DNA Damage and Replication Overview
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Questions and Answers

What is the immediate consequence when a DNA replication fork encounters a lesion in the DNA template, and it bypasses it?

  • Replication stalls until the lesion is repaired.
  • Translesion synthesis occurs with aid of a specific DNA polymerase.
  • A single-strand gap is formed, and replication continues downstream. (correct)
  • The replication fork collapses due to a double strand break.

    • Which of the following describes a scenario where a lesion in the template strand does not necessarily stall the replication fork?

  • When an O-meG base is present, which pairs with thymine. (correct)
  • When the lesion is a base that causes a significant DNA distortion.
  • When the lesion is undergoing nucleotide excision repair.
  • When a translesion DNA polymerase is used.

    • What is the most frequent immediate outcome when the replisome encounters a lesion in the DNA template before repair?

  • The replication fork collapses resulting in a double-strand break.
  • The replisome continues to synthesise over the lesion, using a specialised DNA polymerase.
  • The replication fork stalls, waiting for damage repair. (correct)
  • The replisome bypasses the lesion, leading to a downstream gap.

    • What directly leads to the collapse of the replication fork, creating a double strand break?

    <p>The replication fork encountering a lesion that is undergoing repair. (A)</p> Signup and view all the answers

    How does translesion synthesis (TLS) differ from normal DNA replication?

    <p>TLS utilizes specialized DNA polymerase that can synthesize over lesions. (A)</p> Signup and view all the answers

    What is the significance of an O-meG base in the template strand for DNA replication?

    <p>It can result in a C to T transition mutation due to mispairing with thymine. (B)</p> Signup and view all the answers

    Which process is required to restore an undamaged replication fork following a double-strand break resulting from a stalled replication fork?

    <p>Recombinational DNA repair. (A)</p> Signup and view all the answers

    Why is damage to DNA considered to be highly deleterious?

    <p>The consequences can cause mutations upon DNA replication. (C)</p> Signup and view all the answers

    What is the immediate consequence of a DNA lesion that blocks the replication machinery but allows it to resume further downstream?

    <p>A single-strand gap with no complementary strand at the location of the lesion (C)</p> Signup and view all the answers

    Why is a lesion in the lagging strand more easily bypassed by the replication machinery?

    <p>The mechanism for initiating Okazaki fragments allows for continuation downstream (B)</p> Signup and view all the answers

    What is the initial step in the recombinational repair of a double-strand break (DSB)?

    <p>Degradation of 5' ends to create 3' single-stranded overhangs (A)</p> Signup and view all the answers

    What is the role of the homologous DNA molecule in double-strand break (DSB) repair?

    <p>It serves as a template for restoring genetic information (C)</p> Signup and view all the answers

    What is the key characteristic of the strand invasion process during homologous recombination?

    <p>The displacement and base-pairing of a 3' single-stranded extension with a homologous strand (A)</p> Signup and view all the answers

    What is the significance of using the 3' ends for single strand invasion?

    <p>They can act directly as primers for DNA synthesis (C)</p> Signup and view all the answers

    What is a 'D-loop' in the context of recombinational DNA repair?

    <p>A temporary structure formed by strand invasion of a 3' single-stranded extension (A)</p> Signup and view all the answers

    What is the main difference between how DNA polymerase works in synthesis dependent strand annealing (SDSA), and general replication?

    <p>In SDSA, the invasion strand is used as a primer for synthesis, while generally, primers are RNA. (D)</p> Signup and view all the answers

    In synthesis-dependent strand annealing (SDSA), what happens to the lengthened invading strands after extension by the DNA polymerase?

    <p>They are displaced by helicases and anneal to each other (C)</p> Signup and view all the answers

    Which of the following enzymes is NOT directly involved in the early stages of recombinational DNA repair of a double strand break?

    <p>DNA Ligases (A)</p> Signup and view all the answers

    Study Notes

    DNA Damage and Replication

    • DNA damage is common and harmful. Consequences appear during replication.
    • Replication can continue over a lesion (translesion synthesis, TLS). Specialized polymerases aid TLS.
    • Normally, only specialized polymerases perform TLS. Regular polymerases might replicate some lesions without significant distortion.
    • A lesion can also stop replication, requiring repair before continuing or restart replication further downstream.
    • Replication can halt if a repair process is happening when a lesion is encountered. This can lead to a replication fork collapse and double-strand breaks.
    • Recombinational DNA repair restores the replication fork structure and allows replication to restart.
    • Most lesions cause the replication fork to stall. Replication ceases until repaired.
    • The replication machinery may bypass the lesion and resume downstream of the lesion.
    • This bypass plus restart phenomenon is frequent when the lesion is in the lagging strand.

    Double-Strand Breaks (DSBs)

    • DSBs occur due to oxidative DNA damage, oxygen-rich environments, or ionizing radiation.
    • DSBs are destructive and usually lethal if not repaired.
    • DSBs can arise from a broken template strand encountered by a replication fork during repair.
    • Recombination repairs DSBs. Repair requires a homologous, undamaged DNA molecule.
    • The repair DNA guides restoration of information lost at the break.
    • Repair initiation involves three enzymatic reactions:
      • Processing broken ends to create single-stranded extensions (overhangs)
      • Strand invasion of the homologous chromosome.
      • Replicative extension of the invading strand.

    Recombinational DNA Repair Process

    • Enzymes process broken DNA ends into 3' single-stranded extensions (overhangs).
    • Recombinase enzymes facilitate strand invasion of the homologous chromosome.
    • The invading strands are extended by DNA polymerases.
    • Several pathways resolve the "double crossover" intermediate, one of which is synthesis-dependent strand annealing (SDSA).

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    Description

    Explore the critical concepts surrounding DNA damage and its impact on replication. This quiz covers the mechanisms like translesion synthesis and the role of specialized polymerases in managing lesions. Understand the implications of replication fork stalling and the processes involved in DNA repair.

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