Chapter 15
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Questions and Answers

What is the name of the enzyme that joins the Okazaki fragments?

  • DNA polymerase III
  • DNA ligase (correct)
  • DNA polymerase I
  • Primase

    • What is the problem with replicating the lagging strand at the end of a linear chromosome?

  • The replisome cannot coordinate the replication
  • The Okazaki fragments are not synthesized correctly
  • The leading strand cannot reach the end
  • DNA polymerase cannot add to the end without a primer (correct)

    • What is the term for the region at the end of a eukaryotic chromosome?

  • Chromatin
  • Telomere (correct)
  • Replisome
  • Centromere

    • How are the leading and lagging strands replicated in relation to each other?

    <p>The leading and lagging strands are replicated coordinately by a replisome</p> Signup and view all the answers

    What is the role of DNA polymerase I in lagging strand synthesis?

    <p>It removes the RNA primers and replaces them with DNA</p> Signup and view all the answers

    What is the purpose of the RNA primer in lagging strand synthesis?

    <p>To initiate Okazaki fragment synthesis</p> Signup and view all the answers

    What is the direction of DNA synthesis catalyzed by DNA polymerase?

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

    What provides the energy input for polymerizing DNA?

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

    How many replication bubbles are formed in bacterial cells during DNA replication?

    <p>One, at the origin of replication</p> Signup and view all the answers

    What is the direction of movement of the replication forks during DNA replication?

    <p>Away from the origin of replication</p> Signup and view all the answers

    How do eukaryotic cells differ from bacterial cells in terms of replication bubbles?

    <p>Eukaryotic cells have multiple replication bubbles, one on each chromosome</p> Signup and view all the answers

    What is the role of DNA polymerase in DNA synthesis?

    <p>To catalyze the synthesis of DNA</p> Signup and view all the answers

    What is the primary function of DNA helicase during DNA replication?

    <p>To separate the two strands of DNA</p> Signup and view all the answers

    What is the role of single-strand DNA-binding proteins (SSBPs) during DNA replication?

    <p>To attach to separated DNA strands and prevent them from closing</p> Signup and view all the answers

    What is the direction of synthesis for DNA polymerase?

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

    What is the limitation of DNA polymerase in terms of starting synthesis?

    <p>It can only extend from the 3' end of an existing strand</p> Signup and view all the answers

    What is the result of 5' → 3' synthesis on the two strands of DNA?

    <p>The opposite direction of synthesis on the two strands</p> Signup and view all the answers

    What is the purpose of Topoisomerase during DNA replication?

    <p>To relieve tension on the DNA molecule ahead of the fork</p> Signup and view all the answers

    What is the consequence of single-stranded DNA being left at the end of the lagging strand during replication?

    <p>It would shorten the chromosome by 50 to 100 nucleotides each time replication occurs.</p> Signup and view all the answers

    What is the primary function of telomerase?

    <p>To replicate telomeres, using an RNA template.</p> Signup and view all the answers

    What is the purpose of the single-stranded 'overhang' formed during telomere replication?

    <p>It provides a binding site for telomerase.</p> Signup and view all the answers

    What is the consequence of telomere shortening during replication?

    <p>Linear chromosomes would eventually vanish.</p> Signup and view all the answers

    Where is telomerase primarily found?

    <p>In gametes and stem cells.</p> Signup and view all the answers

    What is the end replication problem?

    <p>The shortening of chromosomes during replication.</p> Signup and view all the answers

    What is the role of primase in DNA synthesis?

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

    In which direction is the leading strand synthesized?

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

    What is the name of the process by which the lagging strand is synthesized?

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

    What is the function of DNA polymerase in leading strand synthesis?

    <p>To add dNTPs to the primer</p> Signup and view all the answers

    What is the problem faced during telomere replication?

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

    What is the replisome responsible for?

    <p>Coordinating leading and lagging strand synthesis</p> Signup and view all the answers

    Study Notes

    The End Replication Problem

    • Single-stranded DNA is left at the end of the lagging strand during replication
    • This single-stranded DNA is eventually degraded, which would shorten the chromosome by 50 to 100 nucleotides each time replication occurs
    • Over time, linear chromosomes would vanish if not for the solution of telomeres

    Telomeres and Telomerase

    • Telomeres are regions at the end of eukaryotic chromosomes that do not contain genes
    • Consist of short, repeating stretches of bases
    • Telomerase solves the end replication problem by replicating telomeres using an RNA template
    • Telomerase adds short DNA sequences to the end of the parent strand, preventing the shortening of telomeres

    Effect of Telomere Length on Cell Division

    • Telomerase is primarily found in gametes and stem cells, as well as in cancer cells
    • Telomere length affects cell division, with shorter telomeres limiting the number of cell divisions

    Lagging Strand Synthesis

    • The lagging strand is synthesized as short, discontinuous fragments called Okazaki fragments
    • DNA polymerase I removes the RNA primers and replaces them with DNA
    • The enzyme DNA ligase joins the Okazaki fragments, making the lagging strand intact

    DNA Replication

    • DNA replication occurs in a 5' → 3' direction
    • The leading strand is synthesized continuously in the 5' → 3' direction
    • The lagging strand is synthesized discontinuously in the 5' → 3' direction
    • Replication bubbles form at specific sequences, known as origins of replication, and grow in two directions
    • The replisome is a large grouping of enzymes that coordinates DNA replication

    Enzymes Involved in DNA Replication

    • Helicase: separates the two strands of DNA
    • Single-Strand Binding Proteins: holds separated single strands apart
    • Topoisomerase: relieves tension on the DNA molecule ahead of the fork
    • RNA primase: synthesizes a short piece of RNA (the primer)
    • DNA polymerase III: adds nucleotides to the primer
    • DNA polymerase I: a repair enzyme that removes the RNA primer
    • DNA ligase: repairs the sugar-phosphate backbone

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