pairing occurs
  • crossing over between two pieces of homologous DNA (4 strands) known as heteroduplex region
  • base pair interactions
  • occur either vertically or horizontally
24
Q

what is the heteroduplex region

A

D E F no longer match to D’ E’ F’
repaired by mismatch repair
formed at the cross over
variety

25
Q

how is the heteroduplex region repaired

A

gene conversion
depends on which strand is used as the template for repair

26
Q

what’s the difference between horizontal and vertical cleavage

A

horizontal does not produce recombinants

27
Q

process of recombination stage 1

A
  • enzymes generate double-stranded break and single-stranded ends on paired homologous chromosomes
  • this allows one DNA strand to invade other strands to match up
  • separation of DNA in one strand runs along the sequence
  • single strands find homologous DNA by DNA synapsis
28
Q

stage 2 of dna recombination process

A

produces different outcomes
- release of invading strand
- capture of the second strand

29
Q

what is the release of invading strand in dna recombination

A

additional DNA synthesis
ligation occurs
no cross over

30
Q

what is the capture of second strand in dna recombination

A
  • synthesis of heteroduplex region - branch migration
  • Additional DNA synthesis occurs
  • formation of cross arrangement where DNA crosses over between two strands, known as Holliday junction
31
Q

what happens in the holliday junction

A
  • an open form of cross occurs if the junction is rotated
  • branch migration
  • cross can be cut horizontally or vertically to separate chromosomes
32
Q

what is branch migration

A

bases pair up
dna strands are swapped between chromosomes
which creates heteroduplex regions
minor base sequence differences result in region of DNA with low percentage of mismatch basepairs

33
Q

what happens when the holliday region is cut horizontally?

A
  • ligation occurs at joint adjacent ends
  • after they join, strands straighten back out
  • small region of variation
  • no recombinant
34
Q

what happens when the holliday region is cut vertically?

A
  • ligation occurs at joint adjacent vertical ends
  • strands straighten
  • all strands crossed over
  • recombination
35
Q

how is RecA protein involved in recombination?

A

enables DNA single strand to pair with a homologous region of DNA double helix

36
Q

when does recombination occur

A

meiosis
homologous recombination repair

37
Q

features of recombination in meiosis

A

swapping over of chromosomes
4 haploid germ cells arent identical
unique due to cross over
hot spots occur - hybrid of genes

38
Q

models of recombination

A

meselson radding
double strand break

39
Q

features of the meselson radding model

A
  • one strand cut
  • DNA synthesis
  • hanging strand displaces a strand from homologous duplex
  • removal of displaced
  • ligation
  • holliday junction
40
Q

features of double strand break

A
  • loss of material from both strands
  • two free sections of DNA
  • two holliday junctions

Biomed (57 decks)

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