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PHA111 > DNA replication > Flashcards

DNA replication Flashcards

1
Q

Describe the Hershey and Chase (1952) experiments proving DNA is the genetic material

A

Viruses were grown in 1 of 2 isotopic mediums to radioactively label a specific viral component.

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2
Q

Describe what happened in the 2 isotopic mediums (Hershey & Chase)

A 
2 mediums: 
1) grown in 35 S
  radio-labelled proteins
   no radioactivity enters cell
   S is present in proteins and not in DNA

2) grown in 12 P
radio-labelled DNA
radioactivity enters cell
P is present in DNA and not in proteins

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3
Q

Once the viruses had infected the bacterium (E.coli), how were they separated?
(Hershey & Chase)

A

Via centrifugation - larger bacteria formed a solid pellet, while the viruses remained in the supernatant

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4
Q

What did Hershey and Chase find was the genetic material of a bacterium?

A

DNA was the genetic material because DNA was transferred to the bacteria

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5
Q

List the 3 methods of replication

A
  • Semiconservative
  • Conservative
  • Dispersive
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6
Q

Describe the semiconservative method of replication

A

2 identical copies of DNA produced - 1 old and 1 new strand

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7
Q

Describe the conservative method of replication

A

2 duplexes containing 2 old strands and the other containing 2 new strands

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8
Q

Describe the dispersive method of replication

A

2 duplexes containing strands of a mixture of old and new

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9
Q

What method of DNA replication did Meselson & Stahl aim to prove?

A

Semiconservative

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10
Q

Describe the method and findings of Meselson & Stahl’s experiment

A
  • bacteria grown in 15 N medium and 14 N medium
  • Samples taken at 0, 20 and 40 mins
  • A centrifuge was used to separate DNA labelled with isotopes of different densities
  • They found a pattern supporting the semi conservative method
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11
Q

Replication is initiated at an ____ of replication that gives 2 replication ____

A

origin

forks

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12
Q

Do prokaryotes or eukaryotes have a larger genome?

A

eukaryote - it has multiple forks

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13
Q

Where is the replication fork and what occurs there?

A

The branch point in the replication eye at which DNA synthesis occurs

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14
Q

Replication forks are almost always unidirectional/bidirectional

A

bidirectional

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15
Q

Rerji Okazaki elucidated the ____-________ method of replication

A

semi-discontinuous

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16
Q

There are 3/4/5 copies of a 9bp sequence that bind ____ proteins

A

4

DnaA

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17
Q

What is the process called when all binding sites are occupied and recruit more DnaA proteins?

A

DnaA barrel formation

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18
Q

What happens after DnaA barrel formation?

A

An A-T rich area of DNA is exposed via torsional stress

19
Q

DnaB initiates the formation of the pre-______ complex

A

priming

20
Q

DnaB/DnaA helicase breaks ___ bonds between base pairs

A

DnaB

Hydrogen

21
Q

Which proteins stop the strands base pairing and protect DNA from attack by free radicals + nuclease enzymes?

A

SSBs - single stranded binding proteins

22
Q

Elongation in prokaryotes:
DnaG (primase) binds near helicase and synthesises the ___ primer on the ______ strand.
SSBs stabilise the _______ strand
DNA ______ III holoenzyme clamps to the ________ strand and synthesises DNA

A 
RNA
leading
lagging
polymerase
leading
23
Q

What enzyme carries out DNA synthesis?

A

DNA polymerase - 5’-3’

24
Q

The lagging strand is generated by the synthesis of ______ fragments, in the same/opposite direction to the movement of the replication fork

A

Okazaki

opposite

25
Q

DNA polymerisation is carried out by which enzyme?

A

DNA polymerase

26
Q

Why does DNA polymerisation occur in the 3’-5’ direction?

A

most favourable energetics

27
Q

What are Okazaki fragments?

A

Short sequences of DNA nucleotides, synthesized discontinuously (3’-5’) and linked together by the DNA ligase to create the lagging strand during DNA replication.

28
Q

In Okazaki fragments which strand is replicated continuously in the 5’ - 3’ direction?

A

leading

29
Q

Parallel replicated DNA is called a _____

A

replisome

30
Q

Why is the helix opened before the head of the fork?

A

To stop over-winding

31
Q

What enzymes alleviate the topological problem of DNA replication?

A

Topoisomerases

32
Q

Describe the action of Type I topoisomerase

A

Introduces a break in one strand to pass the other strand through then seals the break

33
Q

Describe the action of Type II topoisomerase

A

Breaks both strands and passes a double helix through the gap before resealing the break

34
Q

The breaks in DNA are _____ attached to enzymes so they don’t lose the ends

A

covalently

35
Q

In prokaryotes, the two replicons must meet ___ degrees away from the origin of replication

A

180

36
Q

Describe how the regulatory mechanism works in the termination of replication

A

It ensures the replicon meets at a specific point if one gets there first it will wait for the other to arrive before signalling replication completion

37
Q

If the replicon meets a transcription _____ then it will wait and not overtake

A

bubble

38
Q

Once the 2 daughter cells are generated they are _____, and unlinked by __________

A

catenated

topoisomerases

39
Q

Eukaryote replication forks are faster/slower than prokaryotes

A

slower

40
Q

Eukaryote replication forks move at ___ bp/s

A

50

41
Q

What is required to initiate DNA replication in eukaryotes?

A

protein licensing factor complex

42
Q

Why can telomeres not be replicated semi-discontinuously?

A

There is no DNA to elongate once the RNA primer is removed from the 5’ end of the lagging strand - potential loss of genetic material

43
Q

What is the non-coding repeat sequences in chromosomes?

A

TTAGGG - 3’ end overhangs 5’ end

44
Q

What can repressing telomerase activity in somatic cells lead to?

A
  • gradual loss of DNA
  • shortening of chromosomes
  • aging

PHA111 (23 decks)

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