DNA Replication Enzymes Quiz
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Questions and Answers

What is the main function of topoisomerases during DNA replication?

  • Synthesize RNA primers for replication
  • Seal nicks in the DNA strand
  • Unwind double-stranded DNA (correct)
  • Add nucleotides to the growing DNA strand
  • Which DNA polymerase is primarily responsible for synthesizing the leading strand in eukaryotes?

  • DNA polymerase α
  • DNA polymerase γ
  • DNA polymerase β
  • DNA polymerase δ (correct)
  • Which DNA polymerase is exclusively used for the repair of DNA in eukaryotic cells?

  • DNA polymerase ε
  • DNA polymerase α
  • DNA polymerase δ
  • DNA polymerase β (correct)
  • What type of activity does DNA polymerase possess to correct mismatched nucleotides during DNA replication?

    <p>3' to 5' exonuclease activity</p> Signup and view all the answers

    During DNA replication, what distinguishes the synthesis of the leading strand from the lagging strand?

    <p>The leading strand is synthesized continuously while the lagging strand is not.</p> Signup and view all the answers

    What is the role of RNA primase in DNA replication?

    <p>To synthesize the RNA primer</p> Signup and view all the answers

    How do DNA helicases contribute to DNA replication?

    <p>By unwinding double-stranded DNA</p> Signup and view all the answers

    Which of the following is NOT a type of DNA polymerase found in prokaryotes?

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

    What is the direction of synthesis for the leading strand during DNA replication?

    <p>5' → 3' toward the replication fork</p> Signup and view all the answers

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

    <p>nucleases such as RNase H or polymerase I</p> Signup and view all the answers

    What are Okazaki fragments associated with in DNA replication?

    <p>Lagging strand synthesis</p> Signup and view all the answers

    In which direction do DNA polymerases read the template strand during replication?

    <p>3' → 5'</p> Signup and view all the answers

    Which polymerase is primarily responsible for synthesizing the leading strand in prokaryotes?

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

    What is the primary role of DNA ligase during DNA replication?

    <p>To catalyze the formation of phosphodiester bonds between Okazaki fragments</p> Signup and view all the answers

    Which statement accurately describes the function of RNA primers in DNA replication?

    <p>They provide a free 3' OH group for DNA polymerases to start synthesis.</p> Signup and view all the answers

    What is a key feature of the lagging strand during DNA replication?

    <p>It is synthesized in small, disjointed fragments.</p> Signup and view all the answers

    What is the primary function of topoisomerases during DNA replication?

    <p>To prevent supercoiling and relieve torsional strain</p> Signup and view all the answers

    Which statement describes the role of DNA helicases in DNA replication?

    <p>They unwind the double helix by breaking hydrogen bonds.</p> Signup and view all the answers

    What is the significance of the primer in DNA replication?

    <p>It acts as a template for DNA polymerization.</p> Signup and view all the answers

    What type of topoisomerase creates transient breaks in both strands of the DNA double helix?

    <p>Type II topoisomerases</p> Signup and view all the answers

    Which of the following statements about single-stranded DNA-binding (SSB) proteins is correct?

    <p>They protect ssDNA from degradation and help keep the strands separated.</p> Signup and view all the answers

    In the context of DNA replication, what distinguishes the leading strand from the lagging strand?

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

    What is the role of DNA polymerases during replication?

    <p>To synthesize the new DNA strand using the template of the existing strand.</p> Signup and view all the answers

    Which statement accurately reflects the action of Type I topoisomerases?

    <p>They create transient breaks in one strand of the double helix to relieve supercoiling.</p> Signup and view all the answers

    Study Notes

    DNA Replication Enzymes

    • DNA polymerases are the main enzymes involved in DNA replication, reading the template DNA in the 3' to 5' direction and synthesizing a new strand in the 5' to 3' direction. They have a proofreading activity, recognizing and removing mismatched nucleotides.
    • DNA polymerase I is primarily a repair enzyme for prokaryotes, with both 5' to 3' and 3' to 5' exonuclease activity.
    • DNA polymerase III is the primary enzyme for leading and lagging strand synthesis in prokaryotes.
    • In eukaryotes, DNA polymerase α is responsible for generating primers, DNA polymerase β is used for repair, DNA polymerase δ is the lead polymerase in DNA synthesis, and DNA polymerase γ functions in mitochondria.
    • DNA helicases are essential for unwinding double-stranded DNA.
    • DNA primase synthesizes short RNA primers, which are necessary for DNA polymerase to initiate synthesis.
    • Nick sealing enzymes are responsible for joining DNA fragments and closing gaps. These include topoisomerases and DNA ligase.
    • Single-stranded binding proteins (SSB proteins) bind to single-stranded DNA, preventing re-annealing and protecting the strands from degradation.

    DNA Replication Steps

    • Separation of the two strands: The two strands of parental DNA must separate for replication. This happens at a specific site called the origin of replication (Ori). In prokaryotes, there is one Ori, while in eukaryotes, there are multiple origins. The unwinding and separation create a "V" shape called the replication fork.
    • Formation of RNA primers: DNA primase synthesizes short RNA primers, approximately 10 nucleotides long, complementary to the DNA template strand. Primers are necessary for DNA polymerases to initiate synthesis.
    • Formation of two new strands: Both parent strands serve as templates for DNA synthesis, generating two new daughter strands. The DNA polymerases read the template strand in the 3' to 5' direction and synthesize the new strand in the 5' to 3' direction. This process is called semi-conservative replication.
      • Leading strand: Synthesized continuously in the 5' to 3' direction toward the replication fork.
      • Lagging strand: Synthesized discontinuously in the 5' to 3' direction away from the replication fork, forming short fragments called Okazaki fragments.
    • Excision of RNA primer and replacement by DNA: The RNA primers are removed by nucleases (like RNase H in eukaryotes or polymerase I in prokaryotes) and then replaced by DNA nucleotides using another DNA polymerase (polymerase I).
    • Joining Okazaki fragments: DNA ligase joins the Okazaki fragments, creating a continuous DNA strand.
    • Replication fork movement: Replication forks proceed in both directions away from the origin of replication, resulting in bidirectional replication.

    Proteins Required for DNA Strand Separation

    • DNA binding protein: Binds to specific DNA sequences at the origin of replication and initiates melting of AT rich regions leading to strand separation.
    • DNA helicases: Bind to single-stranded DNA near the replication fork and unwind the helix using ATP.
    • Single-stranded DNA-binding (SSB) proteins: Bind to single-stranded DNA, preventing re-annealing and protecting it from degradation. These proteins ensure the DNA is available for the polymerase to synthesize the new strand.
    • Topoisomerases: Relieve torsional stress and prevent the extreme supercoiling that would result from unwinding.
      • Type I topoisomerases: Cut one strand of the DNA helix, passing the other strand through the break, and then resealing the break.
      • Type II topoisomerases (DNA Gyrase): Cut both strands of the DNA helix, allowing the strands to unwind and then resealing the breaks.

    Origins of DNA Replication

    • In eukaryotes, DNA replication originates at multiple sites spaced every approximately 150 kilobases (kb) along the DNA molecule.

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    Related Documents

    Nucleic Acid Chemistry PDF

    Description

    Test your knowledge on the various enzymes involved in DNA replication, including those specific to prokaryotes and eukaryotes. This quiz covers functions, characteristics, and the significance of different DNA polymerases, helicases, and primase. Challenge yourself and see how well you understand this fundamental biological process!

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