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Biology HL - IB > DNA replication > Flashcards

DNA replication Flashcards

1
Q

What is DNA replication?

A

DNA replication is the process of producing exact copies of DNA with identical base sequences.

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2
Q

Why is DNA replication essential for multicellular organisms?

A

DNA replication is required for reproduction, growth, and tissue replacement.

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3
Q

What is the result of DNA replication?

A

The result is two identical DNA molecules, each containing one original strand and one newly synthesized strand.

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4
Q

What is the role of base pairing in DNA replication?

A

Base pairing ensures that the new DNA strands are complementary to the original strands, maintaining identical sequences.

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5
Q

Which enzymes are primarily involved in DNA replication?

A

Key enzymes include DNA helicase (unwinds the DNA), DNA polymerase (synthesizes new strands), and DNA ligase (joins Okazaki fragments).

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6
Q

What happens during the initiation phase of DNA replication?

A

The double helix unwinds and separates at specific locations called origins of replication.

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7
Q

How does the elongation phase of DNA replication occur?

A

New nucleotides are added to the growing DNA strand by DNA polymerase, following the rules of base pairing.

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8
Q

What is the significance of proofreading during DNA replication?

A

Proofreading by DNA polymerase helps correct errors, ensuring high fidelity in the replicated DNA.

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9
Q

What is semi-conservative replication?

A

Semi-conservative replication means that each new DNA molecule consists of one old strand and one new strand.

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10
Q

How does DNA replication contribute to genetic continuity?

A

Accurate DNA replication ensures that genetic information is faithfully passed on to daughter cells during cell division.

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11
Q

What does the term “semi-conservative” mean in DNA replication?

A

Semi-conservative means that each new DNA molecule consists of one original strand and one newly synthesized strand.

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12
Q

How does complementary base pairing contribute to the accuracy of DNA replication?

A

Complementary base pairing ensures that each new strand is an exact copy of the original, maintaining identical base sequences.

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13
Q

What are the base pairing rules in DNA?

A

Adenine (A) pairs with Thymine (T), and Cytosine (C) pairs with Guanine (G).

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14
Q

Why is high accuracy important in DNA replication?

A

High accuracy is crucial to prevent mutations, which can lead to genetic disorders or malfunctioning proteins.

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15
Q

What role do enzymes play in the semi-conservative nature of DNA replication?

A

Enzymes like DNA polymerase facilitate the addition of nucleotides, ensuring proper base pairing and synthesis of new strands.

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16
Q

What happens if there is a mistake during DNA replication?

A

If there is a mistake, it can lead to mutations; however, proofreading mechanisms help correct these errors.

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17
Q

How does the structure of DNA support its semi-conservative replication?

A

The double helix structure allows each strand to serve as a template for the synthesis of a new complementary strand.

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18
Q

What is the significance of having identical base sequences after replication?

A

Identical base sequences ensure that genetic information is accurately passed on during cell division, maintaining organismal traits.

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19
Q

How does the process of unwinding DNA contribute to semi-conservative replication?

A

Unwinding creates two single strands that serve as templates for synthesizing new complementary strands.

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20
Q

Why is it important for students to understand the semi-conservative nature of DNA replication?

A

Understanding this concept provides insight into how genetic information is preserved and transmitted across generations in living organisms.

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21
Q

What is the role of helicase in DNA replication?

A

Helicase unwinds the DNA double helix and breaks the hydrogen bonds between the two strands.

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22
Q

How does helicase initiate DNA replication?

A

Helicase binds to the origin of replication and separates the two strands of DNA, creating a replication fork.

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23
Q

Why is the action of helicase important for DNA replication?

A

By unwinding the DNA, helicase allows access for other enzymes, such as DNA polymerase, to synthesize new strands.

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24
Q

What is the general role of DNA polymerase in DNA replication?

A

DNA polymerase synthesizes new DNA strands by adding nucleotides complementary to the template strand.

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25
Q

How does DNA polymerase ensure accuracy during replication?

A

DNA polymerase follows base-pairing rules (A with T and C with G) to ensure that nucleotides are added correctly.

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26
Q

What happens if there is an error during DNA synthesis by DNA polymerase?

A

If an error occurs, DNA polymerase has proofreading activity that can detect and correct mistakes.

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27
Q

What type of strands do DNA polymerases synthesize?

A

DNA polymerases synthesize new strands in a 5’ to 3’ direction.

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28
Q

What is the significance of both helicase and DNA polymerase working together?

A

The coordinated action of helicase unwinding the DNA and DNA polymerase synthesizing new strands is essential for accurate and efficient DNA replication.

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29
Q

In which phase of the cell cycle does DNA replication occur?

A

DNA replication occurs during the S phase (synthesis phase) of interphase.

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30
Q

Why do cells need to replicate their DNA?

A

Cells replicate their DNA to ensure that each daughter cell receives an identical copy of the genetic material during cell division.

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31
Q

What is the polymerase chain reaction (PCR)?

A

PCR is a technique used to amplify specific DNA sequences, producing millions of copies from a small initial sample.

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32
Q

What role do primers play in PCR?

A

Primers are short sequences of nucleotides that bind to specific regions of the DNA template, providing a starting point for DNA synthesis.

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33
Q

Why are temperature changes important in PCR?

A

Temperature changes are essential for denaturation (separating DNA strands), annealing (binding primers), and extension (synthesizing new DNA strands).

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34
Q

What is the function of Taq polymerase in PCR?

A

Taq polymerase is a heat-stable enzyme that synthesizes new DNA strands by adding nucleotides to the primers during the extension phase.

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35
Q

What occurs during the denaturation step of PCR?

A

The double-stranded DNA is heated to around 94-98°C, causing the hydrogen bonds to break and the strands to separate.

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36
Q

What happens during the annealing step of PCR?

A

The temperature is lowered (usually to 50-65°C) to allow primers to bind or anneal to their complementary sequences on the single-stranded DNA.

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37
Q

What occurs during the extension step of PCR?

A

The temperature is raised to about 75°C, allowing Taq polymerase to synthesize new DNA strands by adding nucleotides to the primers.

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38
Q

How many cycles are typically performed in PCR?

A

Typically, 25-35 cycles are performed, resulting in exponential amplification of the target DNA sequence.

39
Q

What is gel electrophoresis used for?

A

Gel electrophoresis is used to separate and visualize DNA fragments based on their size by applying an electric current through a gel matrix.

40
Q

How does gel electrophoresis separate DNA fragments?

A

Smaller DNA fragments move faster through the gel matrix than larger ones, allowing for separation based on size.

41
Q

What is the significance of using gel electrophoresis after PCR?

A

Gel electrophoresis allows researchers to confirm that the desired DNA fragment has been successfully amplified and to analyze its size.

42
Q

What type of gel is commonly used in electrophoresis?

A

Agarose gel is commonly used for separating DNA fragments in gel electrophoresis due to its porous nature.

43
Q

How can DNA bands be visualized after gel electrophoresis?

A

DNA bands can be visualized using a staining dye, such as ethidium bromide or SYBR Green, which fluoresces under UV light.

44
Q

Why is PCR considered a powerful tool in molecular biology?

A

PCR allows for rapid amplification of specific DNA sequences, enabling various applications such as cloning, sequencing, and forensic analysis.

45
Q

What is the polymerase chain reaction (PCR) used for?

A

PCR is used to amplify specific DNA sequences, producing millions of copies from a small sample.

46
Q

What is one major application of PCR in forensic science?

A

PCR is used in DNA profiling to identify individuals based on their unique genetic markers.

47
Q

How is PCR utilized in paternity testing?

A

PCR amplifies specific DNA regions to compare genetic markers between a child and potential parents, determining biological relationships.

48
Q

What role does gel electrophoresis play in DNA analysis?

A

Gel electrophoresis separates DNA fragments based on size, allowing visualization and comparison of amplified DNA from PCR.

49
Q

Why is increasing the number of markers important in DNA profiling?

A

Increasing the number of markers reduces the probability of a false match, enhancing the reliability of the results.

50
Q

In addition to forensic investigations, what other fields benefit from PCR?

A

PCR is used in medical diagnostics, genetic research, and environmental monitoring.

51
Q

How does gel electrophoresis help confirm successful PCR amplification?

A

By visualizing the size of the amplified DNA fragments, researchers can confirm that the correct target sequence has been amplified.

52
Q

What is a common use of PCR in medical diagnostics?

A

PCR is used to detect the presence of pathogens, such as viruses or bacteria, in clinical samples.

53
Q

How does the reliability of PCR results improve with multiple measurements?

A

Reliability is enhanced by repeating tests or using multiple markers, which increases confidence in the accuracy of the results.

54
Q

What are some limitations of PCR and gel electrophoresis?

A

Limitations include potential contamination leading to false positives and the requirement for specific primers for target amplification.

55
Q

What is the directionality of DNA strands?

A

DNA strands have a directionality defined by their 5’ and 3’ terminals.

56
Q

What does the 5’ end of a DNA strand signify?

A

The 5’ end has a phosphate group attached to the fifth carbon of the sugar molecule.

57
Q

What does the 3’ end of a DNA strand signify?

A

The 3’ end has a hydroxyl group (-OH) attached to the third carbon of the sugar molecule.

58
Q

How do DNA polymerases add nucleotides during DNA replication?

A

DNA polymerases add nucleotides to the 3’ end of a growing DNA strand, using the 5’ end of incoming nucleotides.

59
Q

Why is it important for DNA poymerases to add nucleotides in this direction?

A

Adding nucleotides to the 3’ end ensures that the new strand grows in a 5’ to 3’ direction, which is essential for proper DNA synthesis.

60
Q

What happens if a nucleotide is added incorrectly during replication?

A

Incorrectly added nucleotides can lead to mutations, but DNA polymerases have proofreading mechanisms to correct errors.

61
Q

Why do DNA strands have antiparallel orientation?

A

The two strands of DNA run in opposite directions (one 5’ to 3’, the other 3’ to 5’), allowing for complementary base pairing and stability.

62
Q

How does the directionality of DNA polymerases affect leading and lagging strand synthesis?

A

The leading strand is synthesized continuously in the 5’ to 3’ direction, while the lagging strand is synthesized in short fragments (Okazaki fragments) also in the 5’ to 3’ direction but away from the replication fork.

63
Q

What is the significance of understanding DNA polymerase directionality in molecular biology?

A

Understanding directionality is crucial for grasping how DNA replication occurs and how genetic information is accurately transmitted during cell division.

64
Q

What type of bond forms between nucleotides during DNA synthesis?

A

Phosphodiester bonds form between the phosphate group of one nucleotide and the hydroxyl group of another, linking them together in a growing strand.

65
Q

What is the main difference between replication on the leading strand and the lagging strand?

A

The leading strand is synthesized continuously, while the lagging strand is synthesized discontinuously.

66
Q

What does “continuous” replication mean in the context of the leading strand?

A

Continuous replication means that nucleotides are added in a smooth, uninterrupted manner as the DNA unwinds.

67
Q

What does “discontinuous” replication mean for the lagging strand?

A

Discontinuous replication means that nucleotides are added in short segments, known as Okazaki fragments, due to the opposite direction of synthesis.

68
Q

What are Okazaki fragments?

A

Okazaki fragments are short sequences of DNA synthesized on the lagging strand during DNA replication.

69
Q

How many RNA primers are needed for replication on the leading strand?

A

Only one RNA primer is needed to initiate replication on the leading strand.

70
Q

How many RNA primers are required for replication on the lagging strand?

A

Multiple RNA primers are required for each Okazaki fragment on the lagging strand.

71
Q

Why is the leading strand synthesized continuously?

A

The leading strand is synthesized continuously because it runs in the same direction as the replication fork, allowing for smooth addition of nucleotides.

72
Q

Why does the lagging strand require multiple initiation points?

A

The lagging strand runs in the opposite direction of the replication fork, necessitating multiple initiation points for synthesizing Okazaki fragments.

73
Q

What happens to Okazaki fragments after they are synthesized?

A

Okazaki fragments are later joined together by DNA ligase to form a continuous DNA strand.

74
Q

How does understanding these differences in replication contribute to our knowledge of DNA biology?

A

Understanding these differences helps explain how DNA replication is accurately and efficiently completed, ensuring genetic fidelity during cell division.

75
Q

What is the role of DNA primase in prokaryotic DNA replication?

A

DNA primase synthesizes short RNA primers that provide a starting point for DNA synthesis.

76
Q

Why are RNA primers necessary for DNA replication?

A

RNA primers are necessary because DNA polymerases cannot initiate synthesis without a pre-existing strand.

77
Q

What is the function of DNA polymerase III in prokaryotic replication?

A

DNA polymerase III is the primary enzyme responsible for synthesizing new DNA strands by adding nucleotides to the 3’ end of the RNA primer.

78
Q

How does DNA polymerase III ensure accuracy during replication?

A

DNA polymerase III has proofreading activity that allows it to correct errors during nucleotide incorporation.

79
Q

What is the role of DNA polymerase I in prokaryotic replication?

A

DNA polymerase I removes RNA primers and replaces them with DNA nucleotides, ensuring that the final strand is entirely composed of DNA.

80
Q

How does DNA polymerase I contribute to the overall process of replication?

A

By replacing RNA primers with DNA, it helps maintain the integrity of the newly synthesized DNA strand.

81
Q

What is the function of DNA ligase in prokaryotic replication?

A

DNA ligase joins Okazaki fragments on the lagging strand by forming phosphodiester bonds between adjacent nucleotides.

82
Q

Why is the action of DNA ligase important?

A

The action of DNA ligase is crucial for creating a continuous and intact DNA strand after replication, particularly on the lagging strand.

83
Q

How do these enzymes work together during prokaryotic replication?

A

These enzymes collaborate to initiate synthesis (primase), extend strands (DNA polymerase III), replace primers (DNA polymerase I), and seal gaps (DNA ligase), ensuring accurate and efficient replication.

84
Q

What is the significance of understanding these enzymes in molecular biology?

A

Understanding these enzymes provides insight into the mechanisms of DNA replication, which is fundamental to genetics and cell biology.

85
Q

What is the primary function of DNA proofreading?

A

DNA proofreading ensures the accuracy of DNA replication by correcting mismatched nucleotides.

86
Q

Which enzyme is primarily responsible for proofreading during DNA replication?

A

DNA polymerase III is responsible for proofreading and correcting errors in nucleotide incorporation.

87
Q

How does DNA polymerase III identify mismatched bases?

A

DNA polymerase III detects mismatched bases at the 3’ terminal of the growing DNA strand.

88
Q

What action does DNA polymerase III take when it finds a mismatched base?

A

DNA polymerase III removes the incorrectly paired nucleotide from the 3’ terminal.

89
Q

After removing a mismatched nucleotide, what does DNA polymerase III do next?

A

DNA polymerase III replaces the removed nucleotide with the correctly matched nucleotide.

90
Q

Why is proofreading important during DNA replication?

A

Proofreading is crucial for maintaining genetic fidelity and preventing mutations that could lead to diseases or malfunctions.

91
Q

What happens if errors are not corrected during DNA replication?

A

Uncorrected errors can lead to mutations, which may result in genetic disorders or cancer.

92
Q

How does the proofreading activity of DNA polymerase III contribute to overall replication accuracy?

A

The proofreading activity significantly increases the fidelity of DNA replication, ensuring that most errors are corrected before the new strand is completed.

93
Q

In what direction does DNA polymerase III add nucleotides during synthesis?

A

DNA polymerase III adds nucleotides in the 5’ to 3’ direction.

94
Q

What is the significance of understanding DNA proofreading in molecular biology?

A

Understanding DNA proofreading provides insight into the mechanisms that preserve genetic integrity and prevent mutations during cell division.

Biology HL - IB (29 decks)

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