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Y1 IMS- Nucleic Acids > 3 DNA Structure And Replication > Flashcards

3 DNA Structure And Replication Flashcards

1
Q

What was Griffith’s experiment - give a summary of the steps and findings

A
  • He used Streptococcus pneumonia = two strains — rough and smooth and injected the two strains into different mice
  • rough strain= killed mice
  • smooth strain = mice lived
  • heat killed smooth strain = mice lived
  • rough strains and heat killed smooth strain = mice died
  • therefore, there suggested there was a transforming agent being transferred
  • we know now the transforming agent was DNA
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2
Q

Which strain of S. pneumonia is virulent (in Griffiths experiment)

A

Smooth strain. ( it has a capsule around it which protects it from our immune system and is therefore virulent)

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3
Q

Which strain of S.pneumonia is nonvirulent

A

Rough strain

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4
Q

What was Avery’s experiment

A

He broke down smooth bacteria into different component and injected each with rough strain
- only DNA from smooth strain caused pneumonia

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5
Q

What did Hershey and Chase find

A

Confirmed the role of DNA - concluded that it has genetic material

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6
Q

Give a summary of Hershey and Chase’s experiment

A
  • had two batches of bacteriophage
  • one batch = sulphur radioactively only labels phage proteins
  • other batch = phosphorous only radioactively labels phage DNA
  • each batch infected different cultures of bacteria
  • cultures filtered, centrifuged
  • only phosphorous found in Pallat, sulphur in supernatant
  • therefore, DNA was injected into bacteria
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7
Q

What were Chargaffs findings

A

found ratio of A:T & C:G was same in each species – but variation between species

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8
Q

What were some of Watson and Cricks findings

A
  • DNA has a double helical structure

- each strand of DNA acts as a template for new strand

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9
Q

What is a nucleotide in DNA made of

A

Deoxyribose sugar
Base
Phosphate

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10
Q

Which bond links the sugar to phosphate molecule

A

Phosphodiester bond

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11
Q

What is the sugar phosphate backbone made of

A

Deoxyribose sugar and phosphate

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12
Q

What is DNA coiled around

A

Histone

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13
Q

Which genes are more loosely coiled - active or silent?

A

Active genes

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14
Q

What is chromatin

A

DNA coiled around histone - efficiently packages DNA to take up less volume

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15
Q

What is Meselson and Stahl’s experiment

A
  • Grew E.coli in a medium containing heavy n15
  • Bacteria took this up and used to to make new DNA
  • this bacteria was added to a n14
  • 1st generation = Hybrid of light and heavy DNA
  • 2nd generation = some hybrid, some only consisted of n14
    — EVIDENCE for semi- conservative replication
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16
Q

Which enzyme unwinds the two strands of the DNA

A

DNA helical

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17
Q

How does DNA helical separate the two strands

A

By breaking hydrogen bonds

18
Q

What do single strand binding proteins do

A

Stabilise the denatured DNA to prevent it from winding back up into a double helix

19
Q

Which enzyme synthesises a shirt RNA primer for the start of replication

A

DNA primase

20
Q

Give a summary of the steps in DNA replication in prokaryotes

A
  • initiates at origin of replication
  • DNA helical unzips the two strands
  • leading strand:
    —Primer binds to end
    — DNA polymerase binds and goes along adding new complementary bases in 5’ to 3’ direction
  • lagging strand:
    — Several RNA primers bind to different points of the strand
    — chunks of DNA are added = Okazaki fragments
  • exonuclease strips away the primers
  • DNA polymerase III fills in the gaps left when primers are removed
  • new strand is proofread
  • DNA lipase seals fragments
  • new DNA winds up into a double helix
21
Q

Role of exonuclease in DNA replication

A

Strips away the primers

22
Q

Why is DNA replication semi-conservative

A

Each new DNA molecule made consists of one new and one old chain strand

23
Q

What is the direction of growth of the leading strand

A

5’ to 3’ (read up write down)

Top strand is always 5’ at the beginning = leading strand

24
Q

Which enzyme is used to seal the gaps between the Okazaki fragments in DNA replication

A

DNA ligase

25
Q

Which strand grows continuously in DNA replication

A

Leading strand

26
Q

Which strand grows in fragments in DNA replication

A

Lagging strand

27
Q

How many dNTPs does DNA synthesis require

A

4

28
Q

Which enzyme catalysed the formation of phosphodiester bonds

A

DNA polymerase

29
Q

What is the phosphodiester bond formed between

A

3’ OH of nucleotide on the primer strand and the phosphate of the incoming dNTP

30
Q

What does the formation of bonds in DNA synthesis release

A

Disphosphate

31
Q

What is the frequency of errors during replication usually

A

1 in 10^5

32
Q

What is the frequency of errors after DNA polymerase carries out 3 to 5’ editing function

A

Reduced to 1 in 10^7

33
Q

What is the error frequency when other enzymes check for mismatched bases after replication

A

1 in 10^9

579

34
Q

What can mutations be a cause of

A
  • spontaneously (replication errors)

- induced by dna damage (eg mutagens)= endo/ exogenous

35
Q

What are the four types of gene mutations

A

Base substitution
Deletion bases
Insertion bases
Rearrangement bases

36
Q

Base excision repair proteins function

A

Cut it damaged bases = different proteins used for different types of damage

37
Q

Nucleotide excision repair proteins function

A

Less specific and cut our larger sections of DNA to remove damage before replication occurs

38
Q

What does deamination of cytosine create

A

Uracil

39
Q

What can happen if cytosine is deaminated into uracil and this is not repaired

A

Mutation

40
Q

Which enzyme recognises uracil in DNA and cuts it out

A

Enzyme Uracil N-glycosylase

Y1 IMS- Nucleic Acids (4 decks)

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