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Biology 189 > DNA Structure & Replication > Flashcards

DNA Structure & Replication Flashcards

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1
Q

What does DNA stand for?

A

Deoxyribonucleic acid

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2
Q

What did Erwin Chargaff in 1950 report about DNA?

A

Erwin Chargaff reported that DNA composition varies from one species to the next. (This evidence of diversity made DNA a more credible candidate for the genetic material)

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3
Q

What are Nucleic Acids?

A

Nucleic Acids are polymers specialized for storage, transmission, and use of genetic material.

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4
Q

What is the monomer of DNA?

A

Nucleotides

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5
Q

What does a Nucleoside consist of?

A

Pentose sugar + N-containing base

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6
Q

What does a Nucleotide consist of?

A

Pentose sugar + N-containing base + Phosphate group

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7
Q

Are Pyrimidines single rings or double rings?

A

Single rings

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8
Q

Are Purines single rings or double rings?

A

double rings

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9
Q

Pyrimidines has Adenine and Guanine. True or False

A

False. Pyrimidines has Thymine and Cytosine

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10
Q

Purines has Adenine and Guanine. True or False

A

True.

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11
Q

What is the name of the DNA sugar?

A

Deoxyribose

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12
Q

What is Chargaff’s rule?

A

Chargaff’s rule state that in any species there is an equal number of A and T bases, and an equal number of G and C bases. (However, it was not known how the entire molecule fit together)

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13
Q

What did James Watson and Francis Crick introduce in 1953?

A

Watson and Crick introduced an elegant double-helical model for the structure of deoxyribonucleic acid/DNA. (They utilized Chargaff’s rule ad evidence from X-ray cystallography studies stolen from Rosalind Franklin)

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14
Q

When did Rosalind Franklin figure of the DNA model?

A

1953

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15
Q

At first, Watson and Crick thought the bases paired with A with A, and so on, but then changed their minds. Why?

A

Because such pairings did not fit the x-ray data, which suggested the double helix had a uniform diameter/width.

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16
Q

What happened after Watson and Crick paired a purine with a pyrimidine?

A

It resulted in a uniform width consistent with the X-ray data from Rosalind Franklin

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17
Q

purine + purine was too ________.

A

wide

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18
Q

Pyrimidine + Pyrimidine was too __________.

A

narrow

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19
Q

Purine + Pyrimidine was _________________________.

A

width consistent with X-ray data

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20
Q

Adenine pairs only with Thymine. True or False

A

True

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21
Q

Guanine only pairs with Cytosine. True or False

A

True

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22
Q

How did Watson-Crick explain the Chargaff’s rule model?

A

In any organism the amount of A =T and the amount of G = C

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23
Q

Why not Adenine and Cytosine or Thymine and Guanine?

A

Because of the way the hydrogen bond together (# of hydrogen bonds)

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24
Q

Enzymes only fit in the molecule in a ______________

A

specific direction

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25
Q

The 2 sugar-phosphate backbones are __________ in a DNA structure.

A

anti-parallel

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26
Q

Since the two strands of DNA are complementary, each strands acts as what?

A

It acts as a template for building a new strand in replication.

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27
Q

What happens in a DNA replication to the parent molecule?

A

The parent molecule unwinds, and two new daughter strands are built based on base-pairing rules.

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28
Q

Each parental strand can now serve as a what?

A

template for a new complementary strand

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29
Q

How is the parent molecule held by?

A

Its held by hydrogen bonding, so its easy to break apart.

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30
Q

The daughter DNA molecules, each consist of one ________ strand and one ____ strand.

A

parental and new strand.

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31
Q

Strands of DNA are _____ but very long.

A

thin

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32
Q

A human has ____ strands of DNA

A

48

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33
Q

A human has ____ pairs in our DNA structure.

A

24

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34
Q

What does Watson and Crick’s semiconservative model of replication predict?

A

when a double helix replicates, each daughter molecule will have one old strand (derived or “conserved” from the parent molecule) and one newly made strand.

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35
Q

What were the two competing models of the semiconservative model?

A
  1. Conservative model (the 2 parent strands rejoin)

2. Dispersive model (each strand is a mix of old and new)

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36
Q

What are the 4 things a cell needs to do a DNA replication?

A
  1. Energy
  2. Template (we need to copy an existing DNA strand)
  3. Enzymes (Many different enzymes)
  4. Nucleotides (Adenine, Guanine, Thymine. Cysteine)
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37
Q

Define Helicase (protein)

A

Unwinds parental double helix at replication forks

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38
Q

Define Single-strand binding protein (protein)

A

Binds to and stabilizes single-stranded DNA until it can be a template. (like a double dutch)

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39
Q

Define Topoisomerase (protein)

A

Relieves “overwinding” strain ahead of replication forks by breaking, swiveling, and rejoining DNA strands. (helps reduce the stress as we unwind it, but it can break)

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40
Q

Define Primase (protein)

A

Synthesizes an RNA primer at 5’ end of leading strand and of each Okazaki fragment ofl aging strand. (primer)

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41
Q

Define DNA pol III (protein)

A

Using parental DNA as a template, synthesizes new DNA strand by covalently adding nucleotides to the 3’ end of pre-existing DNA strand or RNA primer. (forming phosphates groups)

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42
Q

Define DNA pol I (protein)

A

Removes RNA nucleotides of primer from 5’ end and replaces them with DNA nucleotides. (removal of primers)

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43
Q

Define DNA ligase (protein)

A

Joins 3’ end of DNA that replaces primer to rest of leading strand and joins Okazaki fragments of lagging strand.

44
Q

Where does the DNA replication begin at?

A

origins of replication.

45
Q

What is origins of replication?

A

where the two DNA strands are separated, opening up a replication “bubble” and separating the bases of hydrogen bonds.

46
Q

How many origins of replication does a eukaryotic chromosome have?

A

It may have hundreds or even thousands.

47
Q

How does DNA replication proceed?

A

In both directions from each origin, until the entire molecule is copied. (trying to make 2 strands, like a highway, one way goes one way as the other goes the opposite way)

48
Q

The top strand of a DNA will be __________ to come out than the ______ because of the helicase.

A

easier

end

49
Q

You cannot start a DNA replication until you add a _______.

A

RNA primer (single stranded)

50
Q

Why start with a RNA primer and not DNA?

A

because a DNA can copy its own very fast and RNA cannot.

51
Q

DNA polymerases cannot initiate synthesis of a polynucleotide; they can only add nucleotides to the ___’ end.

A

3’end.

52
Q

The initial nucleotide strand is a short ______

A

RNA primer

53
Q

What is primase?

A

Its an enzyme that can start an RNA chain from scratch and adds RNA nucleotides one at a time using the parental DNA as a template

54
Q

How short is the primer? Why?

A

5-10 nucleotides long, and the 3’ end serves as the staring point for the new DNA strand. It is short because it is just getting started.

55
Q

At the end of each replication bubble is a _____________, a Y-shaped region where new DNA strands are elongating

A

replication fork

56
Q

What is a replication fork?

A

is a point in a DNA molecule where the 2 strands separate during replication

57
Q

What is a DNA polymerases?

A

Its an enzyme that catalyzes the elongation of new DNA at a replication fork

58
Q

Most DNA polymerases require a ______ and a DNA _____________

A

primer*

template strand*

59
Q

The rate of elongation is how many per second in bacteria?

A

500 nucleotides

60
Q

The rate of elongation is how many per second in human cells?

A

50 nucleotides

61
Q

Ecoli can replicate every ___ minutes

A

20

62
Q

We have thousands of DNA and bacteria only has 20 to 25 of DNA. Which is easy to replicate?

A

bacteria

63
Q

The antiparallel structure of the double helix affects replication. Why?

A

It leads to the lagging and leading strand.

64
Q

DNA polymerases add nucleotides only to the free ___ end of a growing strand

A

3’

65
Q

DNA polymerases add nucleotides only to the free 3’ end of growing strand, therefore A new DNA strand can elongate ONLY in the ___ to ___’ direction

A

5’ *

3’ *

66
Q

How is the leading strand started?

A

Along one template strand of DNA, the DNA polymerase synthesizes a leading strand continuously, moving toward the replication fork.

67
Q

How does the lagging strand elongate toward the other new strand?

A

DNA polymerase must work in the direction away from the replication fork

68
Q

How is the lagging strand synthesized?

A

as a series of segments called Okazaki fragments, which are joined together by DNA ligase.

69
Q

DNA polymerases proofread newly made DNA, replacing any incorrect ____________

A

nucleotides

70
Q

What happens in a mismatch repair of DNA?

A

it repairs enzymes correct errors in base pairing.

71
Q

How can DNA be damaged?

A

By exposure to harmful chemical or physical agents such as cigarette smoke and x rays; it can also undergo spontaneous changes(very rare 10 to the 6)

72
Q

What happens in a nucleotide excision repair?

A

an important process cells use to correct many different types of DNA damage. The nuclease cuts out and replaces damaged’ stretches of DNA

73
Q

Why would bacteria beat us in reproduction?

A

They can duplicate every 20 minutes

74
Q

cells can only be damaged in _____________

A

cell division

75
Q

Error rate after proofreading repair is low but not _____

A

zero

76
Q

sequence changes may become permanent and can be passed on to the next ___________

A

generation (egg and sperm)

77
Q

These changes (mutations) are the source of the genetic variation upon which ________________ operates

A

natural selection

78
Q

During replication, the direction of synthesis of the new DNA on the leading strand and lagging strand is?

A

5’ to 3’ only.

79
Q

How many hydrogen bonds does Adenine and thymine have?

A

2 hydrogen bonds (easy to break)

80
Q

How many hydrogen bonds does guanine and cytosine have?

A

3 hydrogen bonds

81
Q

Cytosine and thymine are pyrimidine which have 6 atoms. Name them.

A

4 carbon and 2 nitrogen

82
Q

The 5’ carbon has a ___________ group attached to it.

A

phosphate group

83
Q

The 3’ carbon a _________ group

A

hydroxyl group

84
Q

Adenine and guanine are purines, How many atoms do they have?

A

5 carbon and 4 nitrogen

85
Q

The hydroxyl groups on the _____and ____carbons link to the phosphate groups to form the DNA backbone

A

5’- and 3’-

86
Q

why are the strands of DNA molecule said to be complementary?

A

because each strand can be used to make the other strand

87
Q

Name the enzyme that joins individual nucleotides to produce a new strand of DNA

A

DNA polymerase

88
Q

The principal enzyme involved in DNA replication is called?

A

DNA polymerase

89
Q

The enzyme that proofreads each new DNA strand so that each molecule is a near-perfect copy of the original is ________

A

DNA polymerase

90
Q

DNA polymerase CANNOT initiate synthese of a polynucleotide, they can only ____ nucleotides to the ___ end, The initial nucleotide strand is a short RNA primer.

A
  • add

* 3’

91
Q

Nucleotide can only be added to the end of 3’ prime. Why?

A

the shape of the enzyme

92
Q

A primer is made of?

A

RNA

93
Q

Enzymes called ________ catalyze the elongation of new DNA at a replication fork

A

DNA polymerases

94
Q

Most DNA polymerases require a ______ and a DNA ______ strand.

A
  • Primer

* Template

95
Q

DNA ligase joins 3’ end of DNA that replaces primer to rest of leading strand and joins _______ of lagging strand

A

Okcazaki fragments

96
Q

What does it mean when DNA polymerases proofread?

A

They proofread newly made DNA, replacing any incorrect nucleotides.

97
Q

What happens in a mismatch repair of DNA?

A

Repair enzymes correct errors in base pairing.

98
Q

What holds the double helix of DNA?

A

Covalent bonds

99
Q

What holds the sides of a double helix of DNA?

A

hydrogen bonds

100
Q

Limitations of DNA polymerase create problems for the linear DNA of ________ chromosomes

A

eukaryotic

101
Q

The usual replication machinery provides no way to complete the 5’ ends, which means?

A

repeated rounds of replication produce shorter DNA molecules with uneven ends.

102
Q

The usual replication machinery provides no way to complete the 5’ ends, so repeated rounds of replication produce shorter DNA molecules with uneven ends. Why is this not a problem with prokaryotes?

A

most have circular chromosomes

103
Q

Every time your DNA replicates, your DNA gets longer. True or False

A

False. It gets shorter and shorter

104
Q

Define chronological age

A

The age you are right now.

105
Q

Define Biological age

A

how many times your cell is divided

106
Q

Why does DNA replicate?

A
  1. For growth and repair of the existing structure. (you)

2. To produce gametes (baby)

Biology 189 (1 decks)

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