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IB Biology > 7.1 DNA structure and replication > Flashcards

7.1 DNA structure and replication Flashcards

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1
Q

What did Hershey and Chase try to prove?

A

That DNA was the genetic material

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2
Q

What did Hershey and Chase do to the viruses?

A

They were grown in one of two isotopic mediums in order to radioactively label a specific viral component

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3
Q

What did viruses grown in radioactive sulfur have?

A

Radiolabelled proteins

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4
Q

Where is sulfur present?

A

In proteins but not DNA

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5
Q

What did viruses grown in phosphorus have?

A

Radiolabelled DNA

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6
Q

Where is phosphorus present?

A

In DNA but not proteins

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7
Q

Once labelled, what were the viruses allowed to do?

A

Infect a bacterium

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8
Q

What happened once the viruses infected a bacterium?

A

The virus and bacteria were separated via centrifugation

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9
Q

In hershey and chase, what did the larger bacteria form?

A

A solid pellet

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10
Q

When were the bacterial pellet found to be radioactive?

A

When infected with the radioactive phosphorus

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11
Q

When were the bacterial pellet not found to be radioactive?

A

When infected with the radioactive sulfur

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12
Q

What did the Hershey and Chase experiment demonstrate and how?

A

That DNA, not protein, was the genetic material because DNA was transferred to the bacteria

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13
Q

In hershey and chase, how did the smaller viruses remain?

A

In the supernatant

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14
Q

How did rosalind franklin investigate the structure of DNA?

A

Using a method of X-ray diffraction

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15
Q

What inferences could be made about DNAs structure from the scattering pattern?

A

-Dna is a double stranded molecule
-Nitrogenous bases are packed together on the inside and phosphates form a backbone
- The DNA molecule twists at regular intervals to form a helix

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16
Q

What forms the outer backbone of DNA?

A

Phosphates and sugars

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17
Q

What are packaged within the interior of DNA?

A

Nitrogenous bases

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18
Q

What is DNA composed of an equal number of?

A

Purines and pyrimidines

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19
Q

What are purines?

A

A and G

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20
Q

What are pyrimidines?

A

C and T

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21
Q

In order fo pairing between purines and pyrimidines to occur what must happen?

A

The two strands must run in antiparallel directions

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22
Q

How many hydrogen bonds are between adenine and thymine?

A

Two

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23
Q

How many hydrogen bonds are between guanine and cytosine?

A

Three

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24
Q

What two mechanisms does DNA structure suggest for DNA replication?

A

Replication occurs via complementary base pairing
Replication is bi-directional due to the antiparallel nature of the strands

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25
Q

What is DNA replication?

A

A semi-conservative process that is carried out by a complex system of enzymes

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26
Q

What seven enzymes are used in DNA replication?

A

Helicase
DNA gyrase
SSB proteins
DNA primase
DNA polymerase I
DNA polymerase III
DNA ligase

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27
Q

What does helicase do?

A

Unwinds and separates the double stranded DNA

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28
Q

How does helicase unwind and separate the DNA?

A

By breaking the hydrogen bonds between base pairs

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29
Q

Where does helicase do its job?

A

At specific regions

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30
Q

What does helicase end up creating?

A

A replication fork of two strands running in antiparallel directions

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31
Q

What does DNA gyrase do?

A

Reduces the torsional strain created by the unwinding of DNA by helicase

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32
Q

How does DNA gyrase reduce torsional strain?

A

By relaxing positive supercoils via negative supercoiling that would otherwise form during the unwinding of DNA

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33
Q

What does SSB stand for?

A

Single stranded binding proteins

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34
Q

What does SSB proteins bind to?

A

The DNA strands after they have been separated

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35
Q

What two things do SSB proteins prevent?

A

The strands from re-annealing and the single stranded DNA from being digested by nucleases

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36
Q

What happens to SSB proteins once they’ve done their job?

A

They will be dislodged from the strand

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37
Q

When will SSB proteins be dislodged from the strand?

A

When a new complementary strand is synthesised by DNA polymerase III

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38
Q

What does DNA primase do?

A

Generates a short RNA primer on each of the template strands

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39
Q

What does the RNA primer provide?

A

An initiation point for DNA polymerase III

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40
Q

What can DNA polymerase III do to a nucleotide chain?

A

Extend but not start one

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41
Q

Where do free nucleotides align?

A

Opposite their complementary base partners

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42
Q

Where does DNA pol III attach?

A

To the 3’ end of the primer

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43
Q

What does DNA pol III do?

A

Covalently joins the free nucleotides together in a 5’ - 3’ direction

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44
Q

Which way does DNA pol III move on the leading strand?

A

Towards the replication fork

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45
Q

Which way does DNA pol III move on the lagging strand?

A

Moving away from the replication fork

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46
Q

How does DNA pol III synthesize on the leading strand?

A

Continuously

47
Q

How does DNA pol III synthesize on the lagging strand?

A

In pieces (okazaki fragments)

48
Q

Due to the fact the lagging strand is synthesised in a series of short fragments what does it have along its length?

A

Multiple RNA primers

49
Q

What does DNA pol I do?

A

Removes the RNA primers from the lagging strand and replaces them with DNA nucleotides

50
Q

What does DNA ligase do?

A

Joins the okazaki fragments together to form a continuous strand

51
Q

How does DNA ligase join okkazaki fragments?

A

By covalently joining the sugar phosphate backbones together with a phosphodiester bond

52
Q

What can DNA polymerase no do?

A

Initiate replication

53
Q

What must happen for DNA replication to occur?

A

An RNA primer must first be synthesised to provide an attachment point for DNA polymerase

54
Q

How do free nucleotides exist as?

A

Deoxynucleoside triphosphates

55
Q

What does DNA polymerase use the energy obtained from cleaving the two additional phosphates for?

A

To form a phosphodiester bond with the 3’ end of a nucleotide chain

56
Q

Why must DNA polymerase moved in opposite directions on the two strands?

A

Because double stranded DNA is antiparallel

57
Q

What must DNA polymerase do as it moves away from helicase?

A

Constantly return to copy newly separated stretches of DNA

58
Q

What are short fragments of copied DNA called?

A

Okazaki fragments

59
Q

What precedes each Okazaki fragment?

A

A primer

60
Q

What are primers replaced by?

A

DNA bases

61
Q

What combination joins fragments together?

A

DNA pol I and DNA ligase

62
Q

What is DNA sequencing?

A

The process of how the base order of a nucleotide sequence is elucidated

63
Q

What does the most widely used method for DNA sequencing involve?

A

The use of chain terminating dedddeoxynucleotides

64
Q

What do dideoxynucleotides lack?

A

The 3’ hydroxyl group needed to form a phosphodiester bond

65
Q

What do ddNTPs do?

A

Prevent the elongation of a nucleotide chain and terminate replication

66
Q

When using a ddNTP, what does the resulting length of a DNA sequence reflect ?

A

The nucleotide position where the dddNTP was incorporated

67
Q

What is the name of the method where dideoxynucleotides can be used to determine DNA sequence?

A

The Sanger method

68
Q

What is the result if the Sanger method is conducted on the coding strand?

A

The resulting sequence will be identical to the template strand

69
Q

As a typical PCR will generate over 1 billion DNA molecules, what should each PCR mix generate?

A

All the possible terminating fragments for that particular base

70
Q

What is the Sanger method?

A

Where four PCR mixes are set up, each containing stocks of normal nucleotides plus one dideoxynucleotides

71
Q

When the fragments are separated using gel electrophoresis, what can be determined and how?

A

The base sequence by ordering fragments according to length

72
Q

What happens in the Sanger method if a distinct radioactive or fluorescently labelled primer is included in each mix?

A

The fragments can be detected by automated sequencing machines

73
Q

What is the vast majority of the human genome comprised of?

A

Non-coding DNA

74
Q

What are the five different types of non-coding DNA?

A

Satellite DNA
Telomeres
Introns
Non-coding RNA genes
Gene regulatory sequences

75
Q

What is satellite DNA?

A

Tandemly repeating sequences of DNA which is a structural component of hétérochromosome and centromeres

76
Q

What is satellite DNA commonly used for?

A

DNA profiling

77
Q

What are telomeres?

A

Regions of repetitive DNA a the end of a chromosome

78
Q

What do telomeres protect against?

A

Chromosomal deterioration during replication

79
Q

What are introns?

A

Non-coding sequences within genes

80
Q

What removes introns and when?

A

RNA splicing prior to the formation of mRNA

81
Q

What are non-coding RNA genes?

A

Codes for RNA molecules that are not translated into protein

82
Q

What are gene regulatory sequences?

A

Sequences that are involve in the process of transcription

83
Q

What is DNA profiling?

A

A technique where individuals can be identified and compared via their respective DNA profiles

84
Q

What is within the non-coding regions of an individual genome?

A

Satellite DNA

85
Q

What is within the non-coding regions of an individual genome?

A

Satellite DNA

86
Q

What are the repeating elements of long stretches of DNA called?

A

Short tandem repeats

87
Q

What are the repeating elements of long stretches of DNA called?

A

Short tandem repeats

88
Q

How can tandem repeats be excised?

A

Using restriction enzymes

89
Q

How can tandem repeats be separated for comparison?

A

Gel electrophoresis

90
Q

Why will individual have unique DNA profiles?

A

As they will likely have different numbers of repeats at a given satellite DNA locus

91
Q

What will longer repeats generate?

A

Larger fragments

92
Q

What will shorter repeats generate?

A

Smaller fragments

93
Q

What is a Nucleosomes?

A

The structure of DNA packaged with histone proteins

94
Q

What is a Nucleosomes?

A

The structure of DNA packaged with histone proteins

95
Q

What do Nucleosomes help to do?

A

Supercool the DNA

96
Q

What do Nucleosomes help to do?

A

Supercoil the DNA

97
Q

What does Nucleosomes supercoiling the DNA result in?

A

A greatly compacted structure that allows for more efficient storage

98
Q

What does supercoiling help protect DNA from?

A

Damage

99
Q

What does supercoiling help protect DNA from?

A

Damage

100
Q

What does supercoiling allow chromosomes to do?

A

Be mobile during mitosis and meiosis

101
Q

How are Nucleosomes are linked?

A

By an additional histone protein

102
Q

How are Nucleosomes are linked?

A

By an additional histone protein

103
Q

What is linked Nucleosomes called?

A

Chromatismes

104
Q

What are linked Nucleosomes called?

A

Chromatosomes

105
Q

What do chromatosomes coil to form?

A

A solenoid structure

106
Q

What do solenoid structures condense to form?

A

30 nm fibre

107
Q

What do the 30nm fibre form?

A

Loops which are compressed and folded around a protein scaffold to form chromatin

108
Q

What do the 30nm fibre form?

A

Loops which are compressed and folded around a protein scaffold to form chromatin

109
Q

What does chromatin do to form what?

A

Supercoil during cell division to form chromosomes

110
Q

What is eight histone proteins called?

A

An octamer

111
Q

What does the negatively charged DNA associate with on the surface of the histone proteins?

A

Positively charged amino acids

112
Q

What do histone proteins have?

A

N-terminal tails

113
Q

What do n-terminal tails on histone proteins do?

A

Extrude outwards from the Nucleosomes

114
Q

What do tails and octamers do during chromosomal condensation?

A

Link up and draw the Nucleosomes closer together

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