DNA Replication & Repair
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Questions and Answers

DNA replication occurs during the ______ phase of the cell cycle.

S

The first stage of DNA replication is called ______.

Initiation

During DNA replication, the ______ strand is synthesized continuously.

leading

The enzyme that unwinds the DNA double helix is called ______.

<p>Helicase</p> Signup and view all the answers

In bacterial DNA replication, nucleotides are added by ______.

<p>DNA pol III</p> Signup and view all the answers

The ______ strand is synthesized in short segments known as Okazaki fragments.

<p>lagging</p> Signup and view all the answers

RNA primers are synthesized by an enzyme called ______.

<p>Primase</p> Signup and view all the answers

After replication, DNA ligase is responsible for joining ______ fragments.

<p>Okazaki</p> Signup and view all the answers

DNA replication is not ______ accurate.

<p>100%</p> Signup and view all the answers

DNA Pol makes ______.

<p>mistakes</p> Signup and view all the answers

The mechanism used to correct DNA errors is called ______.

<p>MMR</p> Signup and view all the answers

Xeroderma pigmentosum is caused by mutations in the genes involved in ______.

<p>NER</p> Signup and view all the answers

Individuals with Werner's syndrome experience ______ aging.

<p>premature</p> Signup and view all the answers

A ______ mutation occurs when one base is incorrectly added during replication.

<p>substitution</p> Signup and view all the answers

Cystic fibrosis is linked to a ______ mutation.

<p>deletion</p> Signup and view all the answers

Inversions involve a region of a chromosome being ______ and reinserted.

<p>flipped</p> Signup and view all the answers

In DNA replication, the stage where the DNA double helix unwinds is called ______.

<p>unwinding</p> Signup and view all the answers

The process of synthesizing RNA primers is performed during the ______ stage.

<p>primer synthesis</p> Signup and view all the answers

In bacterial DNA replication, the ______ strand is synthesized in continuous fashion.

<p>leading</p> Signup and view all the answers

Nucleotide incorporation occurs where each nucleotide is a nucleotide ______.

<p>triphosphate</p> Signup and view all the answers

DNA polymerase III is essential for synthesizing DNA on both the ______ and lagging strands.

<p>leading</p> Signup and view all the answers

In the context of DNA replication, ______ fragments are created on the lagging strand.

<p>Okazaki</p> Signup and view all the answers

The enzyme responsible for joining DNA fragments after replication is called ______.

<p>DNA ligase</p> Signup and view all the answers

The origin of ______ is the specific location where DNA replication begins.

<p>replication</p> Signup and view all the answers

Xeroderma pigmentosum results from mutations in the genes involved in ______.

<p>NER</p> Signup and view all the answers

Individuals with Werner's syndrome experience premature ______.

<p>aging</p> Signup and view all the answers

______ mutation occurs when one or more extra nucleotides are inserted into replicating DNA.

<p>Insertion</p> Signup and view all the answers

A deletion mutation often results in a ______.

<p>frameshift</p> Signup and view all the answers

The global incidence of Werner's syndrome is approximately ______ in 100,000.

<p>1</p> Signup and view all the answers

Sickle-cell anemia is linked to a ______ mutation.

<p>substitution</p> Signup and view all the answers

A chromosomal ______ results in an increased dosage from a region of a chromosome being repeated.

<p>duplication</p> Signup and view all the answers

What is a common effect of Xeroderma pigmentosum?

<p>Hypersensitivity to sunlight</p> Signup and view all the answers

Which type of mutation is associated with sickle-cell anemia?

<p>Substitution</p> Signup and view all the answers

Which mutation involves losing a segment of a chromosome?

<p>Deletion</p> Signup and view all the answers

What characterizes Werner's syndrome?

<p>Normal aging until adulthood</p> Signup and view all the answers

What is the impact of insertion mutations in DNA?

<p>They cause frameshifts</p> Signup and view all the answers

The life expectancy of individuals with Xeroderma pigmentosum is typically between which ages?

<p>29-37 years</p> Signup and view all the answers

What type of mutation can result in Opitz-Kaveggia syndrome?

<p>Inversion</p> Signup and view all the answers

What is the primary role of RNA primase in DNA replication?

<p>To synthesize RNA primers for DNA synthesis</p> Signup and view all the answers

What happens to the phosphate groups during nucleotide incorporation into a growing DNA strand?

<p>Two phosphate groups are released</p> Signup and view all the answers

Which stage of DNA replication follows the unwinding of the double helix?

<p>Primer synthesis</p> Signup and view all the answers

In bacterial DNA replication, what is unique about the lagging strand compared to the leading strand?

<p>It is synthesized in short segments</p> Signup and view all the answers

What is the function of DNA ligase during DNA replication?

<p>To join Okazaki fragments together</p> Signup and view all the answers

Which enzyme is primarily responsible for the synthesis of new DNA strands during replication?

<p>DNA polymerase III</p> Signup and view all the answers

What is the origin of replication?

<p>The sequence where DNA replication begins</p> Signup and view all the answers

What is the function of single-strand binding proteins during DNA replication?

<p>To stabilize unwound single strands of DNA</p> Signup and view all the answers

What is the primary genetic condition associated with mutations that lead to hypersensitivity to UV light?

<p>Xeroderma pigmentosum</p> Signup and view all the answers

Which type of mutation is characterized by the replacement of one base during DNA replication?

<p>Substitution</p> Signup and view all the answers

Which disorder is associated with delayed growth and premature aging, and is often diagnosed around age 24?

<p>Werner's syndrome</p> Signup and view all the answers

Which mutation type results in a frameshift due to the removal of one or more nucleotides?

<p>Deletion</p> Signup and view all the answers

What is the common consequence of insertion mutations in the DNA sequence?

<p>Frameshift that alters protein encoding</p> Signup and view all the answers

Which genetic syndrome is directly linked to loss of a chromosomal segment?

<p>Cri du chat syndrome</p> Signup and view all the answers

Which chromosomal mutation results in a section being flipped and reinserted?

<p>Inversion</p> Signup and view all the answers

What is the general global incidence of Werner's syndrome?

<p>1 in 100,000</p> Signup and view all the answers

Which process predominantly occurs during the elongation stage of DNA replication?

<p>Nucleotide incorporation</p> Signup and view all the answers

Which of the following enzymes is primarily responsible for the removal of RNA primers during DNA replication?

<p>DNA polymerase I</p> Signup and view all the answers

What role does helicase play in DNA replication?

<p>Unwinds the DNA double helix</p> Signup and view all the answers

In bacterial DNA replication, what is the primary difference between the leading and lagging strands?

<p>The leading strand is synthesized continuously, while the lagging strand is synthesized in fragments.</p> Signup and view all the answers

What is the primary function of the single-strand binding protein during DNA replication?

<p>To stabilize unwound DNA strands and prevent them from re-annealing</p> Signup and view all the answers

During nucleotide incorporation, what happens to the phosphate groups of nucleotide triphosphates?

<p>Two phosphate groups are lost as the nucleotide is incorporated.</p> Signup and view all the answers

What is the function of DNA ligase in the context of DNA replication?

<p>To join together Okazaki fragments</p> Signup and view all the answers

Which of the following statements accurately describes the stages of DNA replication?

<p>Elongation follows unwinding and primer synthesis.</p> Signup and view all the answers

What is one consequence of Xeroderma pigmentosum?

<p>Hypersensitivity to sunlight</p> Signup and view all the answers

Which mutation type is identified as causing frameshifts by inserting extra nucleotides?

<p>Insertion mutation</p> Signup and view all the answers

What is a common feature of Werner's syndrome?

<p>Global incidence of 1:100,000</p> Signup and view all the answers

Which genetic disorder is linked to mutations in genes involved in nucleotide excision repair (NER)?

<p>Xeroderma pigmentosum</p> Signup and view all the answers

What type of mutation involves a segment of DNA being lost?

<p>Deletion mutation</p> Signup and view all the answers

What is the average life expectancy of individuals with Xeroderma pigmentosum?

<p>29-37 years</p> Signup and view all the answers

What disease is associated with a mutation that causes premature aging and is usually diagnosed around the age of 24?

<p>Werner's syndrome</p> Signup and view all the answers

Which condition is associated with a specific deletion mutation leading to significant health issues?

<p>Cri du chat syndrome</p> Signup and view all the answers

What are the four stages of DNA replication in the correct order?

<p>Initiation, Unwinding, Primer synthesis, Elongation</p> Signup and view all the answers

During DNA replication, which enzyme is responsible for adding nucleotides to the growing DNA strand?

<p>DNA polymerase III</p> Signup and view all the answers

What happens to the phosphate groups during nucleotide incorporation into DNA?

<p>Two phosphate groups are lost</p> Signup and view all the answers

What is the role of single-strand binding proteins in DNA replication?

<p>To prevent DNA strands from re-annealing</p> Signup and view all the answers

In DNA replication, the lagging strand is synthesized in what manner?

<p>In short fragments known as Okazaki fragments</p> Signup and view all the answers

What key concept was demonstrated by the Meselson and Stahl experiment?

<p>The semi-conservative nature of DNA replication</p> Signup and view all the answers

What type of nucleotide is incorporated during DNA synthesis?

<p>Nucleotide triphosphate</p> Signup and view all the answers

Which of the following accurately reflects the overall directionality of DNA replication?

<p>Replication occurs exclusively 5' to 3' direction</p> Signup and view all the answers

What role does DNA polymerase serve during DNA replication?

<p>It adds nucleotides and performs proofreading.</p> Signup and view all the answers

Which mechanism is specifically responsible for correcting errors in base pairing during DNA replication?

<p>Mismatch Repair (MMR)</p> Signup and view all the answers

What type of DNA damage is Base Excision Repair (BER) primarily designed to fix?

<p>Small, non-helix-distorting base lesions</p> Signup and view all the answers

Which DNA repair mechanism employs the complementary strand as a template to restore a sequence?

<p>Mismatch Repair (MMR)</p> Signup and view all the answers

DNA damage from which of the following agents is recognized by repair mechanisms?

<p>Both chemical and physical agents</p> Signup and view all the answers

What is the primary consequence of errors in DNA replication if not corrected?

<p>Accumulation of mutations</p> Signup and view all the answers

Which repair mechanism is most effective for fixing complex lesions in DNA?

<p>Nucleotide Excision Repair (NER)</p> Signup and view all the answers

What is the primary goal of DNA repair mechanisms within the cell cycle?

<p>To ensure genomic stability and prevent disease</p> Signup and view all the answers

Which enzyme is primarily involved in proofreading during DNA replication?

<p>DNA Polymerase</p> Signup and view all the answers

Which DNA repair mechanism corrects errors that escape proofreading during replication?

<p>Mismatch Repair (MMR)</p> Signup and view all the answers

Which repair process is activated for small, non-helix-distorting base lesions?

<p>Base Excision Repair (BER)</p> Signup and view all the answers

What kind of DNA damage can X-rays typically cause?

<p>Double-strand breaks</p> Signup and view all the answers

Which mechanism helps ensure the integrity of genetic material by repairing double-strand breaks?

<p>Homologous Recombination (HR)</p> Signup and view all the answers

What impact does a failure in DNA repair mechanisms typically have on the cell?

<p>Accumulation of mutations</p> Signup and view all the answers

What type of DNA damage is most likely caused by ultraviolet (UV) radiation?

<p>Thymine dimers</p> Signup and view all the answers

Which characteristic of DNA polymerase primarily contributes to its proofreading function?

<p>Exonuclease activity</p> Signup and view all the answers

What role does DNA polymerase play in ensuring accuracy during DNA replication?

<p>It detects and excises incorrectly paired nucleotides.</p> Signup and view all the answers

Which repair mechanism is specifically used for correcting base pairing errors that escape proofreading?

<p>Mismatch Repair (MMR)</p> Signup and view all the answers

What type of DNA damage is specifically repaired by Homologous Recombination (HR)?

<p>Double-strand breaks</p> Signup and view all the answers

What is the main consequence of errors during DNA replication if not corrected?

<p>Accumulation of mutations</p> Signup and view all the answers

Which type of DNA repair is suitable for small, non-helix-distorting base lesions?

<p>Base Excision Repair (BER)</p> Signup and view all the answers

What initiates the process of DNA repair mechanisms within the cell cycle?

<p>The detection of DNA damage</p> Signup and view all the answers

Which of the following is considered a damaging agent that can affect DNA structure?

<p>X-rays</p> Signup and view all the answers

How does the Mismatch Repair (MMR) mechanism function to maintain genetic integrity?

<p>By recognizing mispaired bases and correcting them</p> Signup and view all the answers

Study Notes

DNA Replication & Repair

  • DNA replication is a process that creates a new double-stranded DNA molecule. Replication begins with the separation of the two strands of double-stranded DNA.
  • Learning objectives include understanding DNA replication processes, the molecular details, and the importance of DNA repair and mutations.
  • DNA is reproduced by semiconservative replication.
  • The complementarity of DNA strands allows each strand to act as a template for the other during synthesis.
  • The Meselson-Stahl experiment demonstrated semiconservative replication, showing that each new DNA molecule consists of one original strand and one new strand.

Three Models of DNA Replication

  • Conservative: Original DNA molecule remains intact, and a completely new molecule is created.
  • Semiconservative: Each new molecule contains one original and one new strand.
  • Dispersive: DNA molecules are composed of fragments of both original and new DNA.

The Meselson-Stahl Experiment

  • The experiment used isotopes of nitrogen (15N and 14N) to label DNA.
  • Bacteria were cultured in a 15N medium, then transferred to a 14N medium, and DNA was extracted at different time points.
  • Centrifugation of DNA samples allowed the researchers to determine the density of DNA, which indicated the model of DNA replication.

Where Replication Occurs in the Cell Cycle

  • DNA replication occurs during the S phase of interphase.
  • Interphase includes G1, S, and G2 phases.
  • During S phase, each chromosome is duplicated by the cell.
  • G2 is when the cell checks the duplicated chromosomes for errors.

Origins of Replication

  • Replication begins at specific sites on the DNA called origins of replication.
  • In prokaryotes (bacteria), replication typically has one origin of replication.
  • In eukaryotes (e.g., human cells), there are multiple origins of replication.
    • This allows replication to proceed faster and is associated with a replication bubble and replication forks.
    • replication forks are where the DNA strands separate to allow replication.

Four Stages of Replication

  • 1. Initiation: Topoisomerase relieves strain ahead of the replication fork, and helicase unwinds the DNA double helix. Single-strand binding proteins prevent the strands from re-annealing.
  • 2. Unwinding: Helicase breaks hydrogen bonds, separating the DNA strands.
  • 3. Primer Synthesis: Primase synthesizes RNA primers to provide a 3' end for DNA polymerase.
  • 4. Elongation: DNA polymerase extends the RNA primers with DNA nucleotides.

Nucleotide Incorporation

  • Nucleotides are added to the 3' end of the growing strand.
  • Two phosphate groups are lost as they join, providing energy for the reaction.
  • DNA polymerase adds complementary nucleotides to the template strand.

Bacterial DNA Replication: Leading and Lagging Strands

  • In bacterial DNA, replication proceeds in both directions from a single origin.
  • The leading strand is synthesized continuously.
  • The lagging strand is synthesized discontinuously in short fragments.
  • Okazaki fragments are short fragments of DNA synthesized on the lagging strand.
  • DNA ligase joins the Okazaki fragments together.

DNA Repair Mechanisms

  • DNA replication is a complex process that is not perfectly accurate. During this essential cellular function, initial mistakes in nucleotide incorporation can occur naturally, leading to mutations if not corrected. These errors can arise from various factors, including the inherent limitations of the DNA polymerase enzyme that is responsible for synthesizing the new DNA strand.
  • DNA polymerase can make mistakes in adding the right nucleotides, so proofreading is needed. This proofreading process involves DNA polymerase participating in a secondary function where it can detect and excise incorrectly paired nucleotides. This action greatly enhances the fidelity of DNA replication, reducing the mutation rate effectively.
  • DNA repair mechanisms ensure accuracy, thus maintaining genomic stability. These mechanisms are critical for cellular health and prevent the accumulation of mutations that can lead to diseases, including cancer. Several sophisticated pathways actively monitor and repair damaged DNA throughout the cell cycle.
  • MMR (Mismatch Repair) corrects errors in base pairing during replication, which is crucial in maintaining genetic integrity. This mechanism recognizes mispaired bases that escape proofreading, removes the erroneous segment of DNA, and fills in the correct nucleotides using the complementary strand as a template, thus restoring the sequence.

DNA Damage and Repair

  • Various damaging agents (e.g., X-rays, UV, chemicals) can cause damage to DNA. These agents can lead to different forms of DNA damage, ranging from single-strand breaks to more complex lesions that may disrupt the DNA structure.
  • Several repair processes exist to fix the breaks and abnormalities in the DNA molecule. Depending on the type of damage, different pathways are employed, such as Base Excision Repair (BER) for small, non-helix-distorting base lesions, or Homologous Recombination (HR) that is utilized for repairing double-strand breaks, ensuring that the integrity of the genetic material is preserved.

Hereditary DNA Repair Disorders

  • Xeroderma pigmentosum: Characterized by hypersensitivity to UV light, increased skin cancer incidence, and premature aging, due to mutations in genes involved in nucleotide-excision repair (NER).
  • Werner's syndrome: A disorder involving premature aging and retarded growth, due to mutations in DNA repair genes.

Mutations

  • Mutations are changes in DNA sequence.
  • Different types of mutations exist (Point, Chromosome).
  • Mutations can be categorized based on the change's nature or consequences (e.g., substitution, frameshift).

Genetic Polymorphism

  • A genetic polymorphism represents the presence of two or more relatively common forms of a gene in a population.
  • Single nucleotide polymorphisms (SNPs) are common examples, where a single nucleotide differs between forms of a gene.

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DNA Replication & Repair Lecture 2 2024-2025 PDF

Description

Test your knowledge on DNA replication processes and repair mechanisms. This quiz covers key concepts such as the models of DNA replication, the significance of the Meselson-Stahl experiment, and the role of mutations in DNA. Dive into the molecular details and enhance your understanding of this fundamental topic.

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