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Cell and Molecular Biology > DNA Replication and Repair > Flashcards

DNA Replication and Repair Flashcards

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1
Q

Outline the 3 main characteristics of DNA

A
  • double helix
  • anti-parallel strands
  • semi-conservative
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2
Q

Outline the structure of nucleotides

A
  • DeoxyRibose sugar
  • phosphate group
  • nitrogenous base
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3
Q

Name the bond between bases

A

H bonds

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4
Q

Name the bond between nucleotides

A

phosphodiester bonds

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5
Q

Name the 3 different models of DNA

A
  • semi-conservative
  • conservative
  • dispersive
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6
Q

Outline the conservative model of DNA

A

1 DNA molecule is newly synthesised and the other one consists entirely of the parent

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7
Q

Outline the dispersive model of DNA

A

each strand of DNA contains a mixture of newly synthesised and old DNA

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8
Q

Outline the semi-conservative model of DNA

A

1 strand consists of newly synthesised DNA and 1 strand consists of the parent strand/original DNA

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9
Q

How was DNA proved to be semi-conservative

A

Meselson-Stahl experiment

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10
Q

What are dNTPs

A
  • substrates for DNA polymerase
  • they are nucleotides that can be added to DNA strands
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11
Q

What is needed to initiate a new DNA chain

A
  • RNA primers
  • each new DNA chain starts with the synthesis of an RNA primer
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12
Q

Explain the role of RNA primers in DNA replication

A
  • RNA primer provides the starting point for DNA polymerase enzymes to begin adding DNA nucleotides
  • DNA synthesis can’t happen w/o it
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13
Q

Why does DNA synthesis happen in a 5’ to 3’ direction?

A
  • DNA polymerase can only add nucleotides in a 5’ to 3’
  • proofreading is hard in a 3’ to 5’
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14
Q

Why do eukaryotic organisms have so many DNA polymerases?

A

each polymerase has specific functions in different aspects of DNA replication, repair, and maintenance

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15
Q

What is The Role of Discriminator Amino Acids in DNA polymerases

A
  • prevent the incorporation of rNTPs during DNA synthesis
  • ensure that only dNTPs are accurately incorporated into the DNA strand.
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16
Q

What are exonuclease

A

enzymes that remove incorrectly paired nucleotides

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17
Q

What is the exonuclease activity and its function

A

a type of proofreading mechanism by DNA polymerase which recognises and removes the incorrect nucleotides

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18
Q

What is the purpose of the sliding clamp

A

it tethers the DNA polymerases to the DNA strand so the DNA polymerase doesn’t fly off

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19
Q

What is the replisome

A

a large complex of proteins that helps ensure the accurate replication of DNA

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20
Q

What is the lagging and leading strand

A

lagging: synthesised in short fragments
leading: synthesised continuously

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21
Q

Why is it important to remove RNA fragments in DNA replication

A

it can cause mutations

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22
Q

What is the function of topoisomerase

A

it relieves the tension that builds up when the DNA unwinds

23
Q

What is the function of helicase

A

unwinds the DNA

24
Q

What is the function of DNA polymerase

A

synthesises new DNA strands

25
Q

What is the function of primase

A

it is a type of RNA polymerase that synthesises complementary short RNA primers

26
Q

What was the function of the single-stranded binding proteins

A

they prevent the reannealing of single-stranded DNA regions and protect them from degradation by nuclease

27
Q

What is the purpose of PCR

A

amplify DNA sequences

28
Q

Outline the process of PCR

A
  1. DNA is heated until it separates into 2 strands
  2. DNA primers bind to target sequence
  3. heat tolerant DNA polymerase binds to primers and copies the strand
29
Q

What are the first 2 steps in DNA replication

A
  1. the formation of a replication machine at the origin of replication (replisome will carry out DNA replication)
  2. helicase unwinds DNA + creates replication bubble
30
Q

What is the difference in the origin of replication between prokaryotes and eukaryotes

A

prokaryotes: one origin of DNA replication
eukaryotes: multiple origins of DNA replication

31
Q

How is DNA replication initiated in bacteria

A
  • specific DNA sequences are recognised by initiator proteins which bind and initiate replication
  • DNA methylation decides when DNA replication should happen
32
Q

Why DNA Replication in Eukaryotes is Slower than in Prokaryotes?

A

Bacteria can divide continuously with DNA replication restarting before division is completed, eukaryotes have to wait until the cell cycle is done before starting replication again

33
Q

What is the end-replication problem

A

the ends of eukaryotic chromosomes contain repetitive sequences that shorten over time because they cannot be fully copied during replication

34
Q

What causes the end-replication problem

A

the ends of chromosomes are not covered by Okazaki fragments on lagging strand, so the RNA primers are not replaced

35
Q

What are the long-term consequences of the end-replication problem

A

Every time DNA replication occurs, chromosome gets shorter –> genome will get shorter each time –> organisms will start to lose genes over time

36
Q

How is the end-replication problem overcome

A

they have telomeres to prevent the loss of genes as chromosomes wear down

37
Q

What are telomerase

A

enzymes that extend the length of telomeres preventing from getting shorter

38
Q

Outline the synthesis of telomeres

A
  1. telomerase carries RNA molecule complemntary to the overhanging lagging strand
  2. RNA bases are added until overhang is long enough
  3. DNA polymerase synthesises the DNA strand for replication
39
Q

is what telomerase doing an example of reverse transcription and if so why?

A
  • Yes
  • converting RNA to DNA
40
Q

Is there a correlation between telomeres and ageing

A
  • yes
  • telomeres shorten w/ age
  • adults lose their telomerase activity
  • stem cells keep their telomerase activity
41
Q

What is the relationship between telomeres and cancer

A

cancer cells have active telomerase activity

42
Q

what are the 2 main ways in which DNA errors happen

A
  • proofreading DNA polymerases make errors
  • mutagens (lUV, chemical) can cause errors
43
Q

What is a well known example of DNA damage

A

cancer which is caused by somatic cell mutations

44
Q

What are the 4 common types of DNA damage

A
  • alkylation
  • depurination
  • deamination
  • UV
45
Q

What is alkylation (DNA damage)

A
  • alkyl groups are added to DNA
  • causes base damage
46
Q

What is depurination (DNA damage)

A
  • purine bases are removed from DNA
  • causes bases to be lost
47
Q

What is deamination (DNA damage)

A
  • amino group (NH2) is removed from base
  • causes base to be converted
48
Q

What are the consequences of UV on DNA

A
  • 2 consecutive bases become linked
49
Q

What is base excision repair

A
  • ensures that mutations are not incorporated into the DNA strand
  • it removes incorrect base and DNA polymerase will fill in the gap w/ correct base
50
Q

What is the function of nucleotide excision repair

A

it detects and corrects damage that distorts the DNA double helix caused by UV or other mutagens

51
Q

What are consequences if DNA breaks

A
  • cell death
  • genome instability –> cancer
  • DNA repair
52
Q

Why are DNA lesions harmful for DNA replication

A
  • cause distortion in DNA double helix
  • it can block DNA polymerase ability to recognise and bind to DNA and eventually block/stall DNA replication
53
Q

How can certain DNA polymerase bypass DNA lesions

A
  • they will bind to the lesion
  • they will synthesise DNA opposite to the lesion
  • DNA replication will start
54
Q

What are the “benefits” to our DNA concerning DNA error

A
  • 95% of DNA doesn’t code for proteins so most mutation will not change the function of the protein
  • each human has 2 copies of one gene

Cell and Molecular Biology (8 decks)

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