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Molecular Biology and Genetics > DNA Replication and Chromosomes > Flashcards

DNA Replication and Chromosomes Flashcards

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1
Q

What did the 3-dimensional crystal structure *proposed by Watson ad Crick suggested?

A

How DNA could be replicated to maintain the genetic information.

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2
Q

What could each strand of DNA do?

A

Separated.

Used as the template for second strand production.

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3
Q

What should DNA duplex be before any synthesis begins?

A

Unwound.

Melted apart.

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4
Q

With what do enzymes need to deal?

A

With the 5’-3’ orientation of each of the DNA strands.

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5
Q

In what do the 3 replication models of DNA differ?

A

In terms of how much old and new DNA daughter cells contain.

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6
Q

What were the thoughts of DNA helix unwound and replication?

A

Unclear if it would happen along the entire bacterial chromosome in one go.
If it had to be done in multiple smaller sections.

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7
Q

How could the 3 competing models of DNA replication be tested based on Meselson and Stahl?

A

By labelling Escherichia coli DNA during replication with nitrogen isotopes.

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8
Q

Where did incorporation of 14N resulted?

A

In light DNA.

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9
Q

Where did use of 15N resulted?

A

In heavier DNA.

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10
Q

How could light and heavy DNA be separated?

A

By ultra-centrifugation.

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11
Q

Where is DNA centrifuged?

A

In a CsCl gradient.

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12
Q

What happens to DNA when it is centrifuged in a CsCl gradient?

A

It moves towards neutral buoyancy point.

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13
Q

Which are the 3 models of DNA strands?

A

Conservative.
Semi-conservative.
Dispersive.

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14
Q

What happened in Meselson-Stahl experiment?

A

Several generations of bacteria went through it.

Chromosomal DNA became increasingly ‘light’.

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15
Q

When is replicating/synthesising DNA simple?

A

When a single template strand is provided.

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16
Q

What happens while the double-stranded DNA is replicated?

A

One strand is in the opposite direction to the other.

The 2 DNA Polymerases collide.

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17
Q

How do the cells avoid the 2 DNA Polymerases from colliding?

A

By flexing one of the 2 strands around.

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18
Q

What happens to the 2 DNA Polymerases when the cells flex one of them around?

A

They move in the same direction as a single ‘DNA synthesis/replication machine’.

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19
Q

For what is a replication complex/machine responsible?

A

DNA replication in vivo.

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20
Q

What does the replication complex/machine generate?

A

Copies of whole chromosomes in each cell cycle.

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21
Q

What does DNA Polymerase synthesize?

A

New DNA.

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22
Q

What does DNA Polymerase catalyse?

A

Formation of phosphodiester bond between 3’-OH of DNA strand synthesized and incoming 5’-triphosphate (dNTP).

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23
Q

What does the parental DNA strand provide?

A

The template for base pairing.

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24
Q

From where does the energy for the parental DNA providing the template come from?

A

The removal of pyrophosphate from incoming dNTP.

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25
Q

What must be free for the parental DNA providing the template?

A

3’OH group.

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26
Q

In which direction does polymerisation always occur?

A

In 5’–>3’.

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27
Q

What does DNA Polymerase test?

A

Each new dNTP.

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28
Q

What does DNA Polymerase required?

A

The correct base pairing before moving to the next base.

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29
Q

What is the direction of DNA Polymerase activity?

A

3’-5’.

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30
Q

How is the activity of DNA Polymerase named?

A

Exonuclease.

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31
Q

What does the exonuclease activity 3’-5’ of DNA Polymerase allow it to do?

A

Remove a mistake.

Replace the wrong nucleotide with the correct one.

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32
Q

What do RNA primers initiate?

A

DNA synthesis.

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33
Q

What does DNA Polymerase need to begin polymerisation?

A

A 3’-OH group.

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34
Q

What can DNA Primase start, without requiring starting point?

A

An RNA-based polynucleotide chain.

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35
Q

What does DNA Primase provide?

A

A ‘primer’ for DNA Polymerase.

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36
Q

What does primases uses instead of deoxyribonucleotides?

A

Ribonucleotides.

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37
Q

For how long does Primase function?

A

For only very short time.

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38
Q

Why does primase function for only a very short time?

A

Because RNA is unstable.

NTPs are limited.

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39
Q

How long is the primer?

A

Around 10 nucleotides long.

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40
Q

What does primase incorporate?

A

dNTPs.

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41
Q

Why does primase incorporates dNTPs?

A

To provide a stronger synthesis scaffold.

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42
Q

By what can DNA Polymerase synthesize DNA?

A

From the leading strand.

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43
Q

What is the characteristic of the other/lagging strand of DNA?

A

It is in the ‘wrong’ orientation than the leading strand.

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44
Q

How is the problem of wrong orientation of lagging strand synthesis fixed?

A

By breaking down the synthesis into small sections.

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45
Q

Which are the small sections lagging strand break down to?

A

Okazaki fragments.

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46
Q

How are Okazaki fragments linked together?

A

By DNA ligase.

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47
Q

What do helicases unwind?

A

The parental double helix.

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48
Q

What do single-strand binding proteins stabilise?

A

The unwound parental DNA.

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49
Q

From what are the 2 parental strands of DNA replicated?

A

By 2 DNA Polymerases.

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50
Q

Where are the 2 parental strands of DNA while they are replicated by 2 DNA Polymerases?

A

In a single replication machine.

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51
Q

Where does e single replication machine travel during DNA replication by DNA Polymerases?

A

Along the parental DNA duplex.

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52
Q

What does the single replication machine do to the parental DNA duplex?

A

Unwinding.

Melting as goes.

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53
Q

In what are origin (Ori) sequences rich?

A

AT base pairs.

54
Q

Where does a family of initiator proteins gather?

A

At Ori sites of DNA.

55
Q

When does a family of initiator proteins gather at Ori sites of DNA?

A

At beginning of S-phase.

56
Q

Why does a family of initiator proteins gather at Ori sited of DNA at the beginning of S-phase?

A

To trigger synthesis.

=Activate replication machine.

57
Q

Which chromatin is replicated first in DNA?

A

The least condensed chromatin.

58
Q

Where does DNA replication start?

A

At Ori sequences of DNA.

59
Q

Where does DNA replication move after Ori sequences?

A

Out in both directions.

60
Q

What do large chromosomes have?

A

Multiple origins .

61
Q

Why do large chromosomes have multiple origins?

A

To reduce the time of replication in all the DNA before cell division.

62
Q

What is DNA?

A

A very long polymer.

63
Q

Where does DNA need to be packaged?

A

Inside the cell.

64
Q

Why does DNA need to be packaged inside the cell?

A

For safety.

65
Q

How else does DNA need to be?

A

Readily unpacked.

66
Q

Why does DNA need to be readily unpacked?

A

For replication.

Gene expression.

67
Q

Where is DNA wrapped?

A

Around specialised proteins.

68
Q

How are the specialised proteins, DNA is wrapped around, called?

A

Histones.

69
Q

What does DNA form when it is wrapped around histones?

A

Nucleosomes + ‘beads on a string’.

70
Q

What happens to nucleosomes and ‘beads on a string’ formed by DNA wrapped around histones?

A

It is further coiled and folded.

71
Q

Why is nucleosomes + ‘beads on a string’ further coiled and folded?

A

To reduce size.

To regulate gene expression.

72
Q

In what does higher order packing result?

A

In chromosome structures.

73
Q

How can the chromosome structures be visualised?

A

By light microscopy.

74
Q

Into what are the ‘beads on a string’ supercoiled?

A

Into a helical fibre.

75
Q

On what is the helical fibre, formed by supercoiled ‘beads on a string’, looped?

A

On a chromosome protein scaffold.

76
Q

What happens to the helical fibre after it is looped on a chromosome protein scaffold?

A

It is coiled agai.

77
Q

Why is a helical fibre coiled again after it is looped on a chromosome protein scaffold?

A

To form the chromosome.

78
Q

What is the Histone H1?

A

A ‘Locking unit’.

79
Q

What does Histone H1 do?

A

It locks a loop of DNA around the main body of the nucleosome.

80
Q

Of what is the main body of the nucleosome composed?

A

An octamer of 4 different histones.

81
Q

Which are the 4 different histones of what the main body of the nucleosome is composed?

A

H2A.
H2B.
H3.
H4.

82
Q

What do specific DNA sequences determine?

A

Which sections of DNA are associated with histones.

Which parts of DNA form the links between nucleosomes.

83
Q

When do nucleosomes repeat?

A

Approximately every 200bp.

84
Q

Why do nucleosomes repeat approx. every 200bp?

A

To form the ‘beads on a string’.

85
Q

Of what does one nucleosome consist?

A

A DNA segment –> wrapped around a drum-shaped nucleosome core –> containing 8 histones –> locked in place by a 9th histone.

86
Q

How can nucleosomes be removed and repositioned?

A

By replacing/modifying H1 linker protein.

87
Q

Why can nucleosomes be removed and repositoned?

A

To expose/hide particular DNA sequences –> effect gene expression.

88
Q

What can the effect of gene expression, due to hidden/exposed DNA sequences by nucleosome remodelling, be?

A

Cross-generational.

Inherited.

89
Q

Is the nucleosome remodelling encoded by DNA?

A

No.

90
Q

What must happen to a newly replicated DNA?

A

It must be repackaged.

91
Q

Where are histone proteins made?

A

During S-phase.

92
Q

Where are nucleosomes gathered?

A

Behind the replication machine.

93
Q

What are the parental histone proteins?

A

Re-cycled.

94
Q

How are the re-cycled parental histone proteins used?

A

New histones –> mixed with –> parent histones: in new nucleosomes.

95
Q

What do new histones mixed with parental histones produce?

A

Completely new, mixed, and old nucleosomes.

96
Q

How is the production of completely new nucleosomes from new histones mixed with parent histones called?

A

Effectively semi-conservative and conservative replication.

97
Q

What does the highest order of DNA packing produce?

A

The ‘classical’ chromosome structure.

98
Q

Where is the ‘classical’ chromosome structure seen?

A

Only during cell division.

99
Q

Why is the ‘classical’ chromosome structure seen only during cell division?

A

Replicated chromosomes –> separated inot –> daughter cells.

100
Q

What is used to identify chromosomes?

A

Chromosome size.

Banding patterns.

101
Q

Where to genetic problem lead some times?

A

To disease.

102
Q

How many autosomal chromosome pairs and sex chromosome pairs do humans normally have?

A

22 autosomal.

2 sex.

103
Q

Between which organisms does the number of autosomal and sec chromosome pairs vary?

A

Mammals.
Animals.
Eukaryotes.

104
Q

Is DNA always found in the ‘classical’ chromosomes?

A

No.

105
Q

How is the DNA packed in the nucleus for most of the cell cycle?

A

Less well-packed.

106
Q

What does the less well-packing of DNA in the nucleus for most of the cell cycle form after staining?

A

Light and dark bands.

107
Q

What is chromatin?

A

The relaxed structure chromosomal DNA adopts in nucleus.

108
Q

When does DNA adopt chromatin relaxed structure?

A

When DNA it is not in the condensed chromosomes form.

109
Q

What happens during DNA replication to each chromosome?

A

They are duplicated.

110
Q

What does each chromosome form once it is dulicated?

A

‘X’ chromosome structure.

111
Q

What does an individual have?

A

A copy of chromosomes from each parent.

112
Q

How are the copies of chromosomes form each parent called?

A

‘Chromosome pairs’.

113
Q

What do ‘chromosome pairs’ have?

A

Very similar sequences.

114
Q

What can the very similar sequences of ‘chromosome pairs’ do?

A

Recombine.

115
Q

What can the very similar sequences of ‘chromosome pairs’ give when they recombine?

A

Allele combinations.

116
Q

What is ‘Karyotyping’?

A

A diagnostic technique.

117
Q

What can the ‘Karyotyping’ identify?

A

Genetic disorders.
Developmental abnormalities.
Cancers.

118
Q

Where do genetic disorders identified by ‘karyotyping’ occur?

A

Through large-scale re-arrangement of chromosomal sections.

119
Q

What is the characteristic of the ‘Edwards syndrome’?

A

Trisomy at chromosome 18.

120
Q

How else is he ‘Edwards syndrome’ called?

A

Trisomy 18.

121
Q

Where does ‘Edwards syndrome’ result?

A

In severe developmental problems.

Neonatal death.

122
Q

How can ‘a-thalassaemia mental retardation syndrome’ called?

A

(ATR-16).

123
Q

Based on which characteristics can chromosomes be identified?

A

Size.
Shape.
Banding patterns.

124
Q

What did recombination and physical maps allow?

A

Isolation of specific sequences.
Investigation of gene function.
Mutations’ effect.

125
Q

Why can chromosomes not be manipulated to investigate gene structure and function?

A

They are far too big.

126
Q

What did they need to do to investigate gene structure and function?

A

Produce smaller segments of chromosome with 1/few genes for experiments in a model organism like E. coli.

127
Q

When did the multi-disciplinary study of gene function begin?

A

In 1970.

128
Q

How did the multi-disciplinary study of gene function begin?

A

Through collaboration of biochemistry and genetic.

129
Q

How do we know the multi-disciplinary study of gene function, today?

A

‘Molecular biology’.

130
Q

What did key enzymes allow?

A

Gene cloning.
DNA sequencing.
PCR development.

131
Q

Where was PCR used?

A

Genetic engineering.
Genetic diagnostics.
Forensic profiling.

Molecular Biology and Genetics (15 decks)

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